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Lecture 9(b)-for xm 3-Molecular Genetics

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  • What did T.H. Morgan's group discover about genes?
    They showed that genes are located on chromosomes and identified DNA and protein as candidates for genetic material.
  • What phenomenon did Frederick Griffith discover in 1928?
    Transformation: a change in genotype and phenotype due to uptake of foreign DNA.
  • What was the key finding of Hershey and Chase's 1952 experiment?
    DNA, not protein, is the genetic material injected by bacteriophages into bacteria.
  • What are the four nitrogenous bases in DNA?
    Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).
  • What is Chargaff's Rule?
    In any species, the amount of adenine equals thymine, and the amount of guanine equals cytosine.
  • What technique did Rosalind Franklin use to study DNA structure?
    X-ray crystallography, which produced images revealing DNA's helical structure.
  • What did Watson and Crick deduce about DNA structure?
    DNA is a double helix with two antiparallel sugar-phosphate backbones and specific base pairing: A with T, G with C.
  • What is the significance of base pairing in DNA replication?
    Each strand serves as a template for a new complementary strand, enabling accurate copying.
  • Describe the semiconservative model of DNA replication.
    Each daughter DNA molecule has one old (parental) strand and one newly synthesized strand.
  • What enzyme unwinds the DNA double helix at the replication fork?
    Helicase untwists the double helix to separate the strands.
  • What role do single-strand binding proteins play in DNA replication?
    They bind and stabilize single-stranded DNA to prevent reannealing.
  • What is the function of primase in DNA replication?
    Synthesizes a short RNA primer to provide a starting point for DNA polymerase.
  • In which direction does DNA polymerase add nucleotides?
    Only to the free 3′ end, synthesizing DNA in the 5′ → 3′ direction.
  • What are Okazaki fragments?
    Short DNA segments synthesized discontinuously on the lagging strand.
  • How are Okazaki fragments joined together?
    DNA ligase joins the fragments by forming phosphodiester bonds.
  • What is the role of topoisomerase during DNA replication?
    Relieves strain ahead of the replication fork by breaking and rejoining DNA strands.
  • How does DNA polymerase proofread newly synthesized DNA?
    It removes incorrectly paired nucleotides and replaces them with correct ones.
  • What is the function of telomeres?
    Protect chromosome ends from erosion during replication by postponing gene loss.
  • What enzyme lengthens telomeres in germ cells?
    Telomerase catalyzes the addition of repetitive nucleotide sequences to telomeres.
  • How do bacterial chromosomes differ from eukaryotic chromosomes?
    Bacterial chromosomes are circular and supercoiled; eukaryotic chromosomes are linear and packaged with histone proteins.
  • What is a nucleosome?
    A bead-like unit of chromatin consisting of DNA wrapped around histone proteins.