Eukaryotic DNA Replication Overview
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Questions and Answers

What is the primary function of DNA polymerase I?

  • Removing RNA primers and replacing them with DNA nucleotides (correct)
  • Synthesizing new DNA strands from RNA templates
  • Sealing nicks in the DNA strand
  • Removal of mismatched nucleotides
  • Which activity of DNA polymerase I is responsible for proofreading newly synthesized DNA?

  • 3′→5′ exonuclease activity (correct)
  • DNA ligase activity
  • 5′→3′ polymerase activity
  • 5′→3′ exonuclease activity
  • How does DNA ligase contribute to DNA replication?

  • It removes RNA primers
  • It catalyzes the formation of phosphodiester bonds (correct)
  • It initiates DNA replication
  • It synthesizes RNA primers
  • What is the error rate of DNA replication, according to the content?

    <p>One mistake per billion nucleotides</p> Signup and view all the answers

    What is a key characteristic of the mismatch repair mechanism?

    <p>It corrects errors after replication is complete</p> Signup and view all the answers

    What initiates DNA replication in eukaryotes?

    <p>Origin recognition complex (ORC) binding to ARSs</p> Signup and view all the answers

    What is the role of the MCM factor in eukaryotic DNA replication?

    <p>It binds to ARSs and acts as a helicase</p> Signup and view all the answers

    What is a characteristic feature of translesion DNA polymerases?

    <p>They create templates with distorted structures and bulky lesions</p> Signup and view all the answers

    What would be the consequence of one error per million base pairs during DNA replication?

    <p>6400 mistakes per cell division</p> Signup and view all the answers

    Which model of DNA replication suggests that one strand remains completely intact while the other is newly synthesized?

    <p>Conservative model</p> Signup and view all the answers

    In Meselson and Stahl's experiment, what type of nitrogen media did E.coli first grow in?

    <p>15N media</p> Signup and view all the answers

    What is the main characteristic of the semiconservative replication model?

    <p>Each daughter strand consists of one old and one new strand</p> Signup and view all the answers

    Which replication mode involves a replication fork and is typically bidirectional?

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

    What is the primary characteristic of discontinuous replication?

    <p>It involves synthesis in segments called Okazaki fragments.</p> Signup and view all the answers

    What is the role of replicons in DNA replication?

    <p>They are units of replication associated with origins.</p> Signup and view all the answers

    Which enzyme is primarily responsible for synthesizing the RNA primer during DNA replication?

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

    What do Meselson and Stahl’s results contradict regarding the conservative model?

    <p>Both heavy and light bands were expected after one round.</p> Signup and view all the answers

    What is the role of DNA polymerase III in DNA replication?

    <p>It adds new nucleotides in the 5′→3′ direction.</p> Signup and view all the answers

    Which protein is responsible for unwinding the DNA helix during replication?

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

    Which of the following statements is true regarding DNA replication speed in E.coli?

    <p>DNA is replicated at 1000 nucleotides/second.</p> Signup and view all the answers

    What is the significance of the 3′-OH group in DNA replication?

    <p>It serves as a site for adding new nucleotides.</p> Signup and view all the answers

    How does DNA polymerase I contribute to DNA replication?

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

    Which component is essential for the formation of the replication bubble at the origin of replication?

    <p>DnaA protein</p> Signup and view all the answers

    What role does DNA ligase fulfill during DNA replication?

    <p>It connects nicks between DNA fragments.</p> Signup and view all the answers

    What is required for the formation of new nucleosomes following DNA replication?

    <p>Disruption of original nucleosomes and redistribution of pre-existing histones</p> Signup and view all the answers

    What role does telomerase play during DNA replication?

    <p>It adds DNA to the ends of chromosomes to prevent shortening</p> Signup and view all the answers

    What would most likely occur if an organism's telomerase were mutated to be nonfunctional?

    <p>Chromosomes would shorten with each generation</p> Signup and view all the answers

    How does DNA replication in eukaryotic cells differ from that in bacteria?

    <p>Histone proteins assist in the organization of DNA in eukaryotes</p> Signup and view all the answers

    Which statement accurately describes the location of DNA replication in eukaryotic cells?

    <p>DNA polymerase is fixed in location and the template DNA is threaded through it</p> Signup and view all the answers

    What is a primary consequence of the end replication problem in linear chromosomes?

    <p>Gaps would persist at the ends of chromosomes after replication</p> Signup and view all the answers

    Which component is NOT involved in the extension of telomeres during DNA replication?

    <p>Histone proteins</p> Signup and view all the answers

    What happens to nucleosomes immediately after DNA replication?

    <p>They are assembled back quickly</p> Signup and view all the answers

    What is the main feature of theta replication in bacteria?

    <p>It features bidirectional replication from a circular DNA.</p> Signup and view all the answers

    Which of the following requirements is NOT needed for linear eukaryotic DNA replication?

    <p>Protein synthesis machinery</p> Signup and view all the answers

    In which direction do DNA polymerases add nucleotides during DNA synthesis?

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

    What characterizes the replication fork during eukaryotic DNA replication?

    <p>The two strands are replicated in opposite directions.</p> Signup and view all the answers

    What is a significant characteristic of rolling-circle replication?

    <p>The outside strand of the circle is displaced during replication.</p> Signup and view all the answers

    How many origins of replication are typically found in linear eukaryotic DNA?

    <p>Hundreds to thousands</p> Signup and view all the answers

    What type of DNA replication occurs in a semiconservative manner?

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

    Which component is critical for the phosphodiester bond formation in DNA replication?

    <p>Tri phosphate nucleotides</p> Signup and view all the answers

    Study Notes

    Eukaryotic DNA Replication

    • Similar to bacterial replication, but differs in several aspects
    • DNA is complexed with histone proteins in nucleosomes
    • Nucleosomes quickly reassemble following replication
    • Creation of nucleosomes requires:
      • Disrupting original nucleosomes on the parental DNA
      • Redistributing pre-existing histones on the new DNA
      • Adding newly synthesized histones to complete the formation of new nucleosomes

    Location of Eukaryotic DNA Replication

    • DNA polymerase is fixed, and template RNA is threaded through it

    Replication at the Ends of Chromosomes

    • Telomeres and telomerase are involved
    • If telomeres were not replicated by telomerase, chromosomes would shorten after each replication
    • Telomerase replicates the ends of chromosomes
      • G-overhang
      • Contains protein and RNA components
      • Extends the telomere after polymerase sees a 3' OH and extends

    Replication at the Ends of Chromosomes - Telomerase

    • Unclear how the other strand is synthesized

    Telomerase Mutation

    • If telomerase were mutated and nonfunctional, chromosomes would shorten each generation

    DNA polymerase I

    • 5' to 3' polymerase and 3' to 5' exonuclease activities
    • Primarily used for removing RNA primers and replacing them with DNA nucleotides
    • 5' to 3' exonuclease activity is used to remove primers laid down by primase and to replace them with DNA nucleotides
    • Takes out RNA nucleotides and puts in DNA nucleotides

    DNA polymerase I and DNA Ligase

    • 5' to 3' exonuclease activity removes primers and replaces them with DNA nucleotides
    • DNA ligase creates a phosphodiester bond without adding another nucleotide to the strand
    • All that is left is DNA

    Bacterial DNA Replication

    • Requires a large number of enzymes and proteins
    • Replication fidelity is high (less than one mistake per billion nucleotides)
    • Proofreading: DNA polymerase I's 3' to 5' exonuclease activity removes incorrectly paired nucleotides
    • Mismatch Repair: corrects errors after replication is completed
      • Distinguishes between old and new strands of DNA to determine which base to remove
    • Termination occurs when replication forks meet or by a termination protein.

    Eukaryotic DNA Replication

    • Aut autonomously replicating sequences (ARSs) are 100-120 bps long (origin of replication)
    • Origin-recognition complex (ORC) binds to ARSs to initiate replication
    • Replication is licensed by the replication licensing factor
    • MCM (Minichromosome maintenance) binds DNA and initiates replication as a helicase on all origins
    • Eukaryotic DNA polymerase

    Genetic Information must be Accurately Copied

    • One error per million base pairs leads to 6400 mistakes each time a cell divides
    • Replication occurs at high speed in E.coli (1000 nucleotides per second)

    DNA Replication Models

    • Conservative Replication Model
    • Dispersive Replication Model
    • Semiconservative Replication

    Meselson and Stahl’s Experiment

    • Distinguished between isotopes of nitrogen used in nucleotides
    • E.coli was grown in 15N media, then transferred to 14N media
    • Cultured E.coli were subjected to equilibrium density gradient centrifugation

    Meselson and Stahl’s Experiment- Centrifugation

    • Heavier 15N will sink to the bottom
    • Conservative replication model predicts one heavy and one light band after one round of replication

    Modes of Replication

    • Replicons: Units of replication
      • Have one origin of replication in bacteria, and many in eukaryotic chromosomes
    • Theta Replication: In circular DNA (E.coli)
      • Single origin of replication forms a replication fork, and the replication is bidirectional
    • Rolling-Circle Replication: In viruses and F-factor of E.coli
      • Single origin of replication
      • The inside of the circle is a template, and is replicated
      • The outside of the circle is displaced and replicated
    • Linear Eukaryotic Replication: Eukaryotic cells
      • Thousands of origins
      • Replicon is around 200,000- 300,000 bp in length

    Linear Eukaryotic Replication

    • Requires a template strand, raw materials (nucleotides) and enzymes

    Synthesis of New DNA

    • DNA strands are antiparallel: one strand runs 5' to 3' and the other strand runs 3' to 5'
    • DNA polymerases add nucleotides onto the 3' end of the growing strand
    • Replication only goes from 5' to 3'
    • Continuous and discontinuous replication

    Direction of Replication

    • Antiparallel nature of DNA strands means one template is exposed in the 5' to 3' direction and the other in the 3' to 5' direction
    • Synthesis can happen simultaneously on both strands at the fork
    • Continuous replication keeps going
    • Discontinuous replication stops and starts

    Bacterial DNA Replication

    • Initiation proteins: unwind DNA and make a replication bubble (245 bps in the oriC)
      • Initiation protein: DnaA in E.coli
    • Unwinding:
      • Initiator Protein:
      • DNA Helicase
      • Single-strand-binding proteins (SSBs)
      • DNA Gyrase (topoisomerase)

    Initiation of Replication in E.coli

    • DnaA causes the replication bubble to open
    • SSB holds the bubble open

    Unwinding of DNA

    • DNA helicase unwinds DNA
    • Single-strand binding proteins (SSBs) keep the strands separated
    • Topoisomerase relieves tension ahead of the replication fork

    Elongation: DNA Primer Synthesis

    • DNA needs a primer with a 3-OH group to begin
    • Primers are usually 10-12 nucleotides long
    • DNA primase synthesizes an RNA primer

    Elongation: DNA Polymerase III

    • DNA polymerase III is the main workhorse of replication
    • 5' to 3' polymerase activity allows it to add new nucleotides
    • 3' to 5' exonuclease activity allows it to remove nucleotides to correct errors

    Removing RNA Primers: DNA Polymerase I

    • DNA polymerase I removes RNA primers and replaces them with DNA nucleotides
    • DNA ligase connects nicks after the RNA primers are removed

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    Description

    This quiz explores the critical processes involved in eukaryotic DNA replication, highlighting key differences from bacterial replication. It focuses on the role of histone proteins in nucleosome formation and the significance of telomeres and telomerase in maintaining chromosome integrity. Test your knowledge on these fundamental concepts of molecular biology.

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