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Genetic Tranmission

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)

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Genetic Tranmission

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  1. Genetic Tranmission

  2. 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

  3. DNA structure • Antiparallel

  4. DNA replication

  5. 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

  6. Elongation

  7. 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

  8. 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

  9. DNA replication - summary

  10. DNA replication summary

  11. What is a gene? Beadle and Tatum

  12. 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

  13. 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.

  14. 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?

  15. Genetic code

  16. Genetic code

  17. Transcription

  18. 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)

  19. 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)

  20. 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

  21. Post transcriptional nuances • Some organism’s intron RNA catalyzes splicing (ribozymes) • Introns may perform regulatory roles • Domains

  22. tRNA structure and function • There are 61 codon combinations, but only 45 different tRNAs. Why? • Wobble position (A or G )

  23. Connecting a.a. to the correct tRNA

  24. Ribosome structure and function

  25. 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

  26. Translation - elongation

  27. Translation - termination

  28. Translation nuances • Polyribosomes • Posttranslational modifications – chemical modifications, removal of amino acids, polypeptide cleaved, joining of 2 polypeptides (hemoglobin)

  29. 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?)

  30. 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

  31. 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

  32. 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

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