Genetic Tranmission

Warm up Group 1 – Griffith experiment (279) Group 2 – Avery experiment (279) Group 3 – Hershey-Chase ( ) Group 4 – Watson-Crick and Franklin ( ) Group 5 – Meselson-Stahl experiment ( ) 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

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

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