Topic 4

• What are the four different nucleotides in DNA?

  A, T, C, G
• What does DNA contain that proteins do not?

  Only four different nucleotides
• What did Griffith's experiment demonstrate?

  A substance transforms living bacteria
• What was the unknown substance in Griffith's experiment?

  A heritable substance from dead S cells
• What did Avery, MacLeod, & McCarty's experiment identify as the transforming substance?

  Nucleic acid fraction
• What did Hershey & Chase's experiment focus on?

  Whether DNA or protein enters bacteria
• What radioactive isotope was used to label proteins in Hershey & Chase's experiment?

  Radioactive sulfur ($^{35}S$)
• What did Friedrich Miescher first purify?

  Nucleic acids
• What did Chargaff's rules state about nucleotide ratios?

  A equals T and C equals G
• What radioactive isotope was used to label DNA in Hershey & Chase's experiment?

  Radioactive phosphate ($^{32}P$)
• What did Franklin's X-ray diffraction reveal about DNA?

  DNA is a helix
• What is the diameter of the DNA helix as found by Franklin?

  About 2 nm
• How often does a complete helical turn occur in DNA?

  Every 3.4 nm
• What did Watson & Crick model about DNA?

  DNA is a double helix
• How are the two strands of DNA oriented in the double helix?

  They are antiparallel
• What holds the two strands of DNA together?

  Hydrogen bonds between complementary bases
• What is the significance of complementary base pairing in DNA replication?

  It allows accurate copying of genetic material
• What is the proposed mechanism for DNA replication by Watson & Crick?

  Semiconservative replication
• What are the three mechanisms of DNA replication?

  1. Conservative
  2. Semiconservative
  3. Dispersive
• What did Meselson & Stahl's experiment confirm about DNA replication?

  It confirmed semiconservative replication
• What is required for DNA replication?

  A template, nucleoside triphosphate, and DNA polymerase
• In which direction does DNA polymerase synthesize DNA?

  5’-to-3’ direction
• What does DNA polymerase require to begin synthesis?

  A primer (starter)
• What is the role of helicase in DNA replication?

  It unwinds the double helix
• What does topoisomerase do during DNA replication?

  Relieves torsional strain from unwinding
• What is the function of single-strand-binding proteins?

  Stabilizes single-stranded DNA regions
• What is the role of primase in DNA replication?

  Synthesizes RNA primers
• What is the main DNA polymerase in replication?

  DNA polymerase III
• What are telomeres in eukaryotic DNA replication?

  Short, non-coding, guanine-rich DNA sequences
• What is the function of DNA ligase?

  Joins the ends of DNA segments
• What are the differences between leading and lagging strands in DNA replication?

  • Leading strand: Continuous synthesis towards the fork
  • Lagging strand: Discontinuous synthesis in fragments (Okazaki fragments)
• What is the role of telomerase in eukaryotic replication?

  Lengthens telomeric DNA at chromosome ends
• How does DNA polymerase proofread newly added nucleotides?

  It replaces mismatched nucleotides
• What is mismatch repair (MMR)?

  Enzymes remove incorrectly paired nucleotides
• What does photorepair specifically target?

  Thymine dimers caused by UV light
• What is nucleotide excision repair?

  Removes and replaces different kinds of damage
• What is the central dogma of molecular biology?

  Information flows from DNA to RNA to protein
• What role does messenger RNA (mRNA) play in gene expression?

  It carries the genetic information for proteins
• What replaces Thymine in RNA?

  Uracil
• How are all RNAs synthesized?

  From a DNA template by transcription