chapter 11: dna and genes 11.pdfdna and genes 280 what you’ll learn you will relate ... objective...
TRANSCRIPT
DNA and GenesDNA and Genes
280
What Yoursquoll Learn You will relate the structure
of DNA to its function You will explain the role of
DNA in protein production You will distinguish among
different types of mutations
Why Itrsquos ImportantAn understanding of geneticdisorders viral diseases canceraging genetic engineering andeven criminal investigationsdepends upon knowing aboutDNA how it holds informationand how it plays a role in pro-tein production
Robert Harding World ImageryAlamy Images
Visit tobull study the entire chapter
onlinebull access Web Links for more
information and activities onDNA and genes
bull review content with theInteractive Tutor and self-check quizzes
Shetland ponies originated inShetlandmdasha group of islands off the coast of Scotland Theislands are mostly barren andhave extremely cold winters Dueto the isolation of these islandsin the past the characteristics ofthe ponymdashsmall stature thickhair (coat mane and tail)strength and hardinessmdasharefirmly imprinted in its DNA
Understandingthe Photo
ncbdolglencoecom
0280 C11CO BDOL-829900 8304 954 PM Page 280
111SECTION PREVIEWObjectivesAnalyze the structure ofDNADetermine how the struc-ture of DNA enables it toreproduce itself accurately
Review Vocabularynucleotide subunit of a
nucleic acid formed froma simple sugar a phos-phate group and anitrogenous base (p 163)
New Vocabularynitrogenous basedouble helixDNA replication
111 DNA THE MOLECULE OF HEREDITY 281
What is DNA Although the environment influences how an organism develops the
genetic information that is held in the molecules of DNA ultimatelydetermines an organismrsquos traits DNA achieves its control by determiningthe structure of proteins Living things contain proteins Your skin con-tains protein your muscles contain protein and your bones contain pro-tein mixed with minerals All actions such as eating running and eventhinking depend on proteins called enzymes Enzymes are critical for anorganismrsquos function because they control the chemical reactions neededfor life Within the structure of DNA is the information for lifemdashthecomplete instructions for manufacturing all the proteins for an organism
DNA as the genetic materialIn the early 1950s many scientists believed that protein was the genetic
material mainly because the structure of these large molecules was sovaried In 1952 however Alfred Hershey and Martha Chase performedexperiments using radioactively labeled viruses that infect bacteria
Lifersquos InstructionsUsing an Analogy Can youimagine all of the informationthat could be contained in 1000textbooks Remarkably thatmuch informationmdashandmoremdashis carried by the genesof a single organism Scientistshave found that the DNA con-tained in genes holds this infor-mation Because of the uniquestructure of DNA new copiesof the information can beeasily reproducedList Make a list of currentevents issues concerningDNA that you may have readabout in a newspaper As youread this section refer to yourlist and add explanations from the text
(t)Aaron Haupt (inset)CNRIPhototake NYC
Model of a DNA molecule
DNA The Molecule of Heredity
Objective 301 Analyze the molecular basis of heredityincluding DNA replication
North Carolina Objectives
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These viruses were made of only pro-tein and DNA Hershey and Chasecreated two different types of virusesOne type had radioactive DNA andthe other type had radioactive pro-tein Each type of virus infected aseparate bacteria culture Only theDNA entered the bacteria and pro-duced new viruses These results wereconvincing evidence that DNA is thegenetic material
The structure of nucleotidesDNA is capable of holding all its
information because it is a very longmolecule Recall that DNA is a polymermade of repeating subunits callednucleotides Nucleotides have threeparts a simple sugar a phosphategroup and a nitrogenous base Thesimple sugar in DNA called deoxyri-bose (dee ahk sih RI bos) gives DNA its namemdashdeoxyribonucleic acid Thephosphate group is composed of one
atom of phosphorus surrounded byfour oxygen atoms A nitrogenousbase is a carbon ring structure that con-tains one or more atoms of nitrogen InDNA there are four possible nitroge-nous bases adenine (A) guanine (G)cytosine (C) and thymine (T) Thus inDNA there are four possible nucleo-tides each containing one of these fourbases as shown in Figure 111
Nucleotides join together to formlong chains with the phosphate groupof one nucleotide bonding to thedeoxyribose sugar of an adjacentnucleotide The phosphate groups anddeoxyribose molecules form the back-bone of the chain and the nitrogenousbases stick out like the teeth of a zipperIn DNA the amount of adenine isalways equal to the amount of thymineand the amount of guanine is alwaysequal to the amount of cytosine Youcan see this in the Problem-Solving Labon the next page
282 DNA AND GENES
Purines Pyrimidines
Nucleotide
O
N
N
N
NN
Adenine (A)
O
Ondash
O = P ndash O
OH
H
H
H H
H
H
HSugar
(deoxyribose)
Nitrogenous basePhosphate group
CH2
H
N
N
N
N
N
Guanine (G)
O
N
N
N
N
N
N
Thymine (T)
H
CH3
Cytosine (C)
O
OH
H
N
N
N
H
H
O
AA BB
CCFigure 111Double-ringed nitrogenousbasesmdashadenine and guaninemdasharecalled purines (A) Single-ringednitrogenous basesmdashthymine andcytosinemdashare called pyrimidines(B) Each of the four nucleotidesthat make up DNA contains aphosphate group the sugardeoxyribose and one of four different nitrogenous bases (C)
0281-0287 C11S1 BDOL-829900 8304 1010 PM Page 282
283
The structure of DNAIn 1953 James Watson and Francis
Crick published a letter in a journalthat was only one page in length yetmonumental in importance Watsonand Crick proposed that DNA ismade of two chains of nucleotidesheld together by nitrogenous basesJust as the teeth of a zipper hold thetwo sides of the zipper together thenitrogenous bases of the nucleotideshold the two strands of DNA togetherwith weak hydrogen bonds Hydrogenbonds can form only between certainbases so the bases on one stranddetermine the bases on the otherstrand Specifically adenine on onestrand pairs only with thymine on theother strand and guanine on onestrand pairs only with cytosine on theother strand These paired basescalled complementary base pairsexplain why adenine and thymine arealways present in equal amountsLikewise the guanine-cytosine basepairs result in equal amounts of thesenucleotides in DNA Watson andCrick also proposed that DNA isshaped like a long zipper that is twistedinto a coil like a spring When some-thing is twisted like a spring the shapeis called a helix Because DNA is com-posed of two strands twisted togetherits shape is called a double helix Thisshape is shown in Figure 112
The importance of nucleotide sequences
A cattail a cat and a catfish are alldifferent organisms composed of differ-ent proteins If you compare the chro-mosomes of these organisms you willfind that they all contain DNA made upof the same four nucleotides with ade-nine thymine guanine and cytosine as their nitrogenous bases How canorganisms be so different from eachother if their genetic material is made of the same four nucleotides
Interpret the DataWhat does chemical analysis reveal about DNA Much ofthe early research on the structure and composition of DNAwas done by carrying out chemical analyses The data fromexperiments by Erwin Chargaff provided evidence of a rela-tionship among the nitrogenous bases of DNA
Solve the ProblemExamine the table below Compare the amounts of adenineguanine cytosine and thymine found in the DNA of each ofthe cells studied
Thinking Critically1 Compare and Contrast Compare the amounts of A T G
and C in each kind of DNA Why do you think the relativeamounts are so similar in human liver and thymus cells
2 Compare and Contrast How do the relative amounts ofeach base in herring sperm compare with the relativeamounts of each base in yeast
3 Summarize What fact can you state about the overallcomposition of DNA regardless of its source
Dan RichardsonThe Stock Shop
Figure 112DNA normally exists inthe shape of a doublehelix This shape is simi-lar to that of a twistedzipper
Percent of Each Base in DNA Samples
Source of Sample A G C T
Human liver 303 195 199 303
Human thymus 309 199 198 294
Herring sperm 278 222 226 275
Yeast 317 182 174 326
0281-0287 C11S1 BDOL-829900 8304 1012 PM Page 283
Their differences result from thesequence of the four different nucleo-tides along the DNA strands as shownin Figure 113
The sequence of nucleotides formsthe unique genetic information of anorganism For example a nucleotidesequence of A-T-T-G-A-C carriesdifferent information from a sequenceof T-C-C-A-A-A In a similar waytwo six-letter words made of the sameletters but arranged in different orderhave different meanings The closerthe relationship is between twoorganisms the more similar theirDNA nucleotide sequences will be
The DNA sequences of a chimpanzeeare similar to those of a gorilla butdifferent from those of a rosebushScientists use nucleotide sequences to determine evolutionary relation-ships among organisms to determinewhether two people are related andto identify bodies of crime victims
Replication of DNAA sperm cell and an egg cell of two
fruit flies both produced throughmeiosis unite to form a fertilized eggFrom one fertilized egg a fruit flywith millions of cells is produced bythe process of mitosis Each cell has acopy of the DNA that was in the orig-inal fertilized egg As you havelearned before a cell can divide bymitosis or meiosis it must first makea copy of its chromosomes The DNAin the chromosomes is copied in aprocess called DNA replicationWithout DNA replication new cellswould have only half the DNA of theirparents Species could not survive and
C11-02C-828242
Sugar-phosphate backbone
Hydrogen bonds betweennitrogenous bases
Chromosome
A
A
A
P
P
P
P
D
D
D
D
D
D
D
D
P
T
T
T
G
G
C
C
284 DNA AND GENES
Figure 113The structure ofDNA is shownhere
In each chain of nucleotidesthe sugar of one nucleotideis joined to the phosphategroup of the next nucleotideby a covalent bond
A
Complementary base pairing produces a long two-stranded molecule that is often compared to a zipper As you can see the sides of the zipper areformed by the sugar and phosphate units while the teeth of the zipper are the pairs of bases
C
The two chains of nucleotidesin a DNA molecule are heldtogether by hydrogen bondsbetween the bases In DNAcytosine forms three hydrogen
bonds with guanine andthymine forms two
hydrogen bondswith adenine
B
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individuals could not grow or repro-duce successfully All organisms un-dergo DNA replication Figure 114Bshows bacterial DNA replicating
How DNA replicatesYou have learned that a DNA mole-
cule is composed of two strands eachcontaining a sequence of nucleotidesAs you know an adenine on one strandpairs with a thymine on the otherstrand Similarly guanine pairs withcytosine Therefore if you know theorder of bases on one strand you canpredict the sequence of bases on theother complementary strand In factpart of the process of DNA replicationis done in just the same way Duringreplication each strand serves as a pat-tern or template to make a new DNAmolecule How can a molecule serve asa template Examine Figure 115 onthe next page to find out
Replication begins as an enzymebreaks the hydrogen bonds betweenbases that hold the two strands
together thus unzipping the DNAAs the DNA continues to unzipnucleotides that are floating free inthe surrounding medium are attachedto their base pair by hydrogen bond-ing Another enzyme bonds thesenucleotides into a chain
This process continues until theentire molecule has been unzippedand replicated Each new strandformed is a complement of one of theoriginal or parent strands Theresult is the formation of two DNAmolecules each of which is identicalto the original DNA molecule
When all the DNA in all the chro-mosomes of the cell has been copiedby replication there are two copies ofthe organismrsquos genetic informationIn this way the genetic makeup of anorganism can be passed on to newcells during mitosis or to new genera-tions through meiosis followed bysexual reproduction
Explain why DNAmust unzip before it can be copied
111 DNA THE MOLECULE OF HEREDITY 285Dr Gopal MurtiScience Photo LibraryPhoto Researchers
Replication
DNA
Replication
Figure 114DNA replication produces two mol-ecules from one Compare Howdo the new molecules comparewith the original
When a DNAmolecule replicatestwo molecules areformed Eachmolecule has oneoriginal strand andone new strandNewly synthesizedstrands are shownin red
A
This DNA is replicating Replication is takingplace at the points where the DNA hasunzipped to create a ldquobubblerdquo
B
Color-enhanced TEM Magnification 75 000
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286 DNA AND GENES
Separation of strands When acell begins to copy its DNA the twonucleotide strands of a DNA moleculeseparate when the hydrogen bondsconnecting the base pairs are brokenAs the DNA molecule unzips thebases are exposed
AA
Base pairing The bases infree nucleotides pair withexposed bases in the DNAstrand If one nucleotide on astrand has thymine as a basethe free nucleotide that pairswith it would be adenine Ifthe strand contains cytosinea free guanine nucleotide willpair with it Thus each strandbuilds its complement by basepairingmdashforming hydrogenbondsmdashwith free nucleotides
BB
Bonding of bases The sugar andphosphate parts of adjacent nucleotidesbond together with covalent bonds toform the backbone of the new strandEach original strand is now hydrogen-bonded to a new strand
CC
Copying DNAFigure 115DNA is copied during interphase prior to mitosis andmeiosis It is important that the new copies are exactlylike the original molecules The structure of DNA providesa mechanism for accurate copying of the molecule Theprocess of making copies of DNA is called DNA replica-tion Critical Thinking What might be the outcome ifmitosis occurred before replication took place
D
P
D
P
D
P
P
D
D
P
D
P
D
P
Original DNA strand
New DNA strand
Original DNA
A
A
A
AA
T
T
T
T
G
G
G
G
C
C
C
C
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111 DNA THE MOLECULE OF HEREDITY 287Dr Gopal MurtiScience Photo LibraryPhoto Researchers
Understanding Main Ideas1 Describe the structure of a nucleotide
2 How do the nucleotides in DNA bond with eachother within a strand How do they bond witheach other across strands
3 Explain why the structure of a DNA molecule isoften described as a zipper
4 How does DNA hold information
Thinking Critically5 The sequence of nitrogenous bases on one strand
of a DNA molecule is GGCAGTTCATGC Whatwould be the sequence of bases on the comple-mentary strand
6 Get the Big Picture Sequence the steps thatoccur during DNA replication For more help referto Get the Big Picture in the Skill Handbook
SKILL REVIEWSKILL REVIEW
Results of replication The process ofreplication produces two molecules of DNA Eachnew molecule has one strand from the originalmolecule and one strand that has been newlysynthesized from free nucleotides in the cell
DD
Free nucleotides
New DNA molecule
New DNA molecule
TOriginal DNA strand
Two molecules of DNA from one
Color-enhanced TEM Magnification 75 000
ncbdolglencoecomself_check_quiz
0281-0287 C11S1 BDOL-829900 8304 1016 PM Page 287
From DNA to Protein112
Genes and ProteinsThe sequence of nucleotides in DNA contain information This infor-
mation is put to work through the production of proteins Proteins foldinto complex three-dimensional shapes to become key structures andregulators of cell functions Some proteins become important structuressuch as the filaments in muscle tissue Other proteins such as enzymescontrol chemical reactions that perform key life functionsmdashbreakingdown glucose molecules in cellular respiration digesting food or makingspindle fibers during mitosis In fact enzymes control all the chemicalreactions of an organism Thus by encoding the instructions for makingproteins DNA controls cells
You learned earlier that proteins are polymers of amino acids Thesequence of nucleotides in each gene contains information for assemblingthe string of amino acids that make up a single protein
Explain how DNA controls the activities of cells
RNARNA like DNA is a nucleic acid However RNA structure differs from
DNA structure in three ways shown in Figure 116 First RNA is singlestrandedmdashit looks like one-half of a zippermdashwhereas DNA is doublestranded The sugar in RNA is ribose DNArsquos sugar is deoxyribose
Sequence After you read Section 112 begin at the top tab and sequence the five steps of translation
Protein Synthesis Make the following Foldable to help you understand the process of protein formation
Collect 3 sheets of paper and layer them about 15 cm apart vertically Keep the edges level
Fold up the bottom edges of the paper to form 6 equal tabs
Fold the papers and crease well to hold the tabs in place Staple along the fold Label each tab
STEP 1
STEP 3
STEP 2
288 DNA AND GENES
SECTION PREVIEWObjectivesRelate the concept of thegene to the sequence ofnucleotides in DNASequence the stepsinvolved in protein synthesis
Review Vocabularypolymer a large molecule
formed from smaller sub-units that are bondedtogether (p 158)
New Vocabularymessenger RNAribosomal RNAtransfer RNAtranscriptioncodontranslation
Objective 301 Analyze the molecular basis of heredityincluding Protein synthesis (transcription translation) Gene regulation
North Carolina Objectives
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Finally both DNA and RNA containfour nitrogenous bases but ratherthan thymine RNA contains a simi-lar base called uracil (U) Uracilforms a base pair with adenine inRNA just as thymine does in DNA
What is the role of RNA in a cellPerhaps you have seen a car beingbuilt on an automobile assembly lineComplex automobiles are built inmany simple steps Engineers tellworkers how to make the cars andworkers follow directions to buildthe cars on the assembly lineSuppliers bring parts to the assemblyline so they can be installed in the car Protein production is similarto car production DNA providesworkers with the instructions formaking the proteins and workers
build the proteins Other workersbring parts the amino acids over tothe assembly line The workers forprotein synthesis are RNA mole-cules They take from DNA theinstructions on how the proteinshould be assembled thenmdashaminoacid by amino acidmdashthey assemblethe protein
There are three types of RNA thathelp build proteins Extending thecar-making analogy you can considerall three of these RNA molecules to be workers in the protein assemblyline One type of RNA messengerRNA (mRNA) brings instructionsfrom DNA in the nucleus to the cellrsquos factory floor the cytoplasm On the factory floor mRNA moves to the assembly line a ribosome
112 FROM DNA TO PROTEIN 289
CH
C
C CH
C
C
N
N
O
C
Hydrogenbonds Adenine
Uracil
Ribose
A
OH OH
H
O
H
O
O
O
O P O CH2
Phosphate
NH
N
N
N
N
H
H
C
C C
C
C H
P
R
C
P
RU
RG
C
H
Figure 116The three chemical differ-ences between DNA and RNAare shown here InterpretScientific Illustrations Whatis the three-dimensionalshape of RNA
The nitrogenous base uracil (U) replaces thymine (T)in RNA In RNA uracil forms base pairs with adeninejust as thymine does in DNA
C
Ribose is the sugarin RNA rather thanthe deoxyribosesugar in DNA
B
An RNA molecule usually consists of asingle strand of nucleotides not a doublestrand This single-stranded structure isclosely related to its function
A
0288-0295 C11S2 BDOL-829900 8304 1031 PM Page 289
The ribosome made of ribosomalRNA (rRNA) binds to the mRNAand uses the instructions to assemblethe amino acids in the correct orderThe third type of RNA transferRNA (tRNA) is the supplier TransferRNA delivers amino acids to the ribo-some to be assembled into a protein
TranscriptionHow does the information in DNA
which is found in the nucleus move tothe ribosomes in the cytoplasmMessenger RNA carries this informa-tion through the nuclear envelope tothe ribosomes for manufacturing pro-teins just as a worker carries informa-tion from the engineers to the assemblyline for manufacturing a car In thenucleus enzymes make an RNA copyof a portion of a DNA strand in a process called transcription(trans KRIHP shun) Follow the steps in Figure 117 as you read about transcription
The main difference between tran-scription and DNA replication is thattranscription results in the formationof one single-stranded RNA moleculerather than a double-stranded DNAmolecule
DNAstrand
DNAstrand
RNAstrand
RNAstrand
A
A
A
T
T
U U
G
G G
G
G
C
C
C
C
Figure 117Messenger RNA ismade during theprocess of transcription
290 DNA AND GENES
The process oftranscriptionbegins as enzymesunzip the moleculeof DNA in theregion of the geneto be transcribed
A
Free RNAnucleotides formbase pairs with theircomplementarynucleotides on theDNA strand ThemRNA strand iscomplete when theRNA nucleotides bondtogether
B
The mRNA strandbreaks away andthe DNA strandsrejoin The mRNAstrand leaves thenucleus and entersthe cytoplasm
C
0288-0295 C11S2 BDOL-829900 8304 1033 PM Page 290
112 FROM DNA TO PROTEIN 291
Modeling transcription in theBioLab on pages 302ndash303 will help youto understand this process You canfind out how scientists use new micro-scopes to ldquowatchrdquo transcription takeplace by reading the Biotechnology atthe end of the chapter
RNA ProcessingNot all the nucleotides in the DNA
of eukaryotic cells carry instructionsmdashor codemdashfor making proteins Genesusually contain many long noncodingnucleotide sequences called introns(for intervening regions) that are scat-tered among the coding sequencesRegions that contain information arecalled exons because they areexpressed When mRNA is transcribedfrom DNA both introns and exons arecopied The introns must be removedfrom the mRNA before it can functionto make a protein Enzymes in thenucleus cut out the intron segmentsand paste the mRNA back togetherThe mRNA then leaves the nucleusand travels to the ribosome
The Genetic CodeThe nucleotide sequence tran-
scribed from DNA to a strand of mes-senger RNA acts as a genetic messagethe complete information for thebuilding of a protein Think of thismessage as being written in a languagethat uses nitrogenous bases as itsalphabet As you know proteins con-tain chains of amino acids You couldsay that the language of proteins usesan alphabet of amino acids A code isneeded to convert the language ofmRNA into the language of proteinsThere are 20 common amino acidsbut mRNA contains only four types ofbases How can four bases form a codefor all possible proteins The Problem-Solving Lab shows you how
Formulate ModelsHow many nitrogenous bases determine an amino acidAfter the structure of DNA had been discovered scientists triedto predict the number of nucleotides that code for a singleamino acid It was already known that there were 20 aminoacids so at least 20 groups were needed If one nucleotide codedfor an amino acid then only four amino acids could be repre-sented How many nucleotides are needed
Solve the ProblemExamine the three safesLetters representingnitrogenous bases havereplaced numbers on thedials Copy the data tableCalculate the possiblenumber of combinationsthat will open the safe ineach diagram using the formula provided in the table The 4corresponds to the number of letters on each dial the super-script refers to the number of available dials
Thinking Critically 1 Use Models Using Safe 1 write down several examples of
dial settings that might open the safe Do the total possi-ble combinations seen in Safe 1 equal or surpass the totalnumber of common amino acids
2 Analyze Could a nitrogenous base (A T C or G) takenone at a time code for 20 different amino acids Explain
3 Use Numbers Using Safe 2 write down several examplesof dial combinations that might open the safe Do thetotal possible combinations seen in Safe 2 equal or surpassthe total number of common amino acids
4 Analyze Could nitrogenous bases taken two at a timecode for 20 different amino acids Explain
5 Analyze Could nitrogenous bases taken three at a timecode for 20 different amino acids Explain
6 Draw Conclusions Does the analogy prove that threebases code for an amino acid Explain
T
G
C
A
T
G
C
A
T
G
C
A T
G
C
A
T
G
C
A
T
G
C
A
Safe 1 Safe 2 Safe 3
Data Table
Number TotalNumber of Letters Possible Formulaof Dials per Dial Combinations
Safe 1 41
Safe 2 42
Safe 3 43
0288-0295 C11S2 BDOL-829900 8304 1035 PM Page 291
Biochemists began to crack thegenetic code when they discoveredthat a group of three nitrogenousbases in mRNA code for one aminoacid Each group is known as a codonFor example the codon UUU resultsin the amino acid phenylalanine beingplaced in a protein
Sixty-four combinations are possi-ble when a sequence of three bases isused thus 64 different mRNAcodons are in the genetic codeshown in Table 111 Some codonsdo not code for amino acids theyprovide instructions for making theprotein For example UAA is a stopcodon indicating that the proteinchain ends at that point AUG is astart codon as well as the codon forthe amino acid methionine As youcan see more than one codon cancode for the same amino acidHowever for any one codon therecan be only one amino acid
All organisms use the same geneticcode For this reason it is said to beuniversal and this provides evidencethat all life on Earth evolved from acommon origin From the chloro-phyll of a birch tree to the digestiveenzymes of a bison a large number ofproteins are produced from DNA It may be hard to imagine that onlyfour nucleotides can produce so many diverse proteins yet thinkabout computer programming Youmay have seen computer code such as 00010101110000110 Through a binary language with only twooptionsmdashzeros and onesmdashmanytypes of software are created Fromcomputer games to World WideWeb browsers complex software isbuilt by stringing together the zerosand ones of computer code into longchains Likewise complex proteinsare built from the long chains ofDNA carrying the genetic code
292 DNA AND GENES
Table 111 The Messenger RNA Genetic Code
First ThirdLetter Second Letter Letter
U C A G
U Phenylalanine (UUU) Serine (UCU) Tyrosine (UAU) Cysteine (UGU) U
Phenylalanine (UUC) Serine (UCC) Tyrosine (UAC) Cysteine (UGC) C
Leucine (UUA) Serine (UCA) Stop (UAA) Stop (UGA) A
Leucine (UUG) Serine (UCG Stop (UAG) Tryptophan (UGG) G
C Leucine (CUU) Proline (CCU) Histidine (CAU) Arginine (CGU) U
Leucine (CUC) Proline (CCC) Histidine (CAC) Arginine (CGC) C
Leucine (CUA) Proline (CCA) Glutamine (CAA) Arginine (CGA) A
Leucine (CUG) Proline (CCG) Glutamine (CAG) Arginine (CGG) G
A Isoleucine (AUU) Threonine (ACU) Asparagine (AAU) Serine (AGU) U
Isoleucine (AUC) Threonine (ACC) Asparagine (AAC) Serine (AGC) C
Isoleucine (AUA) Threonine (ACA) Lysine (AAA) Arginine (AGA) AMethionine Threonine (ACG) Lysine (AAG) Arginine (AGG) GStart (AUG)
G Valine (GUU) Alanine (GCU) Aspartate (GAU) Glycine (GGU) U
Valine (GUC) Alanine (GCC) Aspartate (GAC) Glycine (GGC) C
Valine (GUA) Alanine (GCA) Glutamate (GAA) Glycine (GGA) A
Valine (GUG) Alanine (GCG) Glutamate (GAG) Glycine (GGG) G
0288-0295 C11S2 BDOL-829900 8504 951 AM Page 292
Translation FrommRNA to Protein
How is the language of the nucleicacid mRNA translated into the lan-guage of proteins The process of con-verting the information in a sequenceof nitrogenous bases in mRNA into asequence of amino acids in protein isknown as translation You can sum-marize transcription and translation bycompleting the MiniLab
Translation takes place at the ribo-somes in the cytoplasm In prokary-otic cells which have no nucleus themRNA is made in the cytoplasm In eukaryotic cells mRNA is madein the nucleus and travels to thecytoplasm In the cytoplasm a ribo-some attaches to the strand ofmRNA like a clothespin clampedonto a clothesline
The role of transfer RNAFor proteins to be built the 20 dif-
ferent amino acids dissolved in thecytoplasm must be brought to the ribo-somes This is the role of transfer RNA(tRNA) modeled in Figure 118 EachtRNA molecule attaches to only onetype of amino acid
PredictTranscribe and Translate Molecules of DNA carry thegenetic instructions for protein formation Converting theseDNA instructions into proteins requires a series of coordinatedsteps in transcription and translation
Procedure Copy the data table Complete column B by writing the correct mRNA codon
for each sequence of DNA bases listed in the columnmarked DNA Base Sequence Use the letters A U C or G
Identify the process responsible by writing its name on thearrow in column A
$ Complete column D by writing the correct anticodon thatbinds to each codon from column B
Identify the process responsible by writing its name on thearrow in column C
^ Complete column E by writing the name of the correctamino acid that is coded by each base sequence UseTable 111 on page 292 to translate the mRNA basesequences to amino acids
Analysis1 Recognize Spatial Relationships Where within the cell
a are the DNA instructions locatedb does transcription occurc does translation occur
2 Formulate Models Describe the structure of a tRNA molecule
3 Use Scientific Explanations Explain why specific basepairing is essential to the processes of transcription andtranslation
293
T
Anticodon
Aminoacid
Chain of RNAnucleotides
ransfer RNAmolecule
AA
U A C
Figure 118A tRNA molecule is composed of about 80 nucleotides Each tRNA rec-ognizes only one amino acid The amino acid becomes bonded to oneside of the tRNA molecule Located on the other side of the tRNA mol-ecule are three nitrogenous bases called an anticodon that pair upwith an mRNA codon during translation
Data Table
A B C D EDNA Base mRNA tRNA AminoSequence Process Codon Process Anticodon Acid
AAT rarr rarrGGG rarr rarrATA rarr rarrAAA rarr rarrGTT rarr rarr
0288-0295 C11S2 BDOL-829900 8304 1036 PM Page 293
Figure 119A protein is formed by the process of translation
AUGA U G AAG U GCUC C A A
mRNA codon
Ribosome
Methionine
AUGA
A
U
U
G AAG U GCUC
C
C A A
tRNA anticodon
AUGA U G AAG
G
U
U
GCUC
C
C A A
Alanine
U AC
Peptide bond
AUGA U G AAG U GCUC C A A
U AC G UC
Alanine
Peptidebond
Methionine
AAA U G AAG UC
A A C
C A
Stopcodon
A U GU U
294 DNA AND GENES
As translation begins a ribosome attaches to themRNA strand Molecules of tRNA each carrying aspecific amino acid approach the ribosome
AA
The codon AUG which codes for the amino acidmethionine signals the start of protein synthesis The tRNA molecule carrying methionine attaches to the ribosome and mRNA strand
BB A new tRNA molecule carrying an amino acidattaches to the ribosome and mRNA strand next to the previous tRNA molecule The amino acids on the tRNA molecules join by peptide bonds
CC
After the peptide bond is formed the ribosomeslides along the mRNA to the next codon The tRNAmolecule no longer carrying an amino acid isreleased A new tRNA molecule carrying an aminoacid can attach to the ribosome and mRNA strand
DD A chain of amino acids is formed until a stop codon is reached on the mRNA strand
EE
0288-0295 C11S2 BDOL-829900 8304 1036 PM Page 294
Correct translation of the mRNAmessage depends upon the joining ofeach mRNA codon with the correcttRNA molecule How does a tRNAmolecule carrying its amino acid rec-ognize which codon to attach to Theanswer involves base pairing There isa sequence of three nucleotides on theopposite side of the transfer-RNAmolecule from the amino-acid attach-ment site that is the complement ofthe nucleotides in the codon Thesethree nucleotides are called an anti-codon because they bind to the codonof the mRNA The tRNA carriesonly the amino acid that the anti-codon specifies For example onetRNA molecule for the amino acidcysteine has an anticodon of ACAThis anticodon binds to the mRNAcodon UGU
Translating the mRNA codeFollow the steps in Figure 119 as
you read how translation occurs Astranslation begins a tRNA moleculebrings the first amino acid to themRNA strand that is attached to theribosome Figure 119A The anti-codon forms a base pair with the codonof the mRNA strand Figure 119BThis places the amino acid in the cor-rect position for forming a peptidebond with the next amino acid Theribosome slides down the mRNA chain
to the next codon and a new tRNAmolecule brings another amino acidFigure 119C The amino acids bond the first tRNA releases its aminoacid and detaches from the mRNAFigure 119D The tRNA molecule isnow free to pick up and deliver anothermolecule of its specific amino acid to aribosome Again the ribosome slidesdown to the next codon a new tRNAmolecule arrives and its amino acidbonds to the previous one A chain ofamino acids begins to form When astop codon is reached translation endsand the amino acid strand is releasedfrom the ribosome Figure 119E
Amino acid chains become proteinswhen they are freed from the ribo-some and twist and curl into complexthree-dimensional shapes Each pro-tein chain forms the same shape everytime it is produced These proteinsbecome enzymes and cell structures
Now that you have followed theprocess of protein synthesis you haveseen that the pathway of informationflows from DNA to mRNA to pro-tein This scheme is called the centraldogma of biology and is found in allorganisms from the simplest bac-terium to the most complex plant andanimal The formation of proteinoriginating from the DNA code produces the diverse and magnificent living world
Understanding Main Ideas1 How does the DNA nucleotide sequence deter-
mine the amino acid sequence in a protein2 What is a codon and what does it represent3 What is the role of tRNA in protein synthesis4 Compare DNA replication and transcription
Thinking Critically5 You have learned that there are stop codons that
signal the end of an amino acid chain Why is it
important that a signal to stop translation be partof protein synthesis
6 Get the Big Picture Sequence the steps involvedin protein synthesis from the production of mRNAto the final translation of the DNA code For morehelp refer to Get the Big Picture in the SkillHandbook
SKILL REVIEWSKILL REVIEW
112 FROM DNA TO PROTEIN 295
codon from theLatin word codexmeaning ldquoa tabletfor writingrdquo Acodon is the three-nucleotide sequencethat codes for anamino acid
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0288-0295 C11S2 BDOL-829900 8304 1037 PM Page 295
113SECTION PREVIEWObjectivesCategorize the differentkinds of mutations thatcan occur in DNACompare the effects of different kinds of mutations on cells andorganisms
Review Vocabularycancer diseases believed to
be caused by changes inthe genes that controlthe cell cycle (p 211)
New Vocabularymutationpoint mutationframeshift mutationchromosomal mutationmutagen
296 DNA AND GENES
When Things Go WrongUsing Prior Knowledge Youknow that DNA controls thestructures and functions of a cellWhat happens when the sequenceof DNA nucleotides in a gene ischanged Sometimes it may havelittle or no harmful effectmdashlikethe thick tightly crimped fur onthis American Wirehair catmdashandthe DNA changes are passed onto offspring of the organism Atother times however the change can cause the cell to behave differ-ently For example in skin cancer UV rays from the sun damage theDNA and cause the cells to grow and divide rapidly Recognize Cause and Effect Why might a mutation have little or no harmfuleffect on an organism
MutationsIf the DNA in all the cells of an adult human body were lined up end
to end it would stretch nearly 100 billion kilometersmdash60 times the dis-tance from Earth to Jupiter This DNA is the end result of thousands ofreplications beginning with the DNA in a fertilized egg Organisms haveevolved many ways to protect their DNA from changes In spite of thesemechanisms however changes in the DNA occasionally do occur Anychange in the DNA sequence is called a mutation Mutations can becaused by errors in replication transcription cell division or by externalagents One such cause is discussed in Figure 1110
Mutations in reproductive cellsMutations can affect the reproductive cells of an organism by changing
the sequence of nucleotides within a gene in a sperm or an egg cell If thiscell takes part in fertilization the altered gene would become part of thegenetic makeup of the offspring The mutation may produce a new traitor it may result in a protein that does not work correctly resulting instructural or functional problems in cells and in the organismSometimes the mutation results in a protein that is nonfunctional andthe embryo may not survive
In some rare cases a gene mutation may have positive effects An organ-ism may receive a mutation that makes it faster or stronger such a mutationmay help an organismmdashand its offspringmdashbetter survive in its environment
Genetic Changes
Richard Katris
American Wirehair cat
PhysicalScience
Connection
PhysicalScience
Connection
Gamma radiationas a waveGamma radiationor gamma rays areelectromagneticwaves Gammaradiation is emittedby processes thatoccur in the nucleiof atoms Theyhave the shortestwavelengths andhighest frequenciesof any waves in theelectromagneticspectrum
0296-0307 C11S3 BDOL-829900 8304 1121 PM Page 296
BDOL-113
null
51485583
You will learn later that mutations thatbenefit a species play an important rolein the evolution of that species
Mutations in body cellsWhat happens if powerful radiation
such as gamma radiation hits the DNAof a nonreproductive cell a cell of thebody such as in skin muscle or bone Ifthe cellrsquos DNA is changed this muta-tion would not be passed on to off-spring However the mutation maycause problems for the individualDamage to a gene may impair the func-tion of the cell for example it maycause a cell in the stomach to lose itsability to make acid needed for diges-tion or a skin cell may lose its elasticityWhen that cell divides the new cellsalso will have the same mutation Manyscientists suggest that the buildup ofcells with less than optimal functioningis an important cause of aging
Some mutations of DNA in bodycells affect genes that control cell divi-sion This can result in the cells grow-ing and dividing rapidly producingcancer As you learned earlier canceris the uncontrolled dividing of cells
(tl)SIUVisuals Unlimited (tr)Visuals Unlimited (b)Grace MooreThe Stock ShopMedichrome
Genetic Counselor
A re you fascinated by how youinherit traits from your par-
ents If so you could become agenetic counselor and help peopleassess their risk of inheriting orpassing on genetic disorders
Skills for the JobGenetic counselors are medical pro-
fessionals who work on a health careteam They analyze familiesrsquo medical histories to determinethe parentsrsquo risk of having children with genetic disorderssuch as hemophilia or cystic fibrosis Counselors also edu-cate the public and help families with genetic disorders findsupport and treatment These counselors may work in amedical center a private practice research or a commerciallaboratory To become a counselor you must earn a two-year masterrsquos degree in medical genetics and pass a test tobecome certified The most important requirement is theability to listen and to help families make difficult decisions
For more careers in related fields visit
113 GENETIC CHANGES 297
AA BB
Figure 1110Nuclear power plant workers wear radiationbadges (A) and pocket dosimeters (B) to mon-itor their exposure to radiation Radiation cancause changes to DNA
ncbdolglencoecomcareers
0296-0307 C11S3 BDOL-829900 8304 1123 PM Page 297
Cancer results from gene mutationsFor example ultraviolet radiation insunlight can change the DNA in skincells The cells reproduce rapidlycausing skin cancer
Explain how muta-tions in body cells cause damage
The effects of point mutationsConsider what might happen if an
incorrect amino acid were insertedinto a growing protein chain duringthe process of translation The mis-take might affect the structure of theentire molecule Such a problem canoccur if a point mutation arises Apoint mutation is a change in a sin-gle base pair in DNA
A simple analogy can illustratepoint mutations Read the followingtwo sentences Notice what happens
when a single letter in the first sentence is changed
THE DOG BIT THE CATTHE DOG BIT THE CAR
As you can see changing a singleletter changes the meaning of theabove sentence Similarly a change ina single nitrogenous base can changethe entire structure of a proteinbecause a change in a single aminoacid can affect the shape of the pro-tein Figure 1111A shows what canhappen with a point mutation
Frameshift mutationsWhen the ribosome moves along
the mRNA strand a new amino acid is added to the protein for every codon on the mRNA strand What would happen if a single base were lost from a DNA strand
298 DNA AND GENES
Figure 1111The results of a pointmutation and aframeshift mutationare different The dia-grams show the mRNAand protein that wouldbe formed from eachcorresponding DNAInfer Which type ofmutation is likely tocause greater geneticdamage
Proteins that are produced as a result of frameshift mutations seldom functionproperly because such mutations usually change many amino acids Adding ordeleting one base of a DNA molecule will change nearly every amino acid in theprotein after the addition or deletion
BB
In this point mutation the mRNA produced by the mutated DNA had the baseguanine changed to adenine This change in the codon caused the insertion ofserine rather than glycine into the growing amino acid chain The error may ormay not interfere with protein function
AA
Normal
Pointmutation
Frameshiftmutation
AC AUGUGA U G A A G U U U G G C U AmRNA
StopMet Lys Phe Gly Ala LeuProtein
mRNA
StopMet Lys Phe Ser Ala LeuProtein
A AC UGUGA U G A A G U U U U AG C
Replace G with A
A
mRNA
Met Lys Leu Ala His CysProtein
G AC AAUGUGA U G A G U U G C U
UDeletion of U
A
0296-0307 C11S3 BDOL-829900 8304 1124 PM Page 298
113 GENETIC CHANGES 299
This new sequence with the deletedbase would be transcribed into mRNABut then the mRNA would be out ofposition by one base As a resultevery codon after the deleted basewould be different as shown inFigure 1111B This mutation wouldcause nearly every amino acid in theprotein after the deletion to bechanged In the sentence THE DOGBIT THE CAT deleting a G wouldproduce the sentence THE DOBITT HEC AT The same effect wouldresult from the addition of a singlebase A mutation in which a singlebase is added to or deleted from DNAis called a frameshift mutationbecause it shifts the reading of codonsby one base In general point muta-tions are less harmful to an organismbecause they disrupt only a single co-don The MiniLab on the next pagewill help you distinguish point muta-tions from frameshift mutations andthe Problem-Solving Lab on this pagewill show you an example of a com-mon mutation in humans
Compare and contrast the cause and effect of a point mutation and a frameshiftmutation
ChromosomalAlterations
Changes may occur in chromo-somes as well as in genes Alterationsto chromosomes may occur in a vari-ety of ways For example sometimesparts of chromosomes are broken offand lost during mitosis or meiosisOften chromosomes break and thenrejoin incorrectly Sometimes theparts join backwards or even join tothe wrong chromosome These struc-tural changes in chromosomes arecalled chromosomal mutations
Chromosomal mutations occur inall living organisms but they areespecially common in plants Suchmutations affect the distribution ofgenes to the gametes during meiosisHomologous chromosomes do notpair correctly when one chromosomehas extra or missing parts so separa-tion of the homologous chromosomesdoes not occur normally Gametesthat should have a complete set ofgenes may end up with extra copies ora complete lack of some genes
Make and Use TablesWhat type of mutation results in sickle-cell anemiaA disorder called sickle-cell anemia results from a genetic changein the base sequence of DNA Red blood cells in patients withsickle-cell anemia have molecules of hemoglobin that are mis-shapen As a result of this change in protein shape sickled bloodcells clog capillaries and prevent normal flow of blood to bodytissues causing severe pain
Solve the ProblemThe table below shows the sequence of bases in a short seg-ment of the DNA that controls the order of amino acids in theprotein hemoglobin
Thinking Critically1 Interpret Data Use Table 111 on page 292 to transcribe
and translate the DNA base sequence for normal hemo-globin and for sickled hemoglobin into amino acidsRemember that the table lists mRNA codons not DNAbase sequences
2 Define Operationally Does this genetic change illustratea point mutation or frameshift mutation Explain youranswer
3 Explain Why is the correct sequence of DNA bases impor-tant to the production of proteins
4 Analyze Assume that the base sequence reads GGG CTTCTT AAA instead of the normal sequence for hemoglobinWould this result in sickled hemoglobin Explain
DNA Base Sequences
Normal hemoglobin GGG CTT CTT TTT
Sickled hemoglobin GGG CAT CTT TTT
0296-0307 C11S3 BDOL-829900 8304 1125 PM Page 299
300 DNA AND GENES
A B C D E F G H A B C E F G H
A B C D E F G H A B C B C D E F G H
A B C D E F G H A D C B E F G H
A B C D E F G H W X A B C D E F G H
TranslocationW X Y Z Y Z
Deletion
Insertion
Inversion
Figure 1112Study the four kinds of chromosomalmutations
When a part of a chromosomeis left out a deletion occurs
A
When part of a chromatid breaksoff and attaches to its sisterchromatid an insertion occursThe result is a duplication ofgenes on the same chromosome
B
When part of a chromosomebreaks off and reattachesbackwards an inversion occurs
C
When part of one chromosomebreaks off and is added to adifferent chromosome atranslocation occurs
D
Few chromosomal mutations arepassed on to the next generationbecause the zygote usually dies In caseswhere the zygote lives and developsthe mature organism is often sterile andthus incapable of producing offspringThe most important of these muta-tionsmdashdeletions insertions inversionsand translocationsmdashare illustrated inFigure 1112
Causes of MutationsSome mutations seem to just hap-
pen perhaps as a mistake in basepairing during DNA replicationThese mutations are said to be spon-taneous However many mutationsare caused by factors in the environ-ment Any agent that can cause achange in DNA is called a mutagen(MYEW tuh jun) Mutagens includeradiation chemicals and even hightemperatures
Forms of radiation such as X rayscosmic rays ultraviolet light and
Make and Use TablesGene Mutations and ProteinsGene mutations often have seriouseffects on proteins In this activityyou will demonstrate how suchmutations affect protein synthesis
Procedure Copy the following base sequence of one strand of an
imaginary DNA molecule AATGCCAGTGGTTCGCAC Then write the base sequence for an mRNA strand that
would be transcribed from the given DNA sequence Use Table 111 to determine the sequence of amino acids
in the resulting protein fragment$ If the fourth base in the original DNA strand were
changed from G to C how would this affect the resultingprotein fragment
If a G were added to the original DNA strand after thethird base what would the resulting mRNA look like Howwould this addition affect the protein
Analysis1 Define Operationally Which change in DNA was a point
mutation Which was a frameshift mutation2 Infer How did the point mutation affect the protein3 Analyze How did the frameshift mutation affect the
protein
DNA segment
0296-0307 C11S3 BDOL-829900 8304 1125 PM Page 300
nuclear radiation are dangerous muta-gens because the energy they containcan damage or break apart DNA Thebreaking and reforming of a double-stranded DNA molecule can result indeletions Some kinds of radiation canconvert a base into a different incor-rect base or fuse two bases together
Chemical mutagens include diox-ins asbestos benzene and formalde-hyde substances that are commonlyfound in buildings and in the environ-ment Figure 1113 These mutagensare highly reactive substances thatinteract with the DNA molecule andcause changes Chemical mutagensusually cause substitution mutations
Repairing DNAThe cell processes that copy
genetic material and pass it from onegeneration to the next are usuallyaccurate This accuracy is importantto ensure the genetic continuity ofboth new cells and offspring Yetmistakes sometimes do occur Thereare many sources of mutagens in anorganismrsquos environment Althoughmany of these are due to humanactivities othersmdashsuch as cosmicrays from outer spacemdashhave affectedliving things since the beginning oflife Repair mechanisms that fixmutations in cells have evolved
Much like a book editor enzymesproofread the DNA and replaceincorrect nucleotides with correctnucleotides These repair mecha-nisms work extremely well but theyare not perfect The greater theexposure to a mutagen such as UVlight the more likely is the chancethat a mistake will not be correctedThus it is wise for people to limittheir exposure to mutagens
Understanding Main Ideas1 What is a mutation2 Describe how point mutations and frameshift
mutations affect the synthesis of proteins3 Explain why a mutation in a sperm or egg cell has
different consequences than one in a heart cell4 How are mutations and cancer related
Thinking Critically5 The chemicals in cigarette smoke are known to
cause cancer Propose a series of steps that couldlead to development of lung cancer in a smoker
6 Recognize Cause and Effect In an experimentwith rats the treatment group is exposed to radi-ation while the control group is not Months laterthe treatment group has a greater percentage of rats with cancer and more newborn rats withbirth defects than the control group Explain howthe exposure to radiation may have affected thetreatment grouprsquos DNA Infer how these effectscould have caused cancer and birth defects Formore help refer to Recognize Cause and Effect inthe Skill Handbook
SKILL REVIEWSKILL REVIEW
113 GENETIC CHANGES 301Tom TracyThe Stock ShopMedichrome
Figure 1113Asbestos was formerlyused to insulate build-ings It is now knownto cause lung cancerand other lung diseasesand must be removedfrom buildings as theseworkers are doing
ncbdolglencoecomself_check_quiz
0296-0307 C11S3 BDOL-829900 8304 1126 PM Page 301
302 DNA AND GENES
Before You BeginAlthough DNA remains inthe nucleus of a cell itpasses its information intothe cytoplasm by way ofanother nucleic acid mes-senger RNA The basesequence of this mRNA iscomplementary to thesequence in the strand ofDNA It is produced bybase pairing during tran-scription In this activityyou will demonstrate theprocess of transcriptionthrough the use of paperDNA and mRNA models
Adenine
Deoxyribose
Parts for DNA Nucleotides Extra Parts for RNANucleotides
Phosphate
Ribose
Phosphate
Guanine
Uracil
Thymine
Cytosine
RNA Transcription
ProblemHow does the order of bases in DNA determine the order ofbases in mRNA
ObjectivesIn this BioLab you will Formulate a model to show how the order of bases in
DNA determines the order of bases in mRNA Infer why the structure of DNA enables it to be easily
transcribed
Materialsconstruction paper 5 colorsscissorsclear tape
Safety PrecautionsCAUTION Be careful when using scissors Always use gogglesin the lab
Skill HandbookIf you need help with this lab refer to the Skill Handbook
PREPARATIONPREPARATION
0296-0307 C11S3 BDOL-829900 8304 1129 PM Page 302
113 GENETIC CHANGES 303
1 Copy the parts for the four different DNA nucleotidesonto your construction paper making sure that each dif-ferent nucleotide is on a different color paper Make tencopies of each nucleotide
2 Using scissors carefully cut out the shapes of eachnucleotide
3 Using any order of nucleotides that you wish construct adouble-stranded DNA molecule If you need morenucleotides copy them as in step 1
4 Fasten your molecule together using clear tape Do nottape across base pairs
5 As in step 1 copy the parts for A G and C RNA nucleo-tides Use the same colors of construction paper as instep 1 Use the fifth color of construction paper to makecopies of uracil nucleotides
6 With scissors carefully cut out the RNA nucleotideshapes
7 With your DNA molecule in front of you demonstratethe process of transcription by first pulling the DNAmolecule apart between the base pairs
8 Using only one of the strands of DNA begin matchingcomplementary RNA nucleotides with the exposed baseson the DNA model to make mRNA
9 When you are finished tape your new mRNA moleculetogether
PROCEDUREPROCEDURE
ANALYZE AND CONCLUDEANALYZE AND CONCLUDE
1 Observe and Infer Does the mRNA model more closely resemble theDNA strand from which it was transcribed or the complementary strandthat wasnrsquot used Explain your answer
2 Recognize Cause and Effect Explain howthe structure of DNA enables the moleculeto be easily transcribed Why is this impor-tant for genetic information
3 Relate Concepts Why is RNA important tothe cell How does an mRNA molecule carryinformation from DNA Where does themRNA molecule take the information
Research Do research to find out moreabout how the bases in DNA were identifiedand how the base pairing pattern was determined
Web Links To find out more aboutDNA visit
Matt Meadows
ncbdolglencoecomDNA
0296-0307 C11S3 BDOL-829900 8304 1132 PM Page 303
Scanning ProbeMicroscopes
Have you ever heard of someone dissecting achromosome to get a closer look at DNA
Imagine an instrument small enough to allowyou to grab hold of one of the nucleotides in astrand of DNA yet powerful enough to providea detailed image
Scanning probe microscopes can show thearrangement of atoms on the surface of a mole-cule They make it possible for scientists to pickup molecules and even atoms and move themaround They can also be used to observe howbiological molecules interact There are manytypes of scanning probe microscopes All ofthem use a very sharp probe that may be only asingle atom wide at its tip The probe sits veryclose to the specimen but does not actuallytouch it As the probe moves across or scansthe specimen it measures some property of thespecimen
The scanning tunneling microscope (STM)The STM uses a probe through which a tinyamount of electric current flows As the probescans a molecule it encounters ridges and val-leys formed by the different kinds of atoms onthe moleculersquos surface The probe moves upand down as needed to keep the current con-stant The movements of the probe arerecorded by a computer which produces animage of the molecule
The atomic force microscope (AFM) TheAFM can measure many different propertiesincluding electricity magnetism and heat Asthe probe moves across the specimen changes inthe property being measured move the probeThese changes are used to create the image
What can they do One of the primary advan-tages of scanning probe microscopy besides itsatomic-level resolution is the ability to observe
molecules in air or liquid This means that biol-ogists can ldquowatchrdquo molecules interact as theywould inside a cell
Scanning probe microscopes are being used tostudy patterns in liquid crystals wave convec-tion molecular surfaces of materials and molec-ular events such as the function of bacterialtoxins and ion channels actin and myosin inter-actions in muscle cells and protein folding
Imaging transcription Biologists currentlyare imaging factors that are involved in the tran-scription of DNA These factors includeenzymes that cut DNA and those that repairDNA errors By using the AFM biologists arebeginning to identify the DNA binding sites forthese enzymes which will be used in mappingstudies of DNA This will allow further under-standing of the process of transcription
Think Critically What advantages do scanningprobe microscopes have over other types of micro-scopes Predict some future applications that wouldmake use of these advantages
To find out more about microscopes visit
Magnification unavailable
304 DNA AND GENES
STM image of DNA
ncbdolglencoecombiotechnology
Photo Researchers
0296-0307 C11S3 BDOL-829900 8304 1133 PM Page 304
Section 111STUDY GUIDESTUDY GUIDE
CHAPTER 11 ASSESSMENT 305Dr Gopal MurtiScience Photo LibraryPhoto Researchers
To help you reviewDNA use the Organizational StudyFold on page 288
Color-enhanced TEMMagnification 75 000
Key Concepts Alfred Hershey and Martha Chase demon-
strated that DNA is the genetic material DNA the genetic material of organisms
is composed of four kinds of nucleotides A DNA molecule consists of two strands of nucleotides with sugars and phosphateson the outside and bases paired by hydro-gen bonding on the inside The pairedstrands form a twisted-zipper shape calleda double helix
Because adenine can pair only withthymine and guanine can pair only withcytosine DNA can replicate itself withgreat accuracy
VocabularyDNA replication (p 284)double helix (p 283)nitrogenous base
(p 282)
DNA TheMolecule ofHeredity
Key Concepts Genes are small sections of DNA Most
sequences of three bases in the DNA of a gene code for a single amino acid in aprotein
Messenger RNA is made in a processcalled transcription The order ofnucleotides in DNA determines the orderof nucleotides in messenger RNA
Translation is a process through which theorder of bases in messenger RNA codes forthe order of amino acids in a protein
Vocabularycodon (p 292)messenger RNA (p 289)ribosomal RNA (p 290)transcription (p 290)transfer RNA (p 290)translation (p 293)
From DNA toProtein
Section 112
Key Concepts A mutation is a change in the base
sequence of DNA Mutations may affectonly one gene or they may affect wholechromosomes
Mutations in eggs or sperm affect futuregenerations by producing offspring withnew characteristics Mutations in bodycells affect only the individual and mayresult in cancer
Vocabularychromosomal mutation
(p 299)frameshift mutation
(p 299)mutagen (p 300)mutation (p 296)point mutation (p 298)
GeneticChanges
Section 113
ncbdolglencoecomvocabulary_puzzlemaker
0296-0307 C11S3 BDOL-829900 8304 1135 PM Page 305
Review the Chapter 11 vocabulary words listed inthe Study Guide on page 305 Distinguish betweenthe vocabulary words in each pair below
1 transcriptionmdashtranslation2 point mutationmdashframeshift mutation3 transfer RNAmdashmessenger RNA4 mutationmdashmutagen5 nitrogenous basemdashcodon
6 Which of the following processes requiresprior DNA replicationA transcription C mitosisB translation D protein synthesis
7 In which of the following processes does theDNA unzipA transcription and translationB transcription and replicationC replication and translationD mutation
8 Which DNA strand can base pair with the DNA strandshown at the rightA T-A-C-G-A-T C U-A-C-G-A-UB A-T-G-C-T-A D A-U-G-C-U-A
9 Which of the following nucleotide chainscould be part of a molecule of RNAA A-T-G-C-C-A C G-C-C-T-T-GB A-A-T-A-A-A D A-U-G-C-C-A
10 Which of the following mRNA codonswould cause synthesis of a protein to termi-nate Refer to Table 111A GGG C UAGB UAC D AAG
11 The genetic code for an oak tree is ________A more similar to an ash tree than to a squirrelB more similar to a chipmunk than to a
maple treeC more similar to a mosquito than to an
elm treeD exactly the same as for an octopus
12 A deer is born normal but UV rays cause amutation in its retina Which of the follow-ing statements is least likely to be trueA The mutation may be passed on to the
offspring of the deerB The mutation may cause retinal cancerC The mutation may interfere with the
function of the retinal cellD The mutation may interfere with the
structure of the retinal cell
13 Chemical Q causes the change in thesequence of nucleotides shown below Thischange is an example of a(n) ________ A point mutationB frameshift mutationC translocationD inversion
14 Open Ended Explain why a mutation in a lung cell would not be passed on to offspring
15 Open Ended Write the sequence for a seg-ment of DNA that codes for the followingchain of amino acids valine-serine-proline-glycine-leucine Compare your DNAsequence with another studentrsquos sequenceWhy are they likely to be different
16 Open Ended Would the amount of cytosineand guanine be equal to each other in anRNA molecule Explain your answer
17 Make Inferences Explain how the univer-sality of the genetic code is evidence that allorganisms alive today may have evolvedfrom a common ancestor in the past
TAA T G AA T A AA A
AA TT G C
306 CHAPTER 11 ASSESSMENT ncbdolglencoecomchapter_test
0296-0307 C11S3 BDOL-829900 8304 1135 PM Page 306
18 Summarize Using the diagram to the right describe the way DNA replicatesRefer to the red and bluestrands in your answer
19 Cystic fibrosisis an inherited genetic disorder that affectsabout 1 in 3900 live births of all AmericansVisit to find out whattype of changes in DNA cause this disorderHow are these changes reflected in thesymptoms of the disorder
REAL WORLD BIOCHALLENGE
CHAPTER 11 ASSESSMENT 307
ncbdolglencoecom
Multiple ChoiceUse the diagram to answer questions 20ndash22
20 What process is shown in diagrams AndashCA transcription C translocationB translation D replication
21 What occurred between diagrams A and BA DNA was copiedB DNA was translatedC DNA was unzippedD DNA mutated
22 What structure is represented by the circlemarked ldquoXrdquoA nitrogenous base C nucleotideB deoxyribose D phosphate group
The following graph records the amount of DNA inliver cells that have been grown in a culture so thatall the cells are at the same phase in the cell cycleStudy the graph and answer questions 23 and 24
23 What process are the cells undergoing atpart A of the graph to cause the observedchange in DNA contentA transcriptionB translationC DNA replicationD meiosis
24 During what part of the graph is translationmost likely to occurA at part AB at part BC at part CD at both part A and part C
Change in DNA Content Per Cell
DN
A (
pic
og
ram
sce
ll)
Time (hours)
01
0
02
03
04
05
06
2 6 10 14 18 22 26
A
C
B
X
A
B
C
A T
G
G
C
C
A T
G
G
C
C
A T
G
G
C
C
A T
G
G
C
C
A T
G
G
C
C
Constructed ResponseGrid InRecord your answers on your answer document
25 Open Ended A point mutation that doesnrsquot change the amino acid sequence of a protein is knownas a silent mutation Explain why a silent mutation might not affect the protein for which it codes
The assessed North Carolina objective appears next to the question
ncbdolglencoecomstandardized_test
301
301
201
301
301
0296-0307 C11S3 BDOL-829900 8304 1137 PM Page 307
- Biology The Dynamics of LifemdashNorth Carolina Edition
-
- Contents in Brief
-
- The North Carolina Biology Handbook
-
- Correlations to the North Carolina Objectives
-
- North Carolina Objectives to Biology The Dynamics of Life
- Biology The Dynamics of Life to North Carolina Objectives
-
- How to Master the North Carolina Objectives
- End-of-Course Test Practice Countdown
-
- Table of Contents
-
- Unit 1 What is biology
-
- Chapter 1 Biology The Study of Life
-
- Section 11 What is biology
-
- MiniLab 11 Predicting Whether Mildew Is Alive
- Careers in Biology Nature Preserve Interpreter
-
- Section 12 The Methods of Biology
-
- MiniLab 12 Testing for Alcohol
- Problem-Solving Lab 11
- Inside Story Scientific Methods
-
- Section 13 The Nature of Biology
-
- Problem-Solving Lab 12
- MiniLab 13 Hatching Dinosaurs
- Internet BioLab Collecting Biological Data
- Biology and Society Organic Food Is it healthier
-
- Chapter 1 Assessment
-
- BioDigest What is biology
- Unit 1 Standardized Test Practice
-
- Unit 2 Ecology
-
- Chapter 2 Principles of Ecology
-
- Section 21 Organisms and Their Environment
-
- MiniLab 21 Salt Tolerance of Seeds
- Problem-Solving Lab 21
- Careers in Biology Science Reporter
-
- Section 22 Nutrition and Energy Flow
-
- Problem-Solving Lab 22
- Physical Science Connection Conservation of Energy
- Physical Science Connection Conservation of Mass
- MiniLab 22 Detecting Carbon Dioxide
- Inside Story The Carbon Cycle
- Design Your Own BioLab How can one population affect another
- Biology and Society The EvergladesmdashRestoring an Ecosystem
-
- Chapter 2 Assessment
-
- Chapter 3 Communities and Biomes
-
- Section 31 Communities
-
- MiniLab 31 Looking at Lichens
- Problem-Solving Lab 31
-
- Section 32 Biomes
-
- Physical Science Connection Salinity and Density of a Solution
- Problem-Solving Lab 32
- MiniLab 32 Marine Plankton
- Inside Story A Tropical Rain Forest
- Investigate BioLab Succession in a Jar
- Connection to Literature Our National Parks by John Muir
-
- Chapter 3 Assessment
-
- Chapter 4 Population Biology
-
- Section 41 Population Dynamics
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- MiniLab 41 Fruit Fly Population Growth
- Inside Story Population Growth
- Problem-Solving Lab 41
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- Section 42 Human Population
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- Problem-Solving Lab 42
- MiniLab 42 Doubling Time
- Investigate BioLab How can you determine the size of an animal population
- Connection to Chemistry Polymers for People
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- Chapter 4 Assessment
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- Chapter 5 Biological Diversity and Conservation
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- Section 51 Vanishing Species
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- MiniLab 51 Field Investigation
- Problem-Solving Lab 51
- Physical Science Connection Environmental Impact of Generating Electricity
- Physical Science Connection Wave Energy
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- Section 52 Conservation of Biodiversity
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- MiniLab 52 Conservation of Soil
- Problem-Solving Lab 52
- Internet BioLab Researching Information on Exotic Pets
- Connection to Art Photographing Life
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- Chapter 5 Assessment
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- BioDigest Ecology
- Unit 2 Standardized Test Practice
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- Unit 3 The Life of a Cell
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- Chapter 6 The Chemistry of Life
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- Section 61 Atoms and Their Interactions
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- Problem-Solving Lab 61
- Physical Science Connection Chemical Bonding and the Periodic Table
- Physical Science Connection Conservation of Mass in Chemical Reactions
- Careers in Biology WeedPest Control Technician
- MiniLab 61 Determine pH
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- Section 62 Water and Diffusion
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- Physical Science Connection The Structure of Water Molecules
- Physical Science Connection Density of Liquids
- Problem-Solving Lab 62
- MiniLab 62 Investigate the Rate of Diffusion
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- Section 63 Life Substances
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- Inside Story Action of Enzymes
- Design Your Own BioLab Does temperature affect an enzyme reaction
- BioTechnology The Good News and the Bad News About Cholesterol
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- Chapter 6 Assessment
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- Chapter 7 A View of the Cell
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- Section 71 The Discovery of Cells
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- Physical Science Connection Lenses and the Refraction of Light
- MiniLab 71 Measuring Objects Under a Microscope
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- Section 72 The Plasma Membrane
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- Problem-Solving Lab 71
- Physical Science Connection Solubility and the Nature of Solute and Solvent
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- Section 73 Eukaryotic Cell Structure
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- Problem-Solving Lab 72
- MiniLab 72 Cell Organelles
- Physical Science Connection Conservation of Energy
- Inside Story Comparing Animal and Plant Cells
- Investigate BioLab Observing and Comparing Different Cell Types
- Connection to Literature The Lives of a Cell by Lewis Thomas
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- Chapter 7 Assessment
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- Chapter 8 Cellular Transport and the Cell Cycle
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- Section 81 Cellular Transport
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- MiniLab 81 Cell Membrane Simulation
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- Section 82 Cell Growth and Reproduction
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- Problem-Solving Lab 81
- Problem-Solving Lab 82
- Inside Story Chromosome Structure
- MiniLab 82 Seeing Asters
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- Section 83 Control of the Cell Cycle
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- Problem-Solving Lab 83
- Investigate BioLab Where is mitosis most common
- Connection to Health Skin Cancer
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- Chapter 8 Assessment
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- Chapter 9 Energy in a Cell
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- Section 91 The Need for Energy
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- Problem-Solving Lab 91
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- Section 92 Photosynthesis Trapping the Suns Energy
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- MiniLab 91 Separating Pigments
- MiniLab 92 Use Isotopes to Understand Photosynthesis
- Inside Story The Calvin Cycle
- Biotechnology Careers Biochemist
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- Section 93 Getting Energy to Make ATP
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- Inside Story The Citric Acid Cycle
- Problem-Solving Lab 92
- MiniLab 93 Determine if Apple Juice Ferments
- Internet BioLab What factors influence photosynthesis
- Connection to Chemistry Plant Pigments
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- Chapter 9 Assessment
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- BioDigest The Life of a Cell
- Unit 3 Standardized Test Practice
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- Unit 4 Genetics
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- Chapter 10 Mendel and Meiosis
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- Section 101 Mendels Laws of Heredity
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- MiniLab 101 Looking at Pollen
- Problem-Solving Lab 101
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- Section 102 Meiosis
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- Problem-Solving Lab 102
- MiniLab 102 Modeling Crossing Over
- Inside Story Chromosome Mapping
- Internet BioLab How can phenotypes and genotypes of plants be determined
- Connection to Math A Solution from Ratios
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- Chapter 10 Assessment
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- Chapter 11 DNA and Genes
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- Section 111 DNA The Molecule of Heredity
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- Problem-Solving Lab 111
- Inside Story Copying DNA
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- Section 112 From DNA to Protein
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- Problem-Solving Lab 112
- MiniLab 111 Transcribe and Translate
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- Section 113 Genetic Changes
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- Physical Science Connection Gamma Radiation as a Wave
- Careers in Biology Genetic Counselor
- Problem-Solving Lab 113
- MiniLab 112 Gene Mutations and Proteins
- Investigate BioLab RNA Transcription
- BioTechnology Scanning Probe Microscopes
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- Chapter 11 Assessment
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- Chapter 12 Patterns of Heredity and Human Genetics
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- Section 121 Mendelian Inheritance of Human Traits
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- MiniLab 121 Illustrating a Pedigree
- Problem-Solving Lab 121
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- Section 122 When Heredity Follows Different Rules
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- Problem-Solving Lab 122
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- Section 123 Complex Inheritance of Human Traits
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- Inside Story The ABO Blood Group
- Problem-Solving Lab 123
- MiniLab 122 Detecting Colors and Patterns in Eyes
- Design Your Own BioLab What is the pattern of cytoplasmic inheritance
- Connection to Social Studies Queen Victoria and Royal Hemophilia
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- Chapter 12 Assessment
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- Chapter 13 Genetic Technology
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- Section 131 Applied Genetics
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- Problem-Solving Lab 131
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- Section 132 Recombinant DNA Technology
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- MiniLab 131 Matching Restriction Enzymes to Cleavage Sites
- Inside Story Gel Electrophoresis
- Problem-Solving Lab 132
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- Section 133 The Human Genome
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- MiniLab 132 Storing the Human Genome
- Biotechnology Careers Forensic Analyst
- Problem-Solving Lab 133
- Investigate BioLab Modeling Recombinant DNA
- BioTechnology New Vaccines
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