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Molecular Basis of Inheritance - DNA Structure and Replication

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Termini in questo insieme (26)

  • What is the genetic material according to early 20th-century experiments?
    DNA was identified as the genetic material, not protein, based on experiments by Griffith, Avery, McCarty, MacLeod, and Hershey-Chase.
  • What was Frederick Griffith's experiment and its significance?
    Griffith showed that a 'transforming principle' from heat-killed pathogenic bacteria could convert harmless bacteria into pathogenic ones, suggesting genetic material transfer.
  • What did Avery, McCarty, and MacLeod demonstrate in 1944?
    They identified DNA as the transforming substance responsible for heredity, ruling out protein and RNA.
  • What was the Hershey-Chase experiment's key finding?
    They showed that only DNA from bacteriophages enters bacterial cells during infection, confirming DNA as genetic material.
  • What are Chargaff's rules?
    In DNA, the amount of adenine equals thymine, and guanine equals cytosine, supporting base pairing and DNA structure.
  • What did Rosalind Franklin contribute to DNA structure discovery?
    She used X-ray crystallography to produce images showing DNA's helical structure and dimensions.
  • Describe the structure of DNA as proposed by Watson and Crick.
    DNA is a double helix with two antiparallel sugar-phosphate backbones and nitrogenous bases paired inside (A with T, G with C).
  • What are the three components of a nucleotide?
    A nucleotide consists of a phosphate group, a deoxyribose sugar, and a nitrogenous base.
  • What is the difference between purines and pyrimidines?
    Purines (adenine, guanine) have a double ring structure; pyrimidines (cytosine, thymine) have a single ring.
  • Why do purines pair with pyrimidines in DNA?
    Purine-pyrimidine pairing maintains a uniform width of the DNA double helix, consistent with X-ray data.
  • What type of bonds hold nitrogenous bases together in DNA?
    Hydrogen bonds hold complementary bases together: A-T pairs have 2 bonds, G-C pairs have 3 bonds.
  • What is the significance of DNA's antiparallel strands?
    The two strands run in opposite 5’ to 3’ directions, which is critical for replication and base pairing.
  • Where does DNA replication begin in bacteria?
    Replication starts at a specific site called the origin of replication.
  • What is the role of helicase in DNA replication?
    Helicase unwinds and separates the two DNA strands at the replication fork.
  • Why is primase necessary in DNA replication?
    Primase synthesizes an RNA primer to provide a starting point for DNA polymerase III.
  • What is the difference between the leading and lagging strands?
    The leading strand is synthesized continuously toward the replication fork; the lagging strand is synthesized discontinuously away from the fork in Okazaki fragments.
  • What are Okazaki fragments?
    Short DNA fragments synthesized on the lagging strand during replication.
  • What is the function of DNA polymerase I?
    DNA polymerase I removes RNA primers and replaces them with DNA nucleotides.
  • What role does DNA ligase play in replication?
    DNA ligase joins Okazaki fragments by sealing the sugar-phosphate backbone.
  • How do DNA polymerases ensure replication accuracy?
    They proofread newly synthesized DNA and correct mismatched nucleotides, reducing errors to 1 in 10 billion.
  • What is nucleotide excision repair?
    A DNA repair mechanism where damaged DNA is cut out by nucleases and replaced by DNA polymerase and ligase.
  • What problem do telomeres solve in eukaryotic DNA replication?
    Telomeres protect chromosome ends from shortening during replication by providing repetitive sequences.
  • What is the role of telomerase?
    Telomerase extends telomeres in germ cells, preventing loss of important DNA sequences.
  • How is DNA packaged in eukaryotic cells?
    DNA wraps around histone proteins forming nucleosomes, which further coil into higher-order structures to form chromatin and chromosomes.
  • What is heterochromatin?
    Densely packed chromatin that is transcriptionally inactive and difficult to access.
  • How can histone modifications affect DNA packaging?
    Chemical changes to histone tails can alter chromatin structure, influencing gene expression.