DNA Polymerase & Replication
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DNA Polymerase & Replication

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Questions and Answers

What is the main function of DNA polymerase I during DNA replication?

  • To unwind the double helix
  • To proofread the newly synthesized DNA
  • To synthesize the leading strand
  • To replace RNA primers with DNA (correct)

    • Which statement correctly describes the synthesis of the lagging strand during DNA replication?

  • It requires multiple RNA primers to initiate synthesis (correct)
  • It is synthesized in a single long continuous piece
  • It is synthesized before the leading strand
  • It is synthesized continuously in the 5′ to 3′ direction

    • What are Okazaki fragments?

  • Long continuous stretches of DNA synthesized without interruption
  • Pieces of DNA that are removed during mismatch repair
  • Short DNA segments synthesized on the lagging strand (correct)
  • Segments of RNA used during leading strand synthesis

    • How does the antiparallel structure of DNA influence replication?

    <p>The lagging strand is synthesized in fragments opposite to the leading strand</p> Signup and view all the answers

    What role does primase play in DNA replication?

    <p>It synthesizes an RNA primer to initiate DNA synthesis</p> Signup and view all the answers

    What is the primary function of DNA polymerase III during DNA replication?

    <p>To synthesize new DNA strands</p> Signup and view all the answers

    Which strand is synthesized continuously during DNA replication?

    <p>Leading strand</p> Signup and view all the answers

    What are Okazaki fragments?

    <p>Segments of newly synthesized DNA on the lagging strand</p> Signup and view all the answers

    What role does primase play in DNA replication?

    <p>It synthesizes RNA primers for DNA polymerase.</p> Signup and view all the answers

    Which of the following describes the antiparallel nature of DNA strands?

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

    During which phase does primase synthesize RNA primers?

    <p>During DNA replication initiation</p> Signup and view all the answers

    How does DNA polymerase III contribute to the process of linking Okazaki fragments?

    <p>It adds nucleotides to the 3' end of the RNA primer.</p> Signup and view all the answers

    What happens to DNA polymerase III after it has synthesized a fragment?

    <p>It detaches from the DNA template.</p> Signup and view all the answers

    What is the primary role of DNA polymerases in DNA synthesis?

    <p>To add nucleotides to a DNA strand</p> Signup and view all the answers

    In which direction can DNA polymerase synthesize a new DNA strand?

    <p>5′ to 3′ direction</p> Signup and view all the answers

    What is the function of primase during DNA replication?

    <p>To synthesize a short RNA primer</p> Signup and view all the answers

    What are Okazaki fragments?

    <p>Short segments of DNA synthesized on the lagging strand</p> Signup and view all the answers

    How does DNA polymerase I contribute to DNA synthesis?

    <p>It replaces RNA primers with DNA</p> Signup and view all the answers

    Why is the DNA structure described as antiparallel?

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

    What initiates the synthesis of a new DNA strand during replication?

    <p>The RNA primer synthesized by primase</p> Signup and view all the answers

    What triggers the addition of nucleotides to a growing DNA strand?

    <p>The parental DNA serving as a template</p> Signup and view all the answers

    What type of reaction occurs when each nucleotide is added to a growing DNA strand?

    <p>Dehydration reaction</p> Signup and view all the answers

    Which statement accurately describes the leading strand during DNA replication?

    <p>It is synthesized continuously toward the replication fork</p> Signup and view all the answers

    What is the primary function of DNA polymerase I in the process of DNA replication?

    <p>Replacing RNA with DNA in Okazaki fragments</p> Signup and view all the answers

    Which statement accurately describes the synthesis of Okazaki fragments?

    <p>They are synthesized in the 5′ to 3′ direction.</p> Signup and view all the answers

    What role does the RNA primer play in DNA replication?

    <p>It provides a starting point for DNA polymerase.</p> Signup and view all the answers

    How do the leading and lagging strands differ during DNA replication?

    <p>The lagging strand is synthesized in discontinuous segments.</p> Signup and view all the answers

    What property of DNA allows for the formation of Okazaki fragments?

    <p>Antiparallel arrangement of DNA strands</p> Signup and view all the answers

    Why is the synthesis of RNA primers critical in the replication process?

    <p>They provide a starting point for DNA polymerase activity.</p> Signup and view all the answers

    In which cellular process are Okazaki fragments primarily involved?

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

    What happens to Okazaki fragments after they are synthesized?

    <p>They are ligated together to form a continuous strand.</p> Signup and view all the answers

    Which enzyme is responsible for the synthesis of the RNA primer for Okazaki fragments?

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

    What is the directionality of the synthesis of the leading strand during DNA replication?

    <p>5′ to 3′ direction</p> Signup and view all the answers

    Study Notes

    DNA Polymerase & Replication

    • DNA Polymerases add nucleotides to a DNA strand
    • Require a primer to which they can add nucleotides
    • The initial nucleotide strand is a short RNA primer
    • The RNA primer is synthesized by the enzyme primase
    • A primer is short (5-10 nucleotides long), and the 3’ end serves as the starting point for the new DNA strand
    • Each nucleotide that is added to a growing DNA strand is a nucleoside triphosphate
    • As each monomer joins the DNA strand, via a dehydration reaction, it loses two phosphate groups as a molecule of pyrophosphate
    • DNA Polymerase I eventually replaces RNA primers with DNA
    • DNA Polymerase can ONLY build DNA in the 5’  3’ direction on the new strand

    Antiparallel Elongation

    • DNA polymerases add nucleotides only to the free 3′ end of a growing strand
    • Therefore, a new DNA strand can elongate only in the 5′ to 3′ direction
    • Along one template strand of DNA, the DNA polymerase synthesizes a leading strand continuously, moving toward the replication fork
    • To elongate the other new strand, called the lagging strand, DNA polymerase must work in the direction away from the replication fork
    • The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase

    DNA Replication Process

    • Primase makes RNA primer.
    • DNA pol III makes Okazaki fragment 1.
    • DNA pol III detaches.
    • Okazaki Fragment one is primed.
    • DNA pol I replaces RNA with DNA.
    • DNA ligase forms bonds between DNA fragments.
    • The lagging strand is complete.

    Proteins Involved in DNA Replication

    • Helicases: Unwind the DNA double helix, separating the two strands
    • Primase: Synthesizes short RNA primers, which are necessary for DNA polymerase to initiate DNA synthesis.
    • Topoisomerase: Relieves the strain in the DNA molecule caused by unwinding.
    • DNA Polymerase III: Adds nucleotides to the 3' end of a growing DNA strand, synthesizing the new DNA strand, performs most of the DNA synthesis in a cell.
    • DNA Polymerase I: Replaces the RNA primers with DNA nucleotides during replication.
    • DNA ligase: Joins the Okazaki fragments together on the lagging strand, forming a continuous DNA strand.
    • Single strand binding proteins: Bind to single-stranded DNA, preventing them from re-annealing back together until replication is complete.

    The DNA Replication Complex

    • The proteins that participate in DNA replication form a large stationary complex, a “DNA replication machine”
    • The DNA moves through the complex during replication.
    • Primase can act as a molecular break.

    Proofreading & Repairing DNA

    • DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides
    • In mismatch repair of DNA, repair enzymes correct errors in base pairing
    • DNA can be damaged by exposure to harmful chemical or physical agents such as cigarette smoke and X-rays; it can also undergo spontaneous changes
    • In nucleotide excision repair, a nuclease cuts out and replaces damaged stretches of DNA

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    Description

    This quiz covers the key concepts of DNA polymerases and their role in DNA replication. Topics include the synthesis of RNA primers, the function of DNA polymerases, and the directionality of DNA strand elongation. Test your knowledge on the mechanisms involved in DNA replication and the enzymes that facilitate these processes.

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