Chapter 10Nucleic Acids

& Protein Synthesis

DNA FANTASTIC

• After completing the chapter on Genetics, we discussed the passing on of genes, but how are genes produced?

Brief history of DNA Frederick GriffithFrederick Griffith – 1928 • Experimented with pneumonia bacteria. Grew 2 strains of

bacteria

– 1 formed smooth colonies and causing pneumonia– The other forms rough colonies and is harmless. Heat kills disease causing strain - mice don’t get pneumonia.Injects rough, harmless strain into mice, mice are fine. Adds heat killed harmful strain to the harmless strain injected into

mice. The mice die.

He cultures the bacteria. Finds that the harmless rough bacteria had been “transformed” or changed into the lethal strain.

Griffith’s Transformation Experiment

• The harmless bacteria were transformedtransformed by some factor from the harmful bacteria

• Did not know what that factor was though

Conclusion

Oswald Avery and company 1944• Repeated Griffith’s work but used enzymes

(lipases, proteases and carboases) to destroy proteins, lipids and carbs in the heat killed bacteria.

• Pneumonia and transformation still occurred. • Then used an enzyme to destroy RNA. Still

transformed. • Finally, used an enzyme to break apart DNA. • This stopped transformation

Conclusion• DNA is the nucleic acid that stores and

transmits genetic information.

Hershey and Chase – 1952• Used T4 bacteriophage virus that infects E.

coli bacteria to study viral inheritance• A virus is a non-living pathogenic particle

that can’t replicate on its own

Capsid (protein)

The Lytic Cycle of Virus infection

Attaches onto host cell Injects DNA into host cell Replication of Viral parts

Reassembly of virons Lysis – bursting out

What part of a virus actually infects & causes the host cell to become a viral factory?

Used radioactive isotopes of P31 and S32. P32 and S35

Proteins may contain sulfur but do not have Phosphorus

DNA is made up of Phosphate groups but doesn’t contain Sulfur

Used S35

Used P32

Found that the S35 stayed outside the cell & P32 ended up in new vironsAnimation

Conclusion

The genetic material of the bacteriophage is located in the DNA,

not the protein coat

Erwin Chargaff – 1940’s

Noticed a pattern in the amounts of the four bases: Adenine, Guanine, Cytosine, and Thymine

• Found the number of Guanine & Cytosine nitrogen bases is always equal in DNA

• & the number of Thymine and Adenine is always equal.

• Didn’t know why though!

History of DNAHistory of DNA:• Rosalind FranklinRosalind Franklin took X-Ray diffraction

photo (Photo 51) of DNA. – Determined that DNA was a double helix with the

bases in the center.

Watson and CrickWatson and Crick (1953) • Using Franklin’s Photo

51, came up with the double helix form of double helix form of DNA. Won Nobel Price w/ Maurice Wilkins (1962).

Original DNA model.

Structure of DNAStructure of DNADeoxyribonucleic acid

Polymer of the monomer – Nucleotides

Single nucleotide

5 carbon sugar –Deoxyribose

A phosphate group

A nitrogen baseS

P

N-base

Nucleotide Sugar & phosphate alternate to make up the sides of the strand

Found only in nucleus

4 nitrogen bases •Guanine - Purine

•Cytosine - Pyrimidine

•Adenine - Purine

•Thymine - PyrimidineFollow base pairing rule

Adenine with Thymine Guanine with CytosineBases are held together by weak hydrogen bonds

N-bases connect to sugars by a covalent bond

5 Carbon sugar

Phosphate group

Nitrogen base

Weak H bond

Covalent bond

In Cell Reproduction, we keep mentioning DNA replication. How does DNA do this?

• Occurs during Interphase – Makes 2 exact copies of the original. If not, a mutation occurs.1. The double helix unwinds and flattens out (like a zipper)2. An enzyme DNA helicase (like the zipper slide) unzips the

strand at the weak hydrogen bonds. This exposes the Nitrogen bases (each tooth of the zipper)

3. Another enzyme, DNA polymerase will be responsible for rezipping the strands. It will take free nucleotides in the nucleus and bond them to the exposed bases, following the base pair ruling – G – C and A – T.

4. The base pairing continues until the entire strand has their complement.

5. Now there are two identical strands of DNAAnimation

DNA helicase unzips

Original (old) strands of DNA are on the outside of the new strands.

Replicates from the center with aid of DNA polymerase

Semi-conservative model

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GLENN!!!

So if DNA reads the following: _- G C – G C – __ _ - G A - _ A – T A – __ _ - T T - _ T – A T – __ _ - A C - _ C – G C – __ _ - G _ - C G - G G – __ _ - G _ – T A - T A – __ _ - T

T - _ T A T – __ _ - A C - _ C - G C – G C – __ _ - G _ - T __ - T A - __ A – __ _ - T _ - A T - __ __ - A T – __ _ - A _ - G __ – G C – __ C – __ _ - G _ - C G – __ __ – C G – __ _ – C Original strand Replication process Replicated strands

cc

Here is a song

How good at replicating is DNA?

• Accurate to about 1 error for every 10,000 base pairs. With DNA “ proof-reading” and repair, brings # of errors to only 1/1 1/1 billionbillion

• Rate of 40 bases per second!!!!Rate of 40 bases per second!!!!

• Gene Mutation – error resulting from misread of DNA or problem in the translation process later on. (We’ll come back to this later)

RNA Ribonucleic acidRibonucleic acid

The other Nucleic Acid

• Acts as a messenger between DNA and the ribosomes and carries out protein synthesis

• DNA is too large to get out of the nucleus. Uses RNA to bring its message to the rest of the cell for protein synthesis

How DNA & RNA DifferRNA is single stranded helix

Has Ribose sugar instead of Deoxyribose

Contains Uracil in place of Thymine so Adenine

bonds with Uracil

Can be found in the nucleus, cytoplasm or at the ribosomes

Three different kinds of RNA

• Messenger RNA (mRNA)Formed in the nucleus & goes to the

ribosomes. Carries genetic code from DNA, through the cytoplasm to the ribosomes

• Transfer RNA (tRNA) – t-shaped. Carries amino acids to the mRNA in the ribosomes.

• Ribosomal RNA (rRNA)Most abundant. RNA in globular form.Makes up the ribosomes

Messenger RNA (mRNA)•Since DNA is too large to leave the nucleus, it must use mRNA to get

it’s message out

•mRNA nucleotides are free in the nucleoplasm

•RNA polymerase allows for mRNA synthesis to compliment DNA

•If DNA is: CTA CGG AGA,

• mRNA is: GAU GCC UCU (Remember, U substitutes for T in RNA)

•This is called Transcription.

Transfer RNA (tRNA) • Are free in cytoplasm • Go to the ribosomes to get DNA’s

message from the mRNA • Transfer amino acids from the cytoplasm

to the ribosomes

Ribosomal RNA (rRNA)

• Found only making up the ribosomes. • Responsible for overseeing that the

process of Protein synthesis occurs properly.

Now for DNA’s real jobNow for DNA’s real job.DNA rap

• Protein synthesisProtein synthesis – Process by which DNA codes for the

production of proteins (polypeptide chains) & protein assemblyPolypeptide chains are polymers of the 20 different amino acids.

Genetic code – Coded for on the DNA that translates into the production of a polypeptide chain made up of amino acids

Transcription

Translation

Polypeptide formingAmino Acid

1. Process begins in the nucleus w/ the Transcription of DNA by mRNA

– DNA flattens and is unzipped exposing its bases (template)

– RNA polymerase binds free RNA nucleotides to exposed DNA bases starting at a promoter – TAC (like a capital letter at start of a sentence).

– Base rule pattern is the same as in replication w/ the exception of Thymine. THERE IS NO THYMINE IN RNA. Instead, Adenine bonds with Uracil and Thymine from DNA would bond with Adenine.

– Transcription continues until a termination signal is given (like a period) to stop the transcription process

• If DNA reads: ATC GTC GAT TGG C AA• mRNA: UAG CAG CUA ACC GUU• mRNA leaves the nucleus through a pore to go

out into the cytosol to a ribosome

• At the ribosome, the process of Translation occurs.

• mRNA will temporarily bind with the ribosome

• Starting with the start codon (AUG), in groups of 3, mRNA will determine which Amino acid tRNA must bring to the ribosome.

• Animation – Virtual Cell

TranscriptionTranscription

TranslationTranslation

Polypeptide formingPolypeptide forming

Central Dogma Song Sing along - YouTube

• Codons are groups of 3 adjacent bases on mRNA (AAA, CCC GGG)

• Each codon will specify a specific Amino Acid. This is called Translation. 64 different codons

• Free floating amino acids in the cytosol are transported to mRNA by tRNA.

• tRNA attaches to mRNA by the anticodon• If DNA reads:A T G G T C G A T T G G CAA• mRNA: U A C C A G C U A A CC GUU• tRNA: A U G G U C G A U U GG

CAA• Translation:• Amino Acid: Tyrosine - Glutamine – Leucine -Threonine - Valine

Start codon

Stop Codons

DNA mRNA Protein

Transcription Translation

Protein Synthesis

• Once tRNA brings the correct amino acid to mRNA at the ribosome, it releases to go & get more amino acids.

• Adjacent amino acids bond together at a peptide bond peptide bond to form a polypeptide.

• Chain could be up to 10,000 amino acids long

• tRNA with the anticodon (complimentary to mRNA) links to mRNA. It carries a specific Amino Acid (specified by mRNA).

• When adjacent Amino Acids link together, they form a peptide bond.

• The first tRNA releases, then the next codon goes into place and another Amino Acid is brought in by a tRNA. This continues until the entire message is translated.

• The chain of Amino Acids is formed called a Polypeptide (protein). The translation ends when a STOP codon is reached (UAA, UAG, UGA).

• DNA codes for mRNA, • mRNA carries the information

needed for the synthesis of coded proteins in the ribosomes.

• tRNA is the go-for that brings the amino acids to the ribosomes to make the protein).

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Protein Synthesis • Production of Proteins coded for by DNA• AnimationProtein Synthesis - Learning • You tube animation – really good!• McGraw animation• http://www.youtube.com/watch?

v=41_Ne5mS2ls – HHMI one• Replication & Protein synthesis – song with

only typed words but good• Central Dogma Song

• Does this process ever make a mistake?• Have you ever had to copy a large amount

of information? • What is the likelihood of you making a

mistake or more?• What could cause these changes?

Changes in genetic material

Gene Mutations: alters one or more genes

Chromosomal Mutations:alter the entire chromosome or a portion of it.

Gene Mutations

Point MutationsPoint Mutations – affect only one amino acid

Frameshift mutationsFrameshift mutations – May affect an entire amino acid sequence.

Point mutation

• involves a substitution in one or a few nucleotides.

• Usually influences a single amino acid in the polypeptide change. Caused by a substitution of a Nitrogen base.

• THE FAT CAT ATE THE RAT • Take out “C” in Cat & substitute a “B” • THE FAT BAT ATE THE RAT• Does not really change the meaning to

the sentence or the protein formed

• If DNA reads: A T G G T C G A T T G G CAA• mRNA: U A C C A G C U A AC C GUU• Amino Acid: Tyrosine - Glutamine – Leucine -Threonine – Valine

• But if mRNA: U A C C A G C A A AC C GUU• The AA: Tyrosine – Glutamine – Glutamine – Threonine – Valine

• This is an example of a missense point mutation

Substitutions – THE FAT CAT ATE THE RAT THE FAT BAT ATE THE RAT– Is the replacement of one nucleotide and its partner with another pair

of nucleotides– Can cause missense or nonsense

Figure 17.24

Wild typeA U G A A G U U U G G C U A AmRNA 5

Protein Met Lys Phe Gly Stop

Carboxyl endAmino end

3

A U G A A G U U U G G U U A A

Met Lys Phe Gly

Base-pair substitutionBase-pair substitutionSilent mutation: No effect on amino acid sequenceSilent mutation: No effect on amino acid sequence

U instead of C

Stop

A U G A A G U U U A G U U A A

Met Lys Phe Ser Stop

A U G U A G U U U G G C U A A

Met Stop

MissenseMissense A instead of G

NonsenseNonsenseU instead of A

Frameshift mutation

• involves a change in the entire protein formed or a large portion of it.

• Caused by insertions (additions) or deletions of Nitrogen bases.

• THE FAT CAT ATE THE RAT • Take out “E” in THE & group into

3’s • THF ATC ATA TET HER AT_

This makes no sense at all!!

• If DNA reads: A T G G T C G A T T G G CAA• mRNA: U A C C A G C U A AC C GUU• AA: Tyrosine - Glutamine – Leucine -Threonine – Valine• BUT if mRNA: U A C C A G U A A C C G U U _• THEN Amino Acid: Tyrosine - Glutamine – STOP!!!!

• The entire sentence makes no sense. The protein formed would be totally different

Insertions and Deletions– THE FAT CAT ATE THE RAT THE ATC ATA TET HER AT- – Are additions or losses of nucleotide pairs in a gene– May produce Frameshift mutationsFrameshift mutations

mRNAProtein

Wild type

A U G A A G U U U G G C U A A5

Met Lys Phe Gly

Amino end Carboxyl end

Stop

Base-pair insertion or deletionFrameshift causing immediate nonsenseFrameshift causing immediate nonsense

A U G U A A G U U U G G C U A

A U G A A G U U G G C U A A

A U G U U U G G C U A A

Met Stop

U

Met Lys Leu Ala

Met Phe Gly Stop

MissingA A G

Missing

Extra U

Frameshift causing Frameshift causing extensive missenseextensive missense

Insertion or deletion of 3 nucleotides:Insertion or deletion of 3 nucleotides:no frameshift but extra or missing amino acidno frameshift but extra or missing amino acid

3

So which form of a mutation would be more severe?

• Frameshift mutationFrameshift mutation … …since an entirely new protein could

be formed

CHROMOSOMAL MUTATIONS

• involve changes in number and structure of the chromosomes.

• Could change location of genes on the chromosomes or the number of copies of some of the genes.

• Deletions – part of a chromosome is missing

Duplications – Extra copies of genes are inserted

• Inversions – Reverse direction of parts of the chromosome

Chromosomal Mutations animation

Parts of one non-homologous chromosome breaks off and attached onto another non-homologous chromosome

Translocations

Females Males

Date Wild type

wings, wild type body

Wild type wings,

ebony body

Vestigial wings, wild type body

Vestigial wings,

ebony body

Wild type wings, wild type body

Wild type wings,

ebony body

Vestigial wings, wild type body

Vestigial wings,

ebony body

Your F2 Totals

Class Totals

Females Males

Date Wild type

wings, wild type body

Wild type wings,

ebony body

Vestigial wings, wild type body

Vestigial wings,

ebony body

Wild type wings, wild type body

Wild type wings,

ebony body

Vestigial wings, wild type body

Vestigial wings,

ebony body

Your F2 Totals

Class Totals