Genetics

• What is the hypothesis regarding the genetic transformation of nonvirulent pneumococci?

  Material in dead bacterial cells can genetically transform living bacterial cells.
• What were the results of injecting living S strain and R strain into mice?

  • Mouse dies: Living S strain cells found in heart
  • Mouse healthy: No bacterial cells found in heart
• What conclusion can be drawn from the experiment with pneumococci?

  A chemical substance from one cell is capable of genetically transforming another cell.
• Who determined that a "transforming principle" produced a heritable change in pneumococci?

  Frederick Griffith in 1928.
• What was the hypothesis regarding the chemical nature of the transforming substance from pneumococcus?

  The chemical nature of the transforming substance from pneumococcus is DNA.
• What method did Oswald Avery use to identify the transforming principle?

  He treated samples to destroy different molecules.
• What was the result when DNA was destroyed in Avery's experiment?

  The transforming principle was lost.
• What conclusion was drawn from the experiments involving DNase?

  The transforming substance is DNA.
• What was the purpose of the Hershey-Chase experiment in 1952?

  To determine whether DNA or protein is the genetic material.
• What hypothesis was tested in the Hershey-Chase experiment?

  Either DNA or protein might be the hereditary material that enters a bacterial cell.
• What isotopes were used to label DNA and protein in the Hershey-Chase experiment?

  DNA with $^{32}P$ and protein coat with $^{35}S$.
• What were the results of the Hershey-Chase experiment regarding the location of isotopes?

  $^{32}P$ was found in the pellet (cells) and $^{35}S$ was found in the supernatant fluid.
• What conclusion was drawn from the Hershey-Chase experiment?

  DNA, not protein, enters bacterial cells and directs the assembly of new viruses.
• What are the components that make up DNA?

  DNA is made up of nucleotides, which include deoxyribose, a phosphate group, and a nitrogen-containing base.
• What are the two types of nitrogenous bases found in DNA?

  Purines (adenine and guanine) and pyrimidines (cytosine and thymine).
• What did Chargaff's rule state regarding the amounts of nitrogenous bases in DNA?

  The amount of A equals the amount of T, and the amount of C equals the amount of G.
• What was the significance of X-ray crystallography in determining the structure of DNA?

  • Helped reveal the structure of DNA
  • Inferred the position of atoms by the pattern of diffraction of X-rays
• Who were the key scientists involved in solving the structure of DNA?

  Watson and Crick, using information from Wilkins and Franklin.
• What are the key features of DNA structure?

  • DNA consists of two antiparallel strands
  • A-T pairs and G-C pairs form the rungs
  • Phosphate-sugar chains form the backbones
• What does it mean for DNA strands to be antiparallel?

  The direction of the strands is determined by the sugar-phosphate bonds.
• What is the structure of DNA as established by Watson and Crick in 1953?

  DNA is a double helix.
• What are the three possible models for DNA replication?

  1. Semiconservative replication
  2. Conservative replication
  3. Dispersive replication
• What did Meselson and Stahl demonstrate about DNA replication?

  Semiconservative replication was the correct model.
• How did Meselson and Stahl distinguish parent DNA strands from new DNA strands?

  They used density labeling with $^{15}N$.
• What effect did labeling DNA with $^{15}N$ have on the DNA?


  It made the DNA more dense.
• What is the hypothesis of the Meselson-Stahl Experiment?

  Each DNA strand replicates semiconservatively.
• What was the method used in the Meselson-Stahl Experiment?

  • E. coli grown on a heavy nitrogen medium (¹⁵N)
  • Transferred to normal ¹⁴N
  • Samples taken at 0, 20, and 40 minutes
• What does the result of the Meselson-Stahl Experiment indicate about DNA replication?

  The results can only be explained by the semiconservative model.
• How would the results differ if DNA replication was conservative?

  The first generation would have all been high or low density, but not intermediate.
• What would happen if DNA replication was dispersive according to the Meselson-Stahl Experiment?

  The density in the first generation would be half, but this density would not appear in subsequent generations.
• What is the direction in which the new DNA strand grows?

  The new DNA strand grows by adding to its 3' end.
• What attaches to the 3' end sugar during DNA strand growth?

  A new nucleoside triphosphate attaches to the 3' end sugar.
• What provides energy for the addition of nucleotides during DNA replication?

  Energy from cleaving the pyrophosphate ion binds the nucleotide.
• What is the key enzyme of the DNA replication complex?

  DNA Polymerase is the key enzyme of the replication complex.
• How does DNA polymerase ensure correct base pairing?

  DNA polymerase binds to the template strand and ensures the correct base fits into the new strand.
• What is required to start the new DNA strand?

  A "Primer" is required to start the new DNA strand.
• What synthesizes the RNA primer?

  The primer is synthesized by primase.
• What increases the efficiency of DNA polymerization?

  A Sliding DNA Clamp increases the efficiency of DNA polymerization.
• Why is RNA used for the primer instead of DNA?

  • rNTPs are in higher concentration than dNTPs.
  • RNA serves as a low-fidelity marker for removal.
• What does DNA helicase do during replication?

  DNA helicase uses energy from ATP to unwind the DNA.