Review of Key Concepts - Chapter 15

  1. DNA must encode the information necessary for a cell's survival and specialization and be able to replicate.
  2. Many experiments described DNA and showed it to be the genetic material. Miescher identified DNA in white blood cell nuclei. Garrod connected heredity to symptoms resulting from enzyme abnormalities. Griffith identified a substance that transmits pneumonia to bacteria; Avery, MacLeod, and McCarty showed that the transforming principle is DNA; Hershey and Chase confirmed that the genetic material is DNA and not protein. Levene described the proportions of nucleotide components. Chargaff discovered that A and T, and G and C, occur in equal proportions. Watson and Crick combined these clues to propose the double helix conformation of DNA.
  3. The rungs of the DNA double helix consist of hydrogen-bonded complementary base pairs (A with T, and C with G). The rails are chains of alternating deoxyriboses and phosphates, which run antiparallel to each other. DNA is highly coiled. DNA replication is semiconservative.
  4. DNA unwinds locally at several initiation sites. Replication forks form as hydrogen bonds break between an initial base pair. RNA polymerase builds a short RNA primer, which is eventually replaced with DNA. Next, DNA polymerase fills in DNA bases, and ligase seals the sugar-phosphate backbone. Replication proceeds in a 5{pr} to 3{pr} direction, necessitating that the process be discontinuous in short stretches on at least one strand.
  5. DNA can repair itself in a variety of ways. Photoreactivation splits pyrimidine dimers. Excision repair cuts out the damaged area and replaces it with correct bases. Mismatch repair scans newly replicated DNA for mispairing and corrects the error.

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