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Molecular Basis of Inheritance

Molecular Basis of Inheritance. AP Biology Crosby High School. Frederick Griffith (1928). Streptococcus pneumoniae Lethal smooth strain vs. Harmless rough. Hershey – Chase Experiment. T2 reprogrammed E. coli Alfred Hershey and Martha Chase (1952). Additional Support for DNA.

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Molecular Basis of Inheritance

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  1. Molecular Basis of Inheritance AP Biology Crosby High School

  2. Frederick Griffith (1928) • Streptococcus pneumoniae • Lethal smooth strain vs. Harmless rough

  3. Hershey – Chase Experiment • T2 reprogrammed E. coli • Alfred Hershey and Martha Chase (1952)

  4. Additional Support for DNA • Eu. Cells copy DNA exactly before Mitosis • Diploid cells exactly twice as much DNA as Haploid gametes • Chargaff’s rule • %A = %T • %G = %C

  5. The Players

  6. Watson and Crick • James Watson visited Maurice Wilkins at Cambridge • Noticed Rosalind Franklin’s X-ray image of DNA • Took it to Francis Crick who recognized a helix structure

  7. Double – Helix Calculations • Width of helix suggested two strands • One complete turn every 3.4 nm • Base pairs .34 nm apart • Purines must be paired specifically with Pyrimidines • Supported Chargaff’s rule

  8. The Structure

  9. DNA Replication • Proposed types • Conservative: Original DNA remains intact • Semi-conservative: Half original and half daughter • Dispersive: All four strands have old and new • 6 billion base pairs copied • Takes only a few hours • 1 mistake out of 1 billion nucleotides

  10. Proposed Replications

  11. Origin of Replication • Recognize specific portion to open molecule • Begins copying in both directions • Number of Origins • Prokaryotic: 1 origin of replication • Eukaryotic: May have hundreds or thousands • Replication fork • Y-shaped region of origin of replication

  12. Elongation of New DNA Strands • Catalyzed by DNA Polymerases • Bacteria: 500 nucleotides / sec • Humans: 50 nucleotides / sec • Energy supplied by nucleoside triphosphates • ATP, GTP, CTP, TTP • Nucleotide and phosphate join strand • Pyrophosphate releases energy through hydrolysis

  13. Elongation

  14. Antiparallel DNA Strands

  15. Leading and Lagging Strand • Only elongates in 5’  3’ Direction • Lagging strand contains Okazaki fragments (100-200) • DNA Ligase joins fragments

  16. Primase Begins Replication • Primase: joins RNA together to form a primer • DNA Polymerase adds to the primer • Another polymerase replaces the RNA primer with DNA • Leading strand needs only one primer • Lagging strand needs one primer for each Okazaki fragment

  17. DNA Proofreading • DNA polymerase checks for errors and corrects them as it elongates • Mismatch Repair: fixes incorrectly paired nucleotides • Nucleotide Excision Repair • Thymine – Thymine Dimers

  18. Excision Repair

  19. Telomeres • Exist at the ends of DNA • Multiple repetitions of TTAGGG • Between 100 – 1,000 repeats • Telomerase replaces telomeres in germ cells • If the repeats run out then the cells die

  20. Telomerase

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