Notes ch12 DNA

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Notes ch12 DNA

  1. 1. Chapter 12: DNA
  2. 2. 12.1 The Role of DNA • DNA has 3 functions: – Storing information – Copying information – Transmitting information
  3. 3. 12.2 The Structure of DNA • DNA – deoxyribonucleic acid • Nucleotides – monomers that make up a DNA molecule – 3 parts: • 5 Carbon sugar (deoxyribose) • Phosphate group • Nitrogenous base – Adenine (A) – Guanine (G) – Cytosine (C) – Thymine (T)
  4. 4. Solving the Structure of DNA ∗Edwin Chargaff (1949) ∗Chargaff’s Rule ∗[A]=[T] ∗[C]=[G] Adenine Thymine Guanine Cytosine 35% 45%
  5. 5. • Rosiland Franklin used X-ray diffraction to visualize DNA structure (1952).
  6. 6. • Watson and Crick were the first to model DNA as a double helix in 1953.
  7. 7. The Double Helix Model • All the previous discoveries show us the structure of DNA and how DNA can function as a carrier of genetic information. • Characteristics of the double helix model: – Antiparallel strands – Hydrogen Bonding – Base Pairing
  8. 8. Antiparallel Strands ∗Run in opposite directions Base Pairing ∗Bases are held together by hydrogen bonds. Base Pairing ∗A bonds with T, and C bonds with G ∗ Complimentary base pairs hydrogen bond covalent bond
  9. 9. Practice Base Pairing • If the sequence of bases on one strand of a DNA molecule is TCGAACTGA, the sequence on the other (complimentary) strand is:
  10. 10. 12.3 DNA Replication • Why does DNA replicate? (Hint: Think back to Mitosis) – DNA is replicated in the S phase of the cell cycle, before the cell divides.
  11. 11. Copying the Code • Step 1 – The DNA double helix unwinds • DNA helicase (enzyme). – breaks the H bonds between the bases. • The areas where the double helix separates are called replication forks.
  12. 12. • Step 2 – DNA polymerase (enzyme) moves along each DNA strand adding complimentary bases according to the base pairing rules. – DNA polymerase also proofreads the DNA molecule to reduce errors.
  13. 13. • Step 3 – The process continues until all of the DNA has been copied. – DNA polymerase detaches.
  14. 14. • This process produces two DNA molecules each composed of one new and one original strand. • Both DNA molecules produced are identical to each other. • DNA replication takes place at many points on a eukaryotic chromosome. – Allows replication to happen more quickly.

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