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DNA Replication and Chromosome Structure in General Biology

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이 집합의 용어 (22)

  • What is the basic principle of DNA replication?
    Each DNA strand acts as a template for building a new complementary strand based on base-pairing rules.
  • What model does DNA replication follow?
    DNA replication follows the semi-conservative model, where each daughter molecule has one parental and one new strand.
  • Where does DNA replication begin?
    Replication begins at specific sites called origins of replication, where the two DNA strands separate to form a replication bubble.
  • What is a replication fork?
    A replication fork is a Y-shaped region at the end of a replication bubble where new DNA strands are elongating.
  • What role do helicases play in DNA replication?
    Helicases untwist the double helix at the replication forks, separating the two DNA strands.
  • What is the function of single-strand binding proteins?
    They bind to and stabilize single-stranded DNA to prevent it from reannealing or being degraded.
  • How does topoisomerase assist DNA replication?
    Topoisomerase corrects overwinding ahead of replication forks by breaking, swiveling, and rejoining DNA strands.
  • What is the role of primase in DNA replication?
    Primase synthesizes a short RNA primer (5–10 nucleotides) that provides a starting point for DNA polymerase.
  • Why can't DNA polymerases initiate DNA synthesis on their own?
    DNA polymerases can only add nucleotides to an existing 3′ end; they require a primer to start synthesis.
  • In which direction do DNA polymerases add nucleotides?
    DNA polymerases add nucleotides only to the free 3′ end, so DNA synthesis proceeds in the 5′ to 3′ direction.
  • 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 away from the fork in Okazaki fragments.
  • What are Okazaki fragments?
    Short DNA segments synthesized discontinuously on the lagging strand, later joined by DNA ligase.
  • How fast is DNA elongation in bacteria and human cells?
    About 500 nucleotides per second in bacteria and 50 nucleotides per second in human cells.
  • What is the role of DNA ligase in replication?
    DNA ligase joins Okazaki fragments on the lagging strand to create a continuous DNA strand.
  • How do DNA polymerases ensure replication accuracy?
    DNA polymerases proofread newly made DNA, replacing incorrect nucleotides to reduce errors.
  • What is mismatch repair in DNA replication?
    Repair enzymes correct errors in base pairing that escape proofreading.
  • What is nucleotide excision repair?
    A nuclease cuts out damaged DNA segments, which are then replaced by DNA polymerase and sealed by DNA ligase.
  • Why are mutations important in evolution?
    Mutations create genetic variation, which is the raw material for natural selection.
  • How is bacterial DNA organized?
    Bacterial chromosomes are double-stranded, circular DNA molecules that are supercoiled and located in the nucleoid region.
  • How is eukaryotic DNA organized in chromosomes?
    Eukaryotic chromosomes have linear DNA molecules tightly packed with proteins into chromatin.
  • What is chromatin?
    Chromatin is the complex of DNA and proteins that condenses to form chromosomes in the nucleus.
  • How do chromosomes fit inside the nucleus?
    Chromosomes are packed through an elaborate multilevel system of folding and coiling.