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DNA Structure and Functions

DNA Structure and Functions. Outline. Genetic Material Transformation Viral Reproduction Bacteriophages Hershey and Chase DNA Structure Watson and Crick DNA Replication Prokaryotic versus Eukaryotic Replication Errors. Genetic Material.

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DNA Structure and Functions

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  1. DNA Structure and Functions Mader: Biology 8th Ed.

  2. Outline • Genetic Material • Transformation • Viral Reproduction • Bacteriophages • Hershey and Chase • DNA Structure • Watson and Crick • DNA Replication • Prokaryotic versus Eukaryotic • Replication Errors Mader: Biology 8th Ed.

  3. Genetic Material • In 1931, bacteriologist Frederick Griffith performed an experiment with the bacterium Streptococcus pneumoniae and concluded that virulence passed from the dead strain to the living strain. • Transformation • Further research by Oswald Avery and others discovered that DNA is the transforming substance. Mader: Biology 8th Ed.

  4. Griffith’s Transformation Experiment Mader: Biology 8th Ed.

  5. Reproduction of Viruses • Bacteriophages are viruses that infect bacteria. • Viruses consist of a protein coat (capsid) surrounding a nucleic acid core. • Phage DNA contains genetic information necessary to produce new phages. Mader: Biology 8th Ed.

  6. Bacteria and Bacteriophages Mader: Biology 8th Ed.

  7. Reproduction of Viruses • In 1952, Hershey and Chase used radioactive elements to differentially label the DNA core and protein capsid of a phage. • Results indicated DNA, not the protein, enters the host, where viral reproduction takes place. Mader: Biology 8th Ed.

  8. Hershey and Chase Mader: Biology 8th Ed.

  9. Structure of DNA • Nucleotide Data • DNA contains: • Two with purine bases • Adenine (A) • Guanine (G) • Two with pyrimidine bases • Thymine (T) • Cytosine (C) Mader: Biology 8th Ed.

  10. Chargaff’s Rules • The amount of A, T, G, and C in DNA varies from species to species. • In each species, the amount of: • A=T • G=C • Complementary base pairing Mader: Biology 8th Ed.

  11. Base Sequence Variability • It has been estimated the human chromosome contains, on average, 140 million base pairs. • Number of possible nucleotide sequences: • 4140,000,000 Mader: Biology 8th Ed.

  12. Watson and Crick Model • James Watson and H. C. Crick constructed a model of DNA for which they received a Nobel Prize in 1962. • Double-helix model is similar to a twisted ladder. • Sugar-phosphate backbones make up the sides. • Hydrogen-bonded bases make up the rungs. Mader: Biology 8th Ed.

  13. Watson and Crick’s DNA Model Mader: Biology 8th Ed.

  14. DNA Replication • Each old strand of DNA serves as a template for a new strand. • Semiconservative - One old strand is conserved in each daughter molecule. • Steps: • Unwinding • Complementary BasePairing* • Joining* * DNA polymerase Mader: Biology 8th Ed.

  15. Meselon and Stahl’s DNA Replication Mader: Biology 8th Ed.

  16. Prokaryotic Versus Eukaryotic Replication • Prokaryotic Replication • Bacteria have a single circular loop. • Replication moves around the circular DNA molecule. • May be able to divide as soon as once every 20 minutes. Mader: Biology 8th Ed.

  17. Prokaryotic Versus Eukaryotic Replication • Eukaryotic Replication • DNA replication begins at numerous origins of replication along the length of the chromosome. • Replication bubbles spread bi-directionally until they meet. • Replication Fork Mader: Biology 8th Ed.

  18. Prokaryotic versus Eukaryotic Replication Mader: Biology 8th Ed.

  19. Replication Errors • A genetic mutation is a permanent change in base sequences. • Some mutations are due to errors in DNA replication, while others are due to to DNA damage. • DNA repair enzymes are usually available to reverse most of these changes. • Genetic variations are the raw material for evolutionary change. Mader: Biology 8th Ed.

  20. Mader: Biology 8th Ed.

  21. Review • Genetic Material • Transformation • Viral Reproduction • Bacteriophages • Hershey and Chase • DNA Structure • Watson and Crick • DNA Replication • Prokaryotic versus Eukaryotic Mader: Biology 8th Ed.

  22. Mader: Biology 8th Ed.

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