Molecular Biology: DNA Structure & Replication
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Questions and Answers

What is the primary function of telomeres?

  • To facilitate protein synthesis
  • To enhance RNA synthesis
  • To delay gene erosion (correct)
  • To increase chromosome number

    • Which strand of DNA undergoes continuous replication?

  • Lagging strand
  • Fragmented strand
  • Leading strand (correct)
  • Discontinuous strand

    • What structure forms the basic unit of chromatin in eukaryotic cells?

  • Histone tail
  • Chromatin fiber
  • Nucleosome (correct)
  • Chromatid

    • During which phase is chromatin highly condensed into visible chromosomes?

    <p>Metaphase</p> Signup and view all the answers

    What characterizes euchromatin compared to heterochromatin?

    <p>Euchromatin is loosely packed and transcriptionally active.</p> Signup and view all the answers

    What role does DNA ligase play in lagging strand replication?

    <p>Join Okazaki fragments</p> Signup and view all the answers

    What is a key feature of the bacterial chromosome structure?

    <p>It is circular and forms the nucleoid.</p> Signup and view all the answers

    How do chromatin remodeling complexes influence gene expression?

    <p>By altering chromatin structure in response to signals</p> Signup and view all the answers

    What happens to transcription machinery when DNA is in a heterochromatin state?

    <p>It is silenced due to restricted access</p> Signup and view all the answers

    What did the transformation principle, demonstrated in Griffith's experiment, indicate about DNA?

    <p>DNA can transfer genetic traits.</p> Signup and view all the answers

    Which statement describes the antiparallel nature of DNA strands?

    <p>One strand runs 3' to 5' while the other runs 5' to 3'.</p> Signup and view all the answers

    What was the conclusion of the Meselson-Stahl experiment regarding DNA replication?

    <p>DNA replication is semiconservative.</p> Signup and view all the answers

    Which type of protein is responsible for adding nucleotides during DNA replication?

    <p>DNA polymerases</p> Signup and view all the answers

    What is the primary role of helicases during DNA replication?

    <p>To unwind the DNA double helix.</p> Signup and view all the answers

    Which mechanism primarily fixes errors that occur during DNA replication?

    <p>Proofreading by DNA polymerases</p> Signup and view all the answers

    What happens to eukaryotic chromosomal DNA during each replication cycle?

    <p>It shortens due to the removal of sections.</p> Signup and view all the answers

    Which nitrogenous base pairs with adenine in DNA?

    <p>Thymine</p> Signup and view all the answers

    What role do single-strand binding proteins play during DNA replication?

    <p>They stabilize unwound DNA strands.</p> Signup and view all the answers

    What is the significance of the double helix structure of DNA?

    <p>It facilitates specific base pairing and DNA replication.</p> Signup and view all the answers

    What does the semiconservative nature of DNA replication ensure?

    <p>Each new DNA molecule contains one old strand and one new strand.</p> Signup and view all the answers

    Which experiment provided evidence that DNA, not protein, is the genetic material?

    <p>Hershey and Chase's experiment</p> Signup and view all the answers

    How do the antiparallel strands of DNA contribute to its function?

    <p>They enable enzymes to read and replicate DNA efficiently.</p> Signup and view all the answers

    Which proteins unwind the DNA double helix during replication?

    <p>Helicases</p> Signup and view all the answers

    What is the primary purpose of nucleotide excision repair?

    <p>To replace damaged DNA segments.</p> Signup and view all the answers

    Which base pairs with guanine in DNA?

    <p>Cytosine</p> Signup and view all the answers

    What effect do telomeres have on chromosomes?

    <p>They delay gene erosion.</p> Signup and view all the answers

    What is unique about the structure of DNA as proposed by Watson and Crick?

    <p>It is a double helix with antiparallel strands.</p> Signup and view all the answers

    Which characteristic distinguishes leading strand replication from lagging strand replication?

    <p>Leading strand synthesis is continuous.</p> Signup and view all the answers

    What is the primary purpose of histone proteins in eukaryotic chromosomes?

    <p>To bind to DNA and form nucleosomes.</p> Signup and view all the answers

    What key feature ensures the accuracy of DNA replication?

    <p>The activity of mismatch repair enzymes.</p> Signup and view all the answers

    How does the structure of euchromatin differ from heterochromatin during interphase?

    <p>Euchromatin is transcriptionally active.</p> Signup and view all the answers

    What occurs to chromatin during the transition to the metaphase stage of cell division?

    <p>Chromatin forms visible chromosomes.</p> Signup and view all the answers

    What role do chromatin remodeling complexes play in gene expression?

    <p>They alter chromatin structure to regulate expression.</p> Signup and view all the answers

    What type of DNA structure do bacterial chromosomes typically have?

    <p>Circular DNA</p> Signup and view all the answers

    What is true about heterochromatin in terms of accessibility for transcription?

    <p>It is densely packed, restricting access.</p> Signup and view all the answers

    Study Notes

    DNA as the Genetic Material

    • DNA, not protein, carries genetic information, confirmed by experiments with bacteria and phages (Griffith's and Hershey-Chase).
    • DNA is a double helix with two antiparallel sugar-phosphate backbones.
    • Nitrogenous bases (A-T, G-C) form hydrogen bonds in the interior of the helix.
    • Antiparallel strands (5' to 3' and 3' to 5') are essential for DNA replication and function.
    • Early experiments with bacteria and phages provided strong evidence for DNA as the genetic material.
    • The transformation principle, as demonstrated by Griffith's experiment, indicated that DNA can transfer genetic traits.
    • Hershey and Chase's experiment with bacteriophages confirmed that DNA is injected into bacteria and carries the genetic material.
    • Watson and Crick's model described DNA's structure as a double helix.

    DNA Replication and Repair

    • DNA replication is semiconservative (Meselson-Stahl): each new DNA molecule contains one original and one new strand.
    • Replication occurs at the replication fork.
    • DNA polymerases synthesize new strands by adding nucleotides.
    • Helicases unwind the DNA double helix.
    • Single-strand binding proteins stabilize unwound strands.
    • Leading strand is continuous, lagging strand is discontinuous (Okazaki fragments).
    • Primase creates RNA primers for both strands.
    • DNA ligase joins Okazaki fragments.
    • Proofreading and repair mechanisms (e.g., mismatch repair, nucleotide excision repair) correct errors in DNA replication.
    • DNA polymerase possesses proofreading capabilities for error correction during replication.
    • Mismatch repair enzymes correct errors that escape proofreading.
    • Nucleotide excision repair removes and replaces damaged DNA segments.
    • These mechanisms maintain DNA integrity and prevent mutations.
    • Telomeres, repetitive sequences at chromosome ends, protect against erosion during replication.
    • Telomerase extends telomeres in germ cells, preserving genetic information.
    • This process is crucial for maintaining chromosome stability over generations.
    • Leading strand replication occurs continuously towards the replication fork.
    • Lagging strand replication is discontinuous, involving Okazaki fragments.
    • Both leading and lagging strand synthesis require RNA primers created by primase.
    • DNA ligase joins Okazaki fragments on the lagging strand.

    Chromosome Structure and Chromatin Packing

    • Bacterial chromosomes are circular and associated with proteins to form the nucleoid.
    • Eukaryotic chromosomes consist of DNA, histones, and other proteins.
    • Nucleosomes are the basic units of chromatin, formed by histones wrapping around DNA.
    • Chromatin exists in different levels of packing (10-nm fiber to 30-nm fiber to highly condensed chromosomes during metaphase).
    • Euchromatin (loosely packed) is accessible for transcription, while heterochromatin (densely packed) is generally inactive.
    • Chromosomes occupy specific territories within the nucleus during interphase.
    • Chromatin remodeling complexes alter chromatin structure for gene regulation.
    • Bacterial species commonly possess a circular chromosome.
    • The bacterial chromosome is associated with proteins and forms the nucleoid.
    • Eukaryotic chromosomes are composed of DNA, histones, and other proteins.
    • Histones attach to DNA to form nucleosomes, fundamental chromatin units.
    • Nucleosomes are components of the 10-nm fiber, a level of DNA packaging.
    • Histone tails project outward, participating in chromatin modification.
    • Chromatin organization involves multiple folding and coiling levels.
    • The 10-nm fiber, a loosely organized structure, represents euchromatin, accessible for transcription.
    • The 30-nm fiber is a more condensed structure.
    • During metaphase, chromatin condenses extensively to form visible chromosomes.
    • In interphase, euchromatin is loosely packed and involved in transcription.
    • Heterochromatin is tightly packed, generally inactive transcriptionally.
    • Chromosomes occupy specific regions within the nucleus during interphase.
    • Chromatin arrangement impacts gene expression and regulation.
    • Euchromatin's accessibility permits transcription machinery's interaction with DNA.
    • Heterochromatin's tightness restricts access, silencing gene expression.
    • Chromatin remodeling complexes modify chromatin structure to regulate gene expression in response to cellular signals.

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    Description

    Explore the essential concepts of DNA as the genetic material and the intricacies of DNA replication. This quiz covers key experiments that established DNA's role, its structural characteristics, and the mechanisms involved in replication and repair. Test your knowledge and understanding of molecular genetics!

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