powerlecture: chapter 22 dna, genes, and biotechnology

PowerLecture:PowerLecture:Chapter 22Chapter 22

DNA, Genes, and DNA, Genes, and BiotechnologyBiotechnology

Learning ObjectivesLearning Objectives

Understand how the instructions for Understand how the instructions for producing heritable traits are encoded in producing heritable traits are encoded in DNA.DNA.

Know the parts of a nucleotide, and know Know the parts of a nucleotide, and know how nucleotides are linked together to make how nucleotides are linked together to make DNA.DNA.

Understand how DNA is replicated and Understand how DNA is replicated and what materials are needed for replication.what materials are needed for replication.

Know how the structure and behavior of Know how the structure and behavior of DNA determine the structure and behavior DNA determine the structure and behavior of the forms of RNA during transcription.of the forms of RNA during transcription.

Learning Objectives (cont’d)Learning Objectives (cont’d)

Know how the structure and behavior of the Know how the structure and behavior of the three forms of RNA determine the primary three forms of RNA determine the primary structure of polypeptide chains during structure of polypeptide chains during translation.translation.

Know the various ways that gene activity Know the various ways that gene activity (replication and transcription) are turned on (replication and transcription) are turned on (activated) and off (inactivated).(activated) and off (inactivated).

Understand what plasmids are and how Understand what plasmids are and how they may be used to insert new genes into they may be used to insert new genes into recombinant DNA molecules.recombinant DNA molecules.

Learning Objectives (cont’d)Learning Objectives (cont’d)

Know how DNA can be cleaved, spliced, Know how DNA can be cleaved, spliced, cloned, and sequenced.cloned, and sequenced.

Be aware of several limits and possibilities Be aware of several limits and possibilities for future research in genetic engineering. for future research in genetic engineering.

Impacts/IssuesImpacts/Issues

Ricin and Ricin and Your RibosomesYour Ribosomes

Ricin and Your Ribosomes Ricin and Your Ribosomes

Ricin could be used as a biochemical weapon.Ricin could be used as a biochemical weapon. Ricin was identified as a biochemical weapon as long Ricin was identified as a biochemical weapon as long

ago as the 1880s and was considered for use during ago as the 1880s and was considered for use during WWII by both the US and England.WWII by both the US and England.

It is a poisonous byproduct formed during It is a poisonous byproduct formed during

production of castor oil from the castor bean.production of castor oil from the castor bean. Ricin inactivates ribosomes by damaging the part Ricin inactivates ribosomes by damaging the part

of the ribosome where amino acids are joined of the ribosome where amino acids are joined together; protein synthesis stops and the person together; protein synthesis stops and the person dies because there is no antidote.dies because there is no antidote.

How Would You Vote?How Would You Vote?To conduct an instant in-class survey using a classroom response To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main system, access “JoinIn Clicker Content” from the PowerLecture main menu. menu.

Given the threat of biochemical warfare, Given the threat of biochemical warfare, would you be willing to be vaccinated – or would you be willing to be vaccinated – or does the threat seem too remote?does the threat seem too remote? a. Yes, serious bioterror threats can be lethal in a. Yes, serious bioterror threats can be lethal in

small doses and easy to manufacture.small doses and easy to manufacture. b. No, we must be selective in what diseases to b. No, we must be selective in what diseases to

vaccinate against. vaccinate against.

Section 1Section 1

DNA: A Double HelixDNA: A Double Helix

DNA: A Double Helix DNA: A Double Helix

DNA is built of four kinds of nucleotides.DNA is built of four kinds of nucleotides. Each Each nucleotidenucleotide consists of a five-carbon consists of a five-carbon

sugar (deoxyribose), a phosphate group, and sugar (deoxyribose), a phosphate group, and one of four bases—adenine (A), guanine (G), one of four bases—adenine (A), guanine (G), thymine (T), cytosine (C).thymine (T), cytosine (C).

Figure 22.1Figure 22.1

Fig 22.1b, p.406

sugar(deoxyribose)

adenineA

base with adouble-ring

structure

guanineG

base with adouble-ring

structure

thymineT

base with asingle-ringstructure

cytosineC

base with asingle-ringstructure


Watson and Crick were the first to discover the Watson and Crick were the first to discover the structure of DNA.structure of DNA.

• DNA consists of two strands of nucleotides twisted into DNA consists of two strands of nucleotides twisted into a double helix.a double helix.

• Nucleotides are joined along the molecule’s length by Nucleotides are joined along the molecule’s length by covalent bonds and run in opposite directions; the two covalent bonds and run in opposite directions; the two strands are held together with weaker hydrogen bonds.strands are held together with weaker hydrogen bonds.


Fig 22.2, p.407

The pattern of base pairing (A only with T and G only with C) is consistent with the known composition of DNA (A=T and G=C


Chemical “rules” determine which Chemical “rules” determine which nucleotide bases in DNA can pair up.nucleotide bases in DNA can pair up.

Base pairsBase pairs are formed by the hydrogen are formed by the hydrogen bonding of A with T, and G with C.bonding of A with T, and G with C.

In a DNA molecule, the amount of adenine In a DNA molecule, the amount of adenine always equals thymine, and G = C.always equals thymine, and G = C.

The base pairs can occur in any sequence The base pairs can occur in any sequence along the length of the DNA molecule.along the length of the DNA molecule.


A gene is a sequence of nucleotides.A gene is a sequence of nucleotides. A A genegene is a sequence of nucleotides in a DNA is a sequence of nucleotides in a DNA

molecule.molecule. The The nucleotide sequencenucleotide sequence of each gene codes of each gene codes

for a given polypeptide chain.for a given polypeptide chain.


Section 2Section 2

Passing on Passing on Genetic InstructionsGenetic Instructions

How is a DNA molecule duplicated?How is a DNA molecule duplicated? DNA replicationDNA replication is the process that duplicates is the process that duplicates

DNA before a cell divides.DNA before a cell divides.• First, the two strands of DNA unwind and expose First, the two strands of DNA unwind and expose

their bases to serve as a template.their bases to serve as a template.• Then, unattached nucleotides are linked by Then, unattached nucleotides are linked by

hydrogen bonds to exposed bases according to hydrogen bonds to exposed bases according to base pairing rules.base pairing rules.

Replication results in DNA molecules each Replication results in DNA molecules each consisting of one “old” strand and one “new” consisting of one “old” strand and one “new” strand—strand—semiconservativesemiconservative replicationreplication..

Passing on Genetic Instructions Passing on Genetic Instructions

Fig 22.4, p.408

A. Parent DNA molecule, two complimentary strands of base-paired nucleotides.

B. Replication begin; the two strands unwind and separate from each other at specific sites along the length of the DNA molecule.

C. Each “old” strand serves as a structural pattern (a template) for the addition of bases according to the base paring rule.

D. Bases positioned on each old strand are joined together into a “new” strand. Each half-old, half new DNA molecule is just like the parent molecule

Mistakes and damage in DNA can be Mistakes and damage in DNA can be repaired.repaired.

DNA polymerases and other enzymes are DNA polymerases and other enzymes are involved in involved in DNA repairDNA repair mechanisms. mechanisms.

• These enzymes detect and correct the sequence of These enzymes detect and correct the sequence of bases if it becomes altered; they do so by reading bases if it becomes altered; they do so by reading the complementary sequence on the other strand the complementary sequence on the other strand and restoring it.and restoring it.

• If an error is not fixed, a mutation results.If an error is not fixed, a mutation results.


DNA is vulnerable to damage from chemicals DNA is vulnerable to damage from chemicals and UV light, which can form and UV light, which can form thymine dimersthymine dimers that increase replication errors.that increase replication errors.

Thymine dimers can lead to the genetic Thymine dimers can lead to the genetic disorder disorder xeroderma pigmentosumxeroderma pigmentosum, which , which further increases an individual’s chance of further increases an individual’s chance of developing lethal skin cancers.developing lethal skin cancers.



A mutation is a change in the sequence of A mutation is a change in the sequence of a gene’s nucleotides.a gene’s nucleotides.

Gene mutationsGene mutations are small-scale changes in are small-scale changes in the nucleotide sequence of genes.the nucleotide sequence of genes.

• Base-pair Base-pair substitutionssubstitutions can can result in the result in the substitution of one substitution of one amino acid for amino acid for another in a another in a protein, as in protein, as in sickle-cell anemia.sickle-cell anemia.


Figure 22.6a-bFigure 22.6a-b

• A A deletiondeletion occurs when a base has been lost. occurs when a base has been lost.

• In an In an expansion mutationexpansion mutation, a nucleotide sequence , a nucleotide sequence is repeated many times, as in Huntington disease is repeated many times, as in Huntington disease and and fragile X syndromefragile X syndrome..


Figures 22.6a, c, and 22.7aFigures 22.6a, c, and 22.7a

NeurofibromatosisNeurofibromatosis is caused by segments of is caused by segments of DNA called DNA called transposable elementstransposable elements (in this (in this case, a specific element called Alu); such case, a specific element called Alu); such elements can move from location to location in elements can move from location to location in the chromosomes.the chromosomes.

Mutations are only inherited if they occur in the Mutations are only inherited if they occur in the germ cells that form the gametes.germ cells that form the gametes.


Figure 22.7bFigure 22.7b

Section 3Section 3

DNA into RNA—The First DNA into RNA—The First Step in Making ProteinsStep in Making Proteins

DNA into RNA—DNA into RNA—The First Step in Making Proteins The First Step in Making Proteins

Genes become proteins through the Genes become proteins through the processes of transcription and translation.processes of transcription and translation.

RNA is involved in both processes; RNA is RNA is involved in both processes; RNA is single-stranded, contains the sugar ribose, and single-stranded, contains the sugar ribose, and substitutes the base uracil for the thymine of substitutes the base uracil for the thymine of DNA.DNA.

• In In transcriptiontranscription, molecules of RNA are produced on , molecules of RNA are produced on the DNA templates in the nucleus.the DNA templates in the nucleus.

• In In translationtranslation, RNA molecules are shipped from the , RNA molecules are shipped from the nucleus to the cytoplasm to be used in polypeptide nucleus to the cytoplasm to be used in polypeptide assembly.assembly.


Genes are transcribed into three kinds of RNA:Genes are transcribed into three kinds of RNA:• Ribosomal RNARibosomal RNA (rRNA) combines with proteins to (rRNA) combines with proteins to

form ribosomes upon which polypep tides are form ribosomes upon which polypep tides are assembled.assembled.

• Messenger RNAMessenger RNA (mRNA) carries the protein “code” (mRNA) carries the protein “code” to the ribosome.to the ribosome.

• Transfer RNATransfer RNA (tRNA) brings the correct amino acid (tRNA) brings the correct amino acid to the ribosome and pairs up with an mRNA to the ribosome and pairs up with an mRNA nucleotide code for that amino acid.nucleotide code for that amino acid.


In transcription, DNA is decoded into RNA.In transcription, DNA is decoded into RNA. Transcription differs from replication in three Transcription differs from replication in three

ways:ways:• Only one region of one DNA strand is used as a Only one region of one DNA strand is used as a

template.template.• RNA polymeraseRNA polymerase is used instead of DNA is used instead of DNA

polymerase.polymerase.• The result of transcription is a single-stranded RNA.The result of transcription is a single-stranded RNA.

© 2007 Thomson Higher Education

DNA

DNA DNA

RNA

base-pairing in DNA replication base-pairing in transcription

In-text Fig, p.410


Transcription begins when RNA polymerase Transcription begins when RNA polymerase binds to a binds to a promoterpromoter region (a base sequence region (a base sequence at the start of a gene) and then moves along to at the start of a gene) and then moves along to the end of a gene.the end of a gene.

• The result is a RNA transcript, which will have a 5The result is a RNA transcript, which will have a 5 cap and a 3cap and a 3 tail. tail.

• The RNA is also modified: The RNA is also modified: intronsintrons (noncoding (noncoding portions of the RNA) are removed, and portions of the RNA) are removed, and exonsexons (those (those portions that will be translated) are stitched together portions that will be translated) are stitched together before the finished transcript leaves the nucleus.before the finished transcript leaves the nucleus.

Gene TranscriptionGene Transcription


[Step art][Step art]


Gene transcription can be turned on or off.Gene transcription can be turned on or off. Most of the cells of the human body carry the Most of the cells of the human body carry the

same genes, but only certain genes are same genes, but only certain genes are expressed in any given cell at any given time.expressed in any given cell at any given time.

Genes are turned on and off by Genes are turned on and off by regulatory regulatory proteinsproteins that speed up or halt transcription. that speed up or halt transcription.

Section 4Section 4

Reading the Reading the

Genetic CodeGenetic Code

Reading the Genetic Code Reading the Genetic Code

Codons are mRNA “words” for building Codons are mRNA “words” for building proteins.proteins.

Three base triplets, a Three base triplets, a codoncodon, specify each , specify each amino acid to be included into a growing amino acid to be included into a growing polypeptide chain.polypeptide chain.

The The genetic codegenetic code consists of a total of 64 consists of a total of 64 triplet codons: most specify amino acids, one is triplet codons: most specify amino acids, one is a a start codonstart codon (AUG) and three are (AUG) and three are stop stop codonscodons (UAA, UAG, UGA). (UAA, UAG, UGA).

Most amino acids can be specified by more Most amino acids can be specified by more than one codon. than one codon.

Fig 22.9, p.412

mRNAcodons

a

bthreonine proline glutamate glutamate lysine

DNA

mRNA

aminoacids

The Genetic The Genetic CodeCode



tRNA translates the genetic code.tRNA translates the genetic code. Each kind of tRNA has an Each kind of tRNA has an anticodonanticodon that is that is

complementary to an mRNA codon; each tRNA complementary to an mRNA codon; each tRNA also carries one specific amino acid.also carries one specific amino acid.



After the mRNA arrives in the cytoplasm, a After the mRNA arrives in the cytoplasm, a specific anticodon on a tRNA bonds to the specific anticodon on a tRNA bonds to the codon on the mRNA by complementary base-codon on the mRNA by complementary base-pairing, and so a correct amino acid is brought pairing, and so a correct amino acid is brought into place.into place.

There are fewer tRNAs than the number of There are fewer tRNAs than the number of possible codons because the third position in possible codons because the third position in the codon-anticodon pairing is loose; the the codon-anticodon pairing is loose; the wobble effectwobble effect allows some tRNAs to match allows some tRNAs to match multiple amino acids to the right codon.multiple amino acids to the right codon.


rRNAs are ribosome building blocks.rRNAs are ribosome building blocks. Translation occurs on the surface of ribosomes Translation occurs on the surface of ribosomes

where the tRNAs and mRNA interact.where the tRNAs and mRNA interact. Ribosomal subunits are synthesized from rRNA Ribosomal subunits are synthesized from rRNA

and proteins in the nucleus, then shipped to the and proteins in the nucleus, then shipped to the cytoplasm where they are combined into cytoplasm where they are combined into ribosomes during translation.ribosomes during translation.


Section 5Section 5

Translating the Genetic Translating the Genetic Code into ProteinCode into Protein

Translating the Genetic Code into Protein Translating the Genetic Code into Protein

Translation has three stages.Translation has three stages. In In initiationinitiation, a complex forms in this sequence: , a complex forms in this sequence:

initiator tRNA + small ribosomal subunit + initiator tRNA + small ribosomal subunit + mRNA (specifically, the AUG start codon) + mRNA (specifically, the AUG start codon) + large ribosomal subunit.large ribosomal subunit.

In In elongationelongation, the mRNA passes through the , the mRNA passes through the ribosome attracting a series of tRNAs that ribosome attracting a series of tRNAs that deliver amino acids in sequence by codon-deliver amino acids in sequence by codon-anticodon matching; a anticodon matching; a peptide bondpeptide bond joins each joins each amino acid to the next in the sequence.amino acid to the next in the sequence.

© 2007 Thomson Higher Education Fig. 22.13a-c, p.414

intact ribosome

INITIATION

mRNA transcript

Elongation

© 2007 Thomson Higher Education Fig. 22.13d-f, p.414

binding site for mRNA

(first bindingsite for tRNA)

(second bindingsite for tRNA)


Fig. 22.13f-i, p.415


With With terminationtermination, a stop codon is reached that , a stop codon is reached that has no corresponding tRNA; release factors has no corresponding tRNA; release factors cause the polypeptide chain and the mRNA to cause the polypeptide chain and the mRNA to be released. be released.


Cells use newly formed proteins in various Cells use newly formed proteins in various ways.ways.

To increase the efficiency of the translation To increase the efficiency of the translation process, several ribosomes can be aligned on process, several ribosomes can be aligned on one mRNA (one mRNA (polysomepolysome), allowing synthesis of ), allowing synthesis of more than one polypeptide at a time.more than one polypeptide at a time.

After new polypeptide chains are complete, After new polypeptide chains are complete, they may join the pool of proteins in the they may join the pool of proteins in the cytoplasm or may enter the ER for modification.cytoplasm or may enter the ER for modification.


mRNA rRNA tRNA

Translation amino acids, ribosome subunits, and tRNAs in the cytoplasm

maturemRNA

protein subunits

ribosomal subunits

maturetRNA

Transcription

FINAL PROTEIN

Fig 22.26, p.424

At ribosome, a polypeptide chain is synthesized at the binding sites for mRNA and tRNAs

RNAs converge

Transcriptprocessing:

Different gene regions of DNA:

For use in cell or for export

Section 6Section 6

Tools for Tools for “Engineering” Genes“Engineering” Genes

Tools for “Engineering” Genes Tools for “Engineering” Genes

Recombinant DNA technologyRecombinant DNA technology encompasses a range of techniques that encompasses a range of techniques that allow for the specific creation of genetic allow for the specific creation of genetic changes in DNA.changes in DNA.

DNA from different species can be cut, spliced DNA from different species can be cut, spliced together, and inserted into bacteria, which then together, and inserted into bacteria, which then multiply the multiply the recombinant DNArecombinant DNA molecules. molecules.

Genetic engineeringGenetic engineering involves the isolation, involves the isolation, modification, and reinsertion of DNA back into modification, and reinsertion of DNA back into an organism.an organism.


Enzymes and plasmids from bacteria are Enzymes and plasmids from bacteria are basic tools.basic tools.

Many bacteria possess Many bacteria possess plasmidsplasmids, circular DNA , circular DNA molecules that carry only a few genes and molecules that carry only a few genes and which can replicate independently of the single which can replicate independently of the single “main” chromosome.“main” chromosome.

Restriction enzymesRestriction enzymes are used by bacteria to are used by bacteria to cut apart DNA; this capability makes them cut apart DNA; this capability makes them useful to researchers as tools for doing useful to researchers as tools for doing genetic genetic recombinationrecombination in the laboratory. in the laboratory.


• Restriction enzymes produce DNA fragments with Restriction enzymes produce DNA fragments with staggered cuts resulting in staggered cuts resulting in sticky endssticky ends; some ; some fragments may be thousands of bases long, allowing fragments may be thousands of bases long, allowing the study of the the study of the genomegenome (all of the DNA in a haploid (all of the DNA in a haploid set of chromosomes).set of chromosomes).

• The sticky ends of the fragments can be spliced The sticky ends of the fragments can be spliced together by other enzymes to create a recombinant together by other enzymes to create a recombinant DNA molecule.DNA molecule.

Using these tools, it is possible to insert foreign Using these tools, it is possible to insert foreign DNA into bacterial plasmids, creating DNA into bacterial plasmids, creating DNA DNA clonesclones; DNA clones are sometimes called ; DNA clones are sometimes called cloning vectorscloning vectors. .


A. A selected restriction enzyme cuts wherever a specific base sequence occurs in a molecule of chromosomal DNA or cDNA.

F. A collection of recombinant plasmids containing foreign DNA.

G. Host cells able to divide rapidly take up recombinant plasmids.

B. The same enzyme cuts the same sequence in plasmid DNA.

E. The foreign DNA, the plasmid DNA, and modificationenzymes are mixed together.C. DNA or cDNA

fragments with sticky ends.

D. Plasmid DNA with sticky ends

Fig 22.14, p.416


The The polymerase chain reactionpolymerase chain reaction ( (PCRPCR) is a ) is a faster way to copy DNA. faster way to copy DNA.

The reactions are done in test tubes, starting The reactions are done in test tubes, starting with primers.with primers.

• PrimersPrimers are man-made, short nucleotide sequences are man-made, short nucleotide sequences that will base pair with sequences of DNA that are to that will base pair with sequences of DNA that are to be amplified.be amplified.

• A heat stable DNA polymerase is also needed.A heat stable DNA polymerase is also needed.


Tools for Tools for “Engineering” Genes “Engineering” Genes

The steps are relatively simple:The steps are relatively simple:• Researchers mix primers, polymerase, DNA of Researchers mix primers, polymerase, DNA of

choice, and nucleotides.choice, and nucleotides.• The mixture is exposed to precise temperature cycles The mixture is exposed to precise temperature cycles

in a dedicated machine.in a dedicated machine.• Starting with tiny quantities of DNA, the procedure Starting with tiny quantities of DNA, the procedure

doubles the DNA molecules in each round.doubles the DNA molecules in each round.

© 2007 Thomson Higher Education Fig. 22.15, p.417

a. PCR starts with afragment of double-stranded DNA

b. The DNA is heated to 90º-94ºC to unwind it. The singlestrands will be templates.

c. Primers designed to base-pair with ends of the DNAstrands will be mixed withthe DNA.

d. The mixture is cooled. Thelower temperature promotesBase pairing between theprimers and the ends of theDNA strands.

e. DNA polymerases recognizethe primers as start tags. Theyassemble complimentarysequences on the strands.This doubles the number ofidentical DNA fragments.


f. The mixture is heated again. The higher temperature make all of the double-stranded DNA fragments unwind.

Fig. 22.15, p.417

g. The mixture is cooled. The lower temperature promotesBase pairing between more primers added to the mixture and the single strands

h. DNA polymerase action again doubles the number of identical DNA fragments.

Section 7Section 7

““Sequencing” DNASequencing” DNA

““Sequencing” DNA Sequencing” DNA

Automated DNA sequencingAutomated DNA sequencing can reveal can reveal the sequence of nucleotides in DNA in a the sequence of nucleotides in DNA in a few hours.few hours.

The machines are loaded with four standard The machines are loaded with four standard nucleotides (A, T, G, and C) and four modified nucleotides (A, T, G, and C) and four modified versions of the nucleotides, which fluoresce a versions of the nucleotides, which fluoresce a different color.different color.

The DNA molecule to be sequenced, primer, The DNA molecule to be sequenced, primer, and polymerase are also added.and polymerase are also added.


A series of segments tagged with A series of segments tagged with fluorescing molecules are separated into fluorescing molecules are separated into sets of fragments, which are analyzed by sets of fragments, which are analyzed by the machine to reveal the original DNA’s the machine to reveal the original DNA’s nucleotide sequence.nucleotide sequence.


printout of DNA sequence:

TT CC CC AA AA AACCCCGG GGTT


To identify a particular gene among many in To identify a particular gene among many in a a gene librarygene library (say, inside bacteria), (say, inside bacteria), researchers use a radioactive probe that researchers use a radioactive probe that will match up with the DNA nucleotide will match up with the DNA nucleotide sequence of interest.sequence of interest.

Section 8Section 8

Mapping the Mapping the Human GenomeHuman Genome

Mapping the Human Genome Mapping the Human Genome

Results of the Results of the Human Genome ProjectHuman Genome Project indicate that the human genome is indicate that the human genome is composed of roughly 2.9 billion nucleotide composed of roughly 2.9 billion nucleotide bases subdivided into about 21,500 genes.bases subdivided into about 21,500 genes.



Genome mapping provides basic biological Genome mapping provides basic biological information.information.

Exons comprise only 1.5% of our DNA; the Exons comprise only 1.5% of our DNA; the remainder is non-coding DNA but should not be remainder is non-coding DNA but should not be labeled “junk.”labeled “junk.”

Our DNA is sprinkled with Our DNA is sprinkled with SNPsSNPs ( (ssingle ingle nnucleotide ucleotide ppolymorphisms), each of which has olymorphisms), each of which has a change in one nucleotide in sequence; these a change in one nucleotide in sequence; these account for the slightly different versions of the account for the slightly different versions of the genes that make us all different.genes that make us all different.


DNA chipsDNA chips help identify help identify mutations and diagnose diseases.mutations and diagnose diseases.

Each chip is a microarray of thousands of DNA Each chip is a microarray of thousands of DNA sequences stamped onto a small glass plate.sequences stamped onto a small glass plate.

• When a sample of body tissue is placed on the plate, When a sample of body tissue is placed on the plate, the reactions can pinpoint which genes are silent and the reactions can pinpoint which genes are silent and which are being expressed.which are being expressed.

• Some chips are being used to design better drug Some chips are being used to design better drug therapies for disease.therapies for disease.

As new genes are identified, it may be possible As new genes are identified, it may be possible to derive a complete genetic profile from a small to derive a complete genetic profile from a small sample of a person’s blood. sample of a person’s blood.

Figure 22.18aFigure 22.18a


Chromosome mapping shows where genes Chromosome mapping shows where genes are located.are located.

Sequencing of the genome can identify where Sequencing of the genome can identify where specific genes are located on chromosomes.specific genes are located on chromosomes.

• We know that chromosome 21 carries genes for We know that chromosome 21 carries genes for early-onset Alzheimer’s, epilepsy, and early-onset Alzheimer’s, epilepsy, and amyotrophic amyotrophic

lateral sclerosislateral sclerosis (ALS). (ALS).• More than 60 disorders have been mapped to More than 60 disorders have been mapped to

chromosome 14.chromosome 14.

Amyloidosis, cerebroarterial, Dutch-typeAlzheimer’s disease, one formSchizophrenia, chronic, one form

Amyotrophic lateral sclerosis, one form

Down syndrome (critical region)

Epilepsy, progressive myoclonusHemolytic anemia due to

phosphofructokinase deficiency

Homocystinuria, B6 responsive andB6 unresponsive

Leukemia, acute myeloidLeukocyte adhesion deficiency

12

11

2122

1

2

P

q

Fig 22.19, p.419


But there may be a down side to all of this But there may be a down side to all of this progress if genetic profiling leads to progress if genetic profiling leads to discrimination in employment or insurance discrimination in employment or insurance coverage.coverage.

Figure 22.18bFigure 22.18b

Section 9Section 9

Some Applications Some Applications of Biotechnologyof Biotechnology

Some Applications of BiotechnologySome Applications of Biotechnology

Researchers are exploring gene therapy.Researchers are exploring gene therapy. There are 15,500 known genetic disorders in There are 15,500 known genetic disorders in

humans.humans. Gene therapyGene therapy attempts to replace mutated attempts to replace mutated

genes with normal ones, or to insert genes that genes with normal ones, or to insert genes that restore normal controls over gene activity.restore normal controls over gene activity.

Genes can be inserted two ways.Genes can be inserted two ways. TransformationTransformation involves exposing cells involves exposing cells

cultured in the laboratory to DNA that contains cultured in the laboratory to DNA that contains the gene of interest; some small portion of the the gene of interest; some small portion of the DNA will be taken up by the cells and integrated DNA will be taken up by the cells and integrated into the host’s genome.into the host’s genome.


In In transfectiontransfection, DNA segments are inserted , DNA segments are inserted into viruses (often retroviruses) and then the into viruses (often retroviruses) and then the modified viruses are allowed to infect the target modified viruses are allowed to infect the target host cell; infection generally leads to insertion of host cell; infection generally leads to insertion of the DNA into the host genome.the DNA into the host genome.


Normal gene

Inject cellsinto patient

Clone normalgene intoretrovirus vector

Infect patient’swhite blood cells with virus

In some cells viral DNAInserts into chromosome

Fig 22.20, p.420


Results of gene therapy have been mixed. Results of gene therapy have been mixed. Severe combined immune Severe combined immune

deficiencydeficiency ( (SCID-X1SCID-X1) was one of the ) was one of the first successfully treated diseases first successfully treated diseases using gene therapy; however, several using gene therapy; however, several of the initial children treated for the of the initial children treated for the disease went on to develop cancer.disease went on to develop cancer.

Cystic fibrosis therapy trials have attempted to Cystic fibrosis therapy trials have attempted to deliver the corrective gene into the body using deliver the corrective gene into the body using a viral vector in a nasal spray; results have a viral vector in a nasal spray; results have been disappointing.been disappointing.



One of the most successful gene therapy One of the most successful gene therapy efforts is the treatment of some cancers such efforts is the treatment of some cancers such as malignant melanoma, leukemia, and lung as malignant melanoma, leukemia, and lung cancer.cancer.

• Viruses have been used to introduce interleukin Viruses have been used to introduce interleukin encoding genes to tumor cells; the interleukins serve encoding genes to tumor cells; the interleukins serve as a “suicide tag,” encouraging destruction of the as a “suicide tag,” encouraging destruction of the tumor by T cells.tumor by T cells.

• ““Lipoplexes” composed of plasmid wrapped in lipid Lipoplexes” composed of plasmid wrapped in lipid have also been used to deliver markers to tumors to have also been used to deliver markers to tumors to stimulate T cell destruction.stimulate T cell destruction.


Genetic analysis also is used to read DNA Genetic analysis also is used to read DNA fingerprints.fingerprints.

Each of us has a unique set of DNA fragments Each of us has a unique set of DNA fragments inherited from our parents in a Mendelian inherited from our parents in a Mendelian pattern—a pattern—a DNA fingerprintDNA fingerprint..

• Fingerprints form from short repeated segments Fingerprints form from short repeated segments called called tandem repeatstandem repeats..

• Tandem repeats can be separated and visualized by Tandem repeats can be separated and visualized by gel electrophoresisgel electrophoresis..


Variation can also be detected using Variation can also be detected using restriction fragment length polymorphismsrestriction fragment length polymorphisms ((RFLPsRFLPs); in RFLP analysis, DNA is cut into ); in RFLP analysis, DNA is cut into fragments using restriction enzymes and then fragments using restriction enzymes and then separated by electrophoresis.separated by electrophoresis.


Section 10Section 10

Issues for a Issues for a Biotechnological SocietyBiotechnological Society

Issues for a Biotechnological Society Issues for a Biotechnological Society

Some important concerns brought up for Some important concerns brought up for discussion in recent years include:discussion in recent years include:

The possibility that transgenic bacteria or The possibility that transgenic bacteria or viruses could mutate, possibly becoming new viruses could mutate, possibly becoming new pathogens.pathogens.

Bioengineered plants could escape from test Bioengineered plants could escape from test plots and become “superweeds” resistant to plots and become “superweeds” resistant to herbicidal control measures.herbicidal control measures.

Crop plants with added insect resistance could Crop plants with added insect resistance could bring forth new, even more formidable, insect bring forth new, even more formidable, insect pests.pests.


Transgenic species, such as fish, could feed Transgenic species, such as fish, could feed voraciously and displace natural species.voraciously and displace natural species.

Genetically modified plants, especially Genetically modified plants, especially those used for food, are particularly those used for food, are particularly controversial.controversial.

Critics allege that these Critics allege that these

““Frankenfoods” may be Frankenfoods” may be

toxic, less nutritious, and toxic, less nutritious, and

could promote antibiotic could promote antibiotic

resistance.resistance.Figure 22.23Figure 22.23


On the other hand, advocates for such foods On the other hand, advocates for such foods envision a envision a Green RevolutionGreen Revolution where these where these plants may help feed the world’s hungry people plants may help feed the world’s hungry people or be used to clean up pollution in a process or be used to clean up pollution in a process called called bioremediationbioremediation..

Figures 22.23 and 22.24Figures 22.23 and 22.24

Section 11Section 11

Engineering Bacteria, Engineering Bacteria, Animals, and PlantsAnimals, and Plants

Engineering Bacteria, Animals, and Plants Engineering Bacteria, Animals, and Plants

Bacteria were the first bioengineered Bacteria were the first bioengineered organisms; today they help produce many organisms; today they help produce many important human medicines such as human important human medicines such as human growth hormone, insulin, and interferons.growth hormone, insulin, and interferons.

Animals have been used in bioengineering Animals have been used in bioengineering experiments, and transgenic barnyard experiments, and transgenic barnyard animals may become the sources for animals may become the sources for pharmaceuticals: the blood clot dissolver pharmaceuticals: the blood clot dissolver tPA, CFTR protein for cystic fibrosis, and tPA, CFTR protein for cystic fibrosis, and blood-clotting factor VIII.blood-clotting factor VIII.


Animals have been used in bioengineering Animals have been used in bioengineering experiments, and transgenic barnyard experiments, and transgenic barnyard animals may become the sources for animals may become the sources for pharmaceuticals: the blood clot dissolver pharmaceuticals: the blood clot dissolver tPA, CFTR protein for cystic fibrosis, and tPA, CFTR protein for cystic fibrosis, and blood-clotting factor VIII.blood-clotting factor VIII.

Figures 22.23a and 22.27Figures 22.23a and 22.27


Plants can be conferred with desirable traits Plants can be conferred with desirable traits in the laboratory, such as resistance to in the laboratory, such as resistance to pathogens or herbicides, and then grown in pathogens or herbicides, and then grown in the field.the field.

Figure 22.25b-cFigure 22.25b-c

powerlecture: chapter 22 dna, genes, and biotechnology

Documents

structure of dna

behavior of dna

singlering structure

double helix slide

biotechnology slide

recombinant dna molecules

ribosomes ricin

impactsissues ricin