Genetic Tranmission

Warm up

Group 1 – Griffith experiment (279) Group 2 – Avery experiment (279) Group 3 – Hershey-Chase (279-280) Group 4 – Watson-Crick and Franklin (281-

283) Group 5 – Meselson-Stahl experiment (284-

285) Write out a brief summary and state the

significance of the experiment(s) on the transparency

DNA structure Antiparallel

DNA replication

Origin of replication

Bacteria chromosomes 1 replication origin Recognized by a specific sequence

Eukaryotic chromosomes Hundreds or thousands of replication origin Multiple Replication “bubbles” occur

simultaneously

Elongation

Elongation

ss binding proteins hold strands apart Primase joins RNA nucleotides to template (primer) DNA polymerase III joins DNA nucleotides to template DNA polymerase I replaces primer

with DNA nucleotides

Elongation (more nuances)

Nucleoside triphosphate links to backbone, losing 2 phosphates (ENERGY!)

Lagging strand – Proceeds away from the replication fork Requires new primer for every okazaki

fragment (100 – 200 nucleotides) Fragments joined by ligase

DNA replication - summary

DNA replication summary

What is a gene? Beadle and Tatum

What is a gene? A DNA segment has information for

making the protein hemoglobin, which carries oxygen in your red blood cells

One allele will give information for producing normal hemoglobin

-Another allele (ONLY 1 base different) produces hemoglobin with 1 different amino acid

This difference makes the hemoglobin less soluble

When Oxygen levels are low, the hemoglobin molecules start sticking together, resulting in the red blood cell’s “sickle-shape”

Having both defective alleles will lead to multiple effects shown to the right

What is a gene?

Having only 1 defective allele (heterozygous) will not be fatal and actually beneficial!

Malaria is a disease spread by mosquitois that infects red blood cells

Being heterozygous results in your body destroying the red blood cells as well as the Malaria, leaving enough of the normal blood cells.

What is a gene?

Mendelian definition: Morgan definition: 1 gene-1polypeptide definition: What about noncoding region, non

translated RNA? “Region of DNA whose final product is

either a polypeptide or an RNA molecule” What do you think?

Genetic code

Genetic code

Transcription

1. Transcription initiation

Prokaryotes - RNA polymerase attaches to the promoter (startpoint and upstream nucleotides)

Eukaryotes – Transcription factors bind to TATA box region of promoter RNA polymerase II binds to promoter (transcription initiation complex)

Transcription elongation and termination 2. RNA polymerase

untwists DNA and joins RNA nucleotides (DNA rejoins as RNA strand peels away)

3. Prokaryotes – termination at a DNA certain DNA sequence

Eukaryotes – RNA polymerase goes beyond termination sequence (AAUAAA – polyadenylation)

Eukaryotic RNA modification 5’ end – modified GTP (protect from

degradation and is signal for ribosomes) 3’ end – poly(A) tail (same functions and

facilitates export from the nucleus) RNA

splicing

Post transcriptional nuances

Some organism’s intron RNA catalyzes splicing (ribozymes)

Introns may perform regulatory roles

Domains

tRNA structure and function

There are 61 codon combinations, but only 45 different tRNAs. Why?

Wobble position (A or G )

Connecting a.a. to the correct tRNA

Ribosome structure and function

Translation - initiation mRNA, tRNA, ribosomal subunits

brought together with help of initiation factors

1. Small ribosomal subunit binds to mRNA and initiator tRNA

2. Large ribosomal subunit attaches

Translation - elongation

Translation - termination

Translation nuances Polyribosomes Posttranslational modifications –

chemical modifications, removal of amino acids, polypeptide cleaved, joining of 2 polypeptides (hemoglobin)

DNA repair

Replication problems? Initial paring errors: 1/10,000 bases However, completed DNA has only 1 error

in every 1,000,000,000 bases DNA polymerase can’t add to the 5’ end of

daughter DNA strands (why don’t prokayrotes have this problem?)

DNA repair – solutions!

Mismatch repair: DNA polymerase proofreads nucleotides as it is added and corrects it immediately

Additional proteins perform mismatch repair

Excision repair (already damaged DNA) – nuclease removes DNA segment and DNA polymerase and ligase fill in with correct nucleotides

DNA repair – solutions!

Telomeres (non coding repeated sequence – TTAGGG)

Telomerase lengthens telomeres by incorporating its own RNA as template for new segment

Not found in most cells – only germ line cells and cancerous cells

Mutations Make a mini concept map using MOST or ALL

of the following terms (feel free to add more) : mutations, point mutations, substitutions, insertions, deletions, frameshift mutation, mutagens, missense mutations, nonsense mutations, wild type, codon, polypeptide, DNA replication, recombination, DNA repair, nondisjunction, aneuploidy, polyploidy, duplication, inversion, translocation, deletion