biology 30

Students will explain classical genetics at the molecular level

• Summarize the historical discovery of the DNA molecular structure by Franklin, Watson and Crick

• Describe how genetic information is contained in the sequence of bases in DNA

• Describe DNA replication

Some History

• 1928– Frederick Griffith (British)– Studied Streptococcus Pneumoniae

• pneumonia bacteria• two genetic strains• Colonies appeared smooth (S type)

– Surrounded by a mucous coat or capsule• Colonies that appeared rough (R type)

• In 1928, Frederick Griffith performed an experiment using pneumonia bacteria and mice. This was one of the first experiments that hinted that DNA was the genetic code material.

• He used two strains of Streptococcus pneumoniae:– a “smooth” strain which has a polysaccharide coating

around it that makes it look smooth when viewed with a microscope,

– a “rough” strain which doesn’t have the coating, thus looks rough under the microscope.

– When he injected live S strain into mice, the mice contracted pneumonia and died.

– When he injected live R strain, a strain which typically does not cause illness, into mice, as predicted they did not get sick, but lived.

• Thinking that perhaps the polysaccharide coating on the bacteria somehow caused the illness and knowing that polysaccharides are not affected by heat, Griffith then used heat to kill some of the S strain bacteria and injected those dead bacteria into mice. – This failed to infect/kill the mice, indicating that the

polysaccharide coating was not what caused the disease, but rather, something within the living cell.

– Since Griffith had used heat to kill the bacteria and heat denatures protein, he next hypothesized that perhaps some protein within the living cells, that was denatured by the heat, caused the disease.

• He then injected another group of mice with a mixture of heat-killed S and live R, and the mice died! – When he did a necropsy on the dead mice, he

isolated live S strain bacteria from the corpses. • Griffith concluded that the live R strain

bacteria must have absorbed genetic material from the dead S strain bacteria, and since heat denatures protein, the protein in the bacterial chromosomes was not the genetic material.

• This evidence pointed to DNA as being the genetic material.

Functions of DNA

• Controls cellular activities of an organism by

1. Coding for structural proteins2. Coding for enzymes

Nucleic Acids• DNA

– Deoxyribonucleic Acid– Genetic material– Can self-replicate– Made up of Nucleotides

• Shape = double helix– A twisted rope ladder– A full twist every 10 nucleotides

DNA Discovery

• Rosalind Franklin was using X-Ray Diffraction to study DNA

• Her work allowed Watson and Crick to come up with model of DNA

• Findings presented in 1953• Visually confirmed in 1969

Nucleotides• Nucleotides are composed of

– A sugar• five carbons• Deoxyribose

– A phosphate• PO4-

– One of 4 nitrogen bases1. Adenine [A]2. Thymine [T]3. Cytosine [C]4. Guanine [G]

The sugar-phosphate

groups are the side rails of

ladder and the the nitrogen bases are the

rungs

Nucleotides• The two strands of DNA are complimentary

because the nitrogen bases bond with each other according to some rules.

1. Adenine will only bond with Thymine2. Guanine will only bond with Cytosine

• Nitrogen bases bond via hydrogen bonds.• These break over 70oC (denature)

http://207.207.4.198/pub/flash/24/menu.swf

http://207.207.4.198/pub/flash/24/menu.swf

DNA REPLICATION

• DNA must have the ability to create an exact duplicate of itself

• The sequence in one strand determines precisely what the sequence of nucleotides in the other strand will be. (A-T, G-C)

DNA REPLICATION1. The hydrogen bonds holding the two

complimentary strands together break2. DNA strands separate3. Free floating complimentary nucleotides

match up with nucleotides on the parent DNA strand.

– Catalyzed by DNA polymerase4. New, semi-conservative strands are

formed

DNA REPLICATION• Semi-conservative

– The daughter strands are made up of one half old strand on one half new strand

• The DNA unzips due to the hydrogen bonds between the bases being broken

• These exposed bases attract free floating bases, which are attached to the chain by DNA polymerase.


• Describe RNA transcription• Describe how genetic information is

translated into amino acid chains in proteins• Explain how mutations result in

abnormalities or create genetic variability• Explain how base sequences in nucleic

acids give evidence for evolution

DNA vs RNA

DNARNA

DNA vs RNA

DNA• Double stranded

RNA

DNA vs RNA

DNA• Double stranded

RNA• Single stranded

DNA vs RNA

DNA• Double stranded• Deoxyribose sugar

RNA• Single stranded

DNA vs RNA

DNA• Double stranded• Deoxyribose sugar

RNA• Single stranded• Ribose sugar

DNA vs RNA

DNA• Double stranded• Deoxyribose sugar• Nitrogen bases

– Cytosine


DNA vs RNA


– Cytosine – Guanine


DNA vs RNA


– Cytosine – Guanine– Adenine


DNA vs RNA


– Cytosine – Guanine– Adenine– Thymine


DNA vs RNA



RNA• Single stranded• Ribose sugar• Nitrogen bases

– Cytosine

DNA vs RNA




– Cytosine– Guanine

DNA vs RNA




– Cytosine– Guanine– Adenine

DNA vs RNA




– Cytosine– Guanine– Adenine – Uracil [U]

DNA vs RNA

DNA• One type of DNA

RNA

DNA vs RNA


RNA• Many types of RNA

DNA vs RNA



– Messenger RNA (mRNA)

DNA vs RNA



– Messenger RNA (mRNA)– Transfer RNA (tRNA)

DNA vs RNA



– Messenger RNA (mRNA)– Transfer RNA (tRNA)– Ribosomal RNA (rRNA)

DNA vs RNA



– Messenger RNA (mRNA)– Transfer RNA (tRNA)– Ribosomal RNA (rRNA)– Small nuclear RNA

(smRNA)

DNA vs RNA


• Mostly in nucleus



(smRNA)

DNA vs RNA


• Mostly in nucleus



(smRNA)• Mostly found in

cytoplasm

DNA vs RNA


• Mostly in nucleus• Can self-replicate

under the right conditions




cytoplasm

DNA vs RNA


• Mostly in nucleus• Can self-replicate

under the right conditions




cytoplasm• Cannot self-replicate

Genes and Proteins

• A gene is a segment of DNA–Carries the information of the

synthesis of a protein• One gene codes for one

protein

A Great Animation with notes!!

http://www.lewport.wnyric.org/jwanamaker/animations/Protein%20Synthesis%20-%20long.html

Proteins in the Body• Enzymes• Hormones • Antibodies • Hemoglobin• Cell membranes• Receptor molecules• Carrier molecules

Composition of Proteins• Made up of 20 different amino acids• Sequence of a.a.’s identifies protein• Sequence of bases in DNA determines Sequence of

a.a.’s • One gene = one protein• Protein Synthesis relies on 3 types of RNA

– rRNA–mRNA– tRNA

Types of RNA• Ribosomal RNA (rRNA)

– Makes up the ribosomes• Messenger RNA (mRNA)

– Involved in transcription (first stage of protein synthesis)– Carries message from DNA in nucleus to ribosome in

cytoplasm• Transfer RNA (tRNA)

– carries amino acids to mRNA All RNA produced in nucleolus.

tRNA & rRNA- In cytoplasm only

mRNAin cytoplasm & nucleus

Protein Synthesis • Occurs primarily in ribosomes• Instructions for protein contained in DNA• Message must get from nucleus to cytoplasm

(DNA to ribosome)• Process occurs in 2 steps

1. Transcription2. Translation

http://www.pbs.org/wgbh/aso/tryit/dna/

http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

Protein Synthesis Summary1. mRNA is made using DNA template2. mRNA exits nucleus3. tRNA picks up aa’s4. tRNA anticodon bonds to mRNA codon5. Peptide bond forms between aa’s 6. Protein used by cell or packaged & exported7. mRNA breaks into free nucleotides 8. tRNA’s free to pick up more aa’s

Transcription

Translation

Transcription• In nucleus• mRNA made using DNA as a template • If the DNA base sequence is A A T T C C G G A (3 triplets)• The mRNA molecule manufactured would be U U A A G G C C U (3 triplets)

• Each triplet is a codon

Code must be transcribed then translated

TranscriptionDNA used as template

to build mRNA

mRNAbuilt

using DNAas a

template

Codons• Code for amino acids• May code for start (initiator codon)• May code for stop (terminator codon)• AUG is an initiator codon but also codes for the

amino acid methioine• If code AUG is in middle it must code for

methionine

Data table of mRNA codonssupplied in diploma!!

Can be used to work out DNA, tRNA or

amino acid sequence

Translation• mRNA arrives at ribosome• tRNA molecules with a.a.’s are

attracted to this mRNA– complimentary rule (A attracts U

etc….)• 20 a.a.’s therefore

– 20 different tRNA’s

TranslationmRNA U U A A G G C C U

3 codons

TranslationmRNA U U A A G G C C U

tRNA A A U U C C G G A

3 anticodons

Transfer RNA

Translation Initiation

Identify codons and anticodons

Identify peptide bonds, ribosome & protein

Translation 1

Translation 2

Translation 3

Translation 4

Translation 5Name the products!

TranslationRequires many Ribosomes

The golgi apparatus will package the protein to be used for different functions throughout the

body.

http://www.eolas.ca/Micro_2.htm

http://www.westga.edu/~lkral/prtsynth/prtsynth.mov

Review Questions• mRNA codon for AAT DNA triplet =• DNA triplet for CCG mRNA codon =• tRNA anticodon for GCA DNA triplet =• mRNA codon for GAU tRNA =• tRNA anticodon for UUA mRNA codon =• DNA triplet for CUA anticodon =• codon for UAG anticodon =• anticodon for CTA DNA triplet =

Answers to Review Questions• mRNA codon for AAT DNA triplet = UUA• DNA triplet for CCG mRNA codon = GGC• tRNA anticodon for GCA DNA triplet = GCA• mRNA codon for GAU tRNA = CUA• tRNA anticodon for UUA mRNA codon = AAU• DNA triplet for CUA anticodon = CTA• codon for UAG anticodon = AUC• anticodon for CTA DNA triplet = CUA

Mutations• Changes in the sequence of bases in DNA• Caused by mutagenic substances like

– X-rays – cosmic rays– UV light– Some chemicals

• Mutagens can affect a single point in the DNA or it can affect large sections.

• Result = the proteins that the DNA codes for will be altered.

Mutations• 3 types of mutations.

1. INSERTION– An extra nucleotide is inserted into the DNA– Causes a frame shift

2. DELETION– A nucleotide is deleted from the DNA– Causes a frame shift

3. SUBSTITUTION– One nucleotide is substituted for another

Using DNA to explain Evolution

• Species that are closely related will share very similar DNA sequences

• Scientists use mitochondrial DNA (mtDNA) to study the relationship between species

• Used to explain variety of ethnic groups found throughout the world (all from African descendents)

Using SINEs and LINEs

• SINEs and LINEs are repeated DNA sequences that don’t code for anything, but show an evolutionary relationship

• Finding a SINE or LINE in two species and not in other species, signifies that the first two species must be more closely related to each other than to the other species


• Explain DNA transformation – (recombinant DNA)

• Describe the role of restriction enzymes and ligases in transformation

Genetic Engineering

• A desired gene can be isolated and millions of copies made

• These copies can then be analyzed to determine the gene’s nucleotide sequence

• This nucleotide sequence can be decoded to find the sequence of amino acids in the corresponding protein

Genetic Engineering• Functioning genes can be transferred into cells

or bacteria, yeasts, plants, animals– i.e. 1928 – Griffith

• DNA can be “made to order” using “gene machines” that can be programmed to produce short strands of DNA in any desired sequence– Useful for studying DNA, – protein synthesis experiments

• Change genetic code to eliminate particular amino acids from a protein

• Find how the amino acid affects the protein’s function

Transformation

• Transformation is the process whereby one strain of a bacterium absorbs genetic material from another strain of bacteria and “turns into” the type of bacterium whose genetic material it absorbed. Because DNA was so poorly understood, scientists remained skeptical up through the 1940s.

Genetic Engineering Recombinant DNA

• To recombine DNA–A technique to determine gene

expression–Gene segments from different

sources are recombined in vitro and transferred into cells (usually E. coli) to see what happens.



• First successful GE experiment with human DNA took place in 1980–Human gene which codes for the

protein interferon was successfully introduced into a bacteria cell…• The bacteria produced human protein.

–Interferon combats viral infections and may help in fighting cancer



1. The desired gene is isolated and cut out of the DNA

• A “restriction enzyme” (restriction endonuclease) does this

2. Isolated gene is inserted into a bacterial plasmid using a ligase

• Ligase is an enzyme which normally repairs breaks in the DNA backbone

• New DNA now called recombinant DNA

Genetic Engineering Recombinant DNA – How It Works


3. The plasmid is absorbed by a bacterium• Reproduces asexually to produce many

clones containing the recombinant DNA

4. Bacterial cells produce the protein coded by the foreign gene

• Desired protein can be isolated and purified from the culture.



• Examples of recombinant DNA technology…

• Interferon• Human growth hormone• Human insulin• Gene Therapy• Agriculture…


RestrictionEnzymes cut

Ligaseacts as glue rDNA

Recombinant DNA Technology

Sticky end

Restriction Enzyme

Gene insertion


• Gene Therapy– Replacement of defective genes with normal

healthy genes• e.g. Cystic fibrosis, hemophilia, sickle-cell anemia,

immune-deficiencies• OBSTACLES today include …

– How to fit genes into the body cells– How to control the introduced genes



• Agriculture– Introduction of genes for resistance to

disease, drought, frost, increased protein production, larger fruit…

• Used in forensic studies…• Small quantities of blood, semen, or other tissue

can be tested for the DNA base sequence• The DNA nucleotide sequence is unique for every

individual (except identical twins)• A technology called RFLP auto-radiography is used

to display selected DNA fragments as bands

Genetic Engineering DNA Fingerprinting

• Radioactive probes mark the bands that contain certain markers…

– Only 5 or 10 regions of the entire genetic content of the cell are tested• This was a defense argument used by the O.J.

Simpson lawyers

• The probability of having matching DNA fingerprints is about 1 in a million.

Genetic Engineering DNA Fingerprinting

biology 30

Documents

live r dna of s

live r strain bacteria

live s strain bacteria

live r r bacterias bacteriain

dead s strain bacteria

dead bacteria

dead mice

smooth s typesurrounded