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Unit 4 - Molecular Genetics

Unit 4 - Molecular Genetics. DNA Replication Protein Synthesis Transcription Translation Cell Cycle. 1928 – Griffith. 1944 – Avery, McCarty, & McCleod. Bacteriophage. Viruses that attack bacterial cells (“bacteria eaters”). 1952 – Harvey & Chase. 1953  Watson & Crick (and Franklin).

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Unit 4 - Molecular Genetics

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  1. Unit 4 - Molecular Genetics • DNA Replication • Protein Synthesis • Transcription • Translation • Cell Cycle

  2. 1928 – Griffith

  3. 1944 – Avery, McCarty, & McCleod

  4. Bacteriophage • Viruses that attack bacterial cells (“bacteria eaters”)

  5. 1952 – Harvey & Chase

  6. 1953  Watson & Crick (and Franklin)

  7. 1958 – Meselson & Stahl

  8. DNA Structure • Nucleotides – the building blocks of DNA (nucleic acids)

  9. Base Pairing • A-T (double) • G-C (triple)

  10. 3’ vs. 5’ ends of DNA

  11. Gene – a portion of DNA that codes for a specific protein

  12. DNA Function • Transmission of genetic material to offspring • Basis of all cell processes (DNA RNA Protein) • Structure relates to function! • DNA structure provides a perfect template for semi-conservative replication

  13. Leading vs. Lagging Strands • Nucleotides can only be added to the 3’ end of a DNA molecule • THUS - DNA elongates only in the 5’  3’ direction

  14. DNA Replication • Starts at an origin of replication (ori) • Bacterial DNA is circular (only 1 ori) • Eukaryotic DNA is linear (multiple ori’s)

  15. 2. RNA primase(enzyme) recognizes an ori site on DNA, “sits” down on DNA, and synthesizes an RNA strand (5-10 nucleotides long) called a primer 3. DNA polymerase (enzyme) finds this primer and begins replication • Adds nucleotides in a 5’  3’ direction only!

  16. Replication fork – spots where DNA double strand “forks” • DNA helicase (enzyme) – unzips the DNA double helix

  17. 3a – Leading Strand • As the helix is unzipped, the 3’ end of leading strand is synthesized continuously • Only 1 RNA primer and 1 DNA polymerase is needed!

  18. 3b – Lagging Strand • Lagging strand is synthesized BACKWARDS in short chunks called Okazaki fragmentswith each getting: • RNA primer (thus RNA primase) • DNA polymerase (to synthesize DNA) • DNA ligase – enzyme that ligates (“sticks together”) Okazaki fragments together to form a single DNA strand

  19. DNA Replication Video • http://www.youtube.com/watch?v=teV62zrm2

  20. A few essential ideas to remember: • DNA copies itself almost always without error.(Approximately 1 true error per 10 billion bp; actually 1 error in 10,000 bp but DNA polymerases proof-read and fix) • Eukaryotic DNA replicates @ 50 nucleotides/second; bacterial DNA replicates much faster (10x)

  21. Proof-reading & Repair • DNA polymerases proof-read each strand against the parent template. • If error goes unrepaired by DNA polymerases, then other repair mechanisms kick in. • There are 130 different DNA repair enzymes in humans!

  22. An example…

  23. Telomeres • Telomere- a 100 to 1000 base-pair section at the tips of Eukaryote’s chromosomes (DNA) • Repeating sequences of TTAGGG (humans) • Function to protect the end of genes from being shortened by successive rounds of replication but telomeres themselves are shortened after each round of replication

  24. Telomeres can only be shortened so much (thus a cell can divide only so many times) and then the cell diesvia apoptosis (programmed cell death) • Get this: • Certain cells (e.g. germ cells) have telomerase, an enzyme that catalyzes the repair of telomere DNA damaged after replication • Certain types of cancer cells overexpress telomerasewhich allows those cells to continuously divide w/o consequence

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