DNA Replication

• What are the four nucleotide bases in DNA?

  Adenine, Guanine, Cytosine, Thymine
• What is the complementary strand to A A G C A T G C?

  T T C G T A C G
• What is the difference between a purine and a pyrimidine?

  Purine is double ringed, pyrimidine is single
• What bond joins the organic base to the pentose sugar in DNA?

  Glycosidic
• What bond joins mononucleotides to form the backbone of DNA?

  Phosphodiester bond
• How do you test for lipids?

  Add ethanol and water, shake for emulsion
• What is the structure of a mononucleotide?

  • Phosphate (ester bond)
  • Pentose sugar (glycosidic bond)
  • Organic base
• Why is DNA replication necessary?

  To ensure daughter cells receive exact genetic copies
• What role does DNA helicase play in replication?

  It unzips the DNA strands by breaking hydrogen bonds
• What happens after DNA helicase completes its function?

  Free nucleotides bind to complementary bases
• What is the function of DNA polymerase in replication?

  It joins activated nucleotides by covalent bonds
• What is the result of DNA replication?

  Two DNA molecules, each with one old and one new strand
• What initiates the replication process on the DNA molecule?

  Replication starts at a specific sequence on DNA
• How do nucleotides attach to the old DNA strands?

  By complementary base pairing with old strands
• What happens to the new DNA strands after they are formed?

  A winding enzyme forms double helices from them
• What does the semi-conservative model of replication state?

  Each daughter molecule contains half old and half new DNA
• Who conducted the experiment proving the semi-conservative model?

  Meselsohn and Stahl
• What isotopes of nitrogen were used in Meselsohn and Stahl's experiment?

  Light $^{14}N$ and heavy $^{15}N$
• How did scientists distinguish between different DNA densities?

  By centrifuging the DNA samples
• What was observed after one generation in the centrifuge experiment?

  Only one band, the 14/15 hybrid
• What was observed after the second generation in the centrifuge experiment?

  Two bands: a light chain and a 14/15 level