Biology 2101: DNA Replication Origins
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Questions and Answers

What are the short fragments formed on the lagging strand during DNA replication called?

  • Leading fragments
  • Replication fragments
  • Primer fragments
  • Okazaki fragments (correct)
  • The lagging strand is synthesized continuously from 5’ to 3’ direction.

    False

    What enzyme removes the primer sequences during DNA replication?

    Exonuclease

    Replication is termed semi-conservative because the new DNA consists of one _____ and one _____ chain of nucleotides.

    <p>new, old</p> Signup and view all the answers

    Which enzyme is responsible for joining the Okazaki fragments together?

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

    Match the following enzymes with their roles in DNA replication:

    <p>Helicase = Unwinds DNA and breaks hydrogen bonds Exonuclease = Removes primer sequences Ligase = Joins Okazaki fragments DNA Polymerase = Adds complementary bases</p> Signup and view all the answers

    The initiation of DNA replication starts with the attachment of helicase.

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

    What is the result of DNA replication in terms of the genetic makeup of daughter cells?

    <p>Genetically identical</p> Signup and view all the answers

    What is the primary component found at replication origins in DNA that makes it easier to unwind?

    <p>A-T base pairs</p> Signup and view all the answers

    Replication in prokaryotes occurs unidirectionally around the circular chromosome.

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

    How long does it take for E.coli to replicate its genome?

    <p>40 minutes</p> Signup and view all the answers

    The __________are responsible for opening up the DNA helix during the initiation of replication.

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

    Match the following terms with their definitions:

    <p>Leading Strand = Synthesized continuously during replication Lagging Strand = Synthesized in fragments during replication Semi-conservative Replication = Each DNA molecule consists of one new and one old strand Initiator Proteins = Proteins that trigger the beginning of DNA replication</p> Signup and view all the answers

    What is the role of the replisome during DNA replication?

    <p>To replicate DNA bidirectionally</p> Signup and view all the answers

    In prokaryotic DNA replication, the process initiates at multiple origins of replication on circular chromosomes.

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

    What type of replication model is used during DNA replication?

    <p>Semi-conservative replication</p> Signup and view all the answers

    What is the primary characteristic of the leading strand during DNA replication?

    <p>It is synthesized continuously in the direction of the replication fork.</p> Signup and view all the answers

    Okazaki fragments are exclusively associated with the synthesis of the leading strand.

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

    What enzyme is responsible for joining Okazaki fragments?

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

    The process of DNA replication is termed __________ because one original strand is conserved in each new DNA molecule.

    <p>semi-conservative</p> Signup and view all the answers

    Match the following enzymes with their roles in DNA replication:

    <p>Helicase = Unwinds DNA strands Primase = Initiates RNA synthesis DNA ligase = Joins Okazaki fragments Single-stranded binding proteins = Stabilizes unwound DNA</p> Signup and view all the answers

    Where does the replication of both prokaryotic and eukaryotic DNA begin?

    <p>At the origin of replication</p> Signup and view all the answers

    Replication forks move away from the origin of replication in opposite directions.

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

    Name the small, discontinuous pieces of DNA formed on the lagging strand during replication.

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

    Study Notes

    Origin and Initiation of Replication

    • A-T rich regions in DNA are easier to separate and typically found at replication origins.
    • DNA replication begins at a unique sequence known as the origin of replication, which binds initiator proteins that start the replication process.
    • In E. coli, the origin consists of 245 base pairs of DNA where the initiator protein unwinds the DNA.

    Bacterial DNA Replication Model

    • Circular bacterial chromosomes have a replicator near the replication origin.
    • Initiator proteins recruit at the replicator, resulting in melting of the DNA helix and loading of helicase.
    • Assembled replisomes replicate DNA bidirectionally, creating two copies of the bacterial chromosome.

    Prokaryotic DNA Replication

    • Initiation occurs at a single origin of replication, proceeding bidirectionally until complete.
    • Two replication forks form, actively mediating the replication process.

    Synthesis of Leading and Lagging Strands

    • The leading strand is synthesized continuously in the direction of the replication fork.
    • The lagging strand is synthesized in segments called Okazaki fragments, which are made backward relative to the replication fork.

    Role of Proteins in Initiation

    • Helicase and single-stranded DNA-binding proteins unwind and expose the template DNA.
    • Primase synthesizes the leading strands, forming two replication forks moving in opposite directions along the circular chromosome.

    Lagging Strand Replication

    • Numerous primers bind at various points along the lagging strand, initiating the synthesis of Okazaki fragments in the 5' to 3' direction.
    • Exonuclease removes primer sequences, and gaps are filled with complementary bases before ligation occurs, creating a continuous DNA strand.

    Semi-Conservative Nature of DNA Replication

    • DNA replication produces two DNA molecules, each consisting of one new and one original strand, maintaining genetic continuity.
    • After replication, DNA coils into a double helix structure.

    Triggering Replication

    • Initiation of DNA replication involves two steps: the initiator protein unwinds a short stretch of DNA, followed by helicase breaking hydrogen bonds to separate the DNA strands.
    • Helicase continues to unwind the double helix, facilitating replication.

    Genetic Identity Post-Replication

    • Following replication, the cell has double the amount of DNA, allowing for accurate distribution of genetic material into daughter cells, ensuring genetic identity between parent and offspring.

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    Description

    This quiz explores the origin and initiation of DNA replication, focusing on how A-T rich regions are critical for this process. It also includes a model for bacterial DNA replication initiation, providing insights into circular bacterial chromosomes. Test your understanding of these fundamental concepts in molecular biology.

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