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DNA Structure and Replication in General Biology

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  • What is the molecular basis of inheritance?

    DNA is the molecular basis of inheritance in genetics and genomics.

  • Describe the structure of DNA.

    DNA has a double helix structure with a sugar-phosphate backbone and nitrogenous base pairs forming the rungs.

  • Which nitrogenous bases pair together in DNA?

    Adenine (A) pairs with Thymine (T) via 2 hydrogen bonds, and Cytosine (C) pairs with Guanine (G) via 3 hydrogen bonds.

  • What is Chargaff's Rule?

    Chargaff's Rule states that the percentage of adenine equals thymine (%A = %T) and the percentage of cytosine equals guanine (%C = %G) in DNA.

  • How many base pairs are in the human genome approximately?

    The human genome contains about 3.2 billion base pairs.

  • What are purines and pyrimidines in DNA bases?

    Purines (A, G) have two rings; pyrimidines (C, T) have one ring.

  • Who discovered the double helix structure of DNA?

    James Watson and Francis Crick discovered the double helix structure, building on Mendel's work.

  • What was Rosalind Franklin's contribution to DNA discovery?

    Rosalind Franklin produced Photo 51, an X-ray diffraction image critical to determining DNA's structure.

  • What does semi-conservative replication mean?

    Each new DNA molecule contains one original strand and one newly synthesized strand.

  • How does DNA replication differ in prokaryotes and eukaryotes?

    Prokaryotes have circular DNA with one origin; eukaryotes have linear DNA with multiple origins for faster replication.

  • What is the role of helicase in DNA replication?

    Helicase unwinds DNA at the replication fork by breaking hydrogen bonds.

  • What do single-strand binding proteins (SSBs) do?

    SSBs prevent separated DNA strands from reannealing during replication.

  • What is the function of topoisomerase during replication?

    Topoisomerase relieves torsional stress ahead of the replication fork to prevent DNA tangling.

  • What does primase do in DNA replication?

    Primase synthesizes a short RNA primer to provide a starting point for DNA polymerase.

  • In which direction does DNA polymerase synthesize DNA?

    DNA polymerase synthesizes DNA only in the \(5\to3\) direction.

  • What is the difference between leading and lagging strands?

    The leading strand is synthesized continuously toward the fork; the lagging strand is synthesized discontinuously away from the fork in Okazaki fragments.

  • What is the role of DNA polymerase I?

    DNA polymerase I removes RNA primers and replaces them with DNA nucleotides.

  • What does DNA ligase do during replication?

    DNA ligase seals nicks between Okazaki fragments on the lagging strand.

  • How is replication accuracy maintained?

    Mismatch repair systems correct base-pairing errors shortly after replication.

  • What are telomeres and their function?

    Telomeres are repetitive, non-coding sequences at chromosome ends that protect essential genes from degradation.

  • How do telomeres relate to aging?

    Telomeres shorten with each cell division, contributing to cellular aging and limiting lifespan.