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DNA Replication and Modification Errors
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DNA Replication and Modification Errors

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Questions and Answers

What type of activity helps reduce replication errors during DNA replication?

  • 5'-3' nuclease activity
  • Helicase activity
  • Editing activity of polymerase
  • 3'-5' nuclease activity (correct)

    • What type of interactions can lead to DNA breaks?

  • Formation of bridges between DNA strands
  • Hydrogen bonds between DNA strands
  • Ionizing radiation (correct)
  • Stable interactions between proteins and DNA

    • What is the direction of DNA synthesis on the leading strand during replication?

  • The direction of synthesis varies
  • 5' → 3' (correct)
  • 3' → 5'
  • It depends on the type of DNA polymerase

    • What is a mutation defined as?

    <p>A transmissible change in genetic material</p> Signup and view all the answers

    What is the function of DNA polymerase I in prokaryotes?

    <p>Eliminating RNA primers and resynthesizing DNA</p> Signup and view all the answers

    What type of mutation involves the substitution of one base pair with another?

    <p>Micro-lesion</p> Signup and view all the answers

    What are the short, discontinuous DNA fragments synthesized on the lagging strand called?

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

    What is the purpose of ligase in DNA replication?

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

    What is an example of a macro-lesion?

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

    Where does DNA replication occur in eukaryotic cells?

    <p>In the nucleus</p> Signup and view all the answers

    What type of mutation occurs when a purine base is replaced with another purine base?

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

    What is a key difference between prokaryotic and eukaryotic DNA replication?

    <p>The complexity of chromatin structure</p> Signup and view all the answers

    What can cause DNA mutations?

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

    How many different DNA polymerases are found in eukaryotic cells?

    <p>5</p> Signup and view all the answers

    What is the result of stable interactions between DNA strands?

    <p>Formation of bridges between DNA strands</p> Signup and view all the answers

    What is the purpose of RNA primers in DNA replication?

    <p>To initiate DNA synthesis</p> Signup and view all the answers

    What is the direction of DNA polymerase activity?

    <p>5' → 3'</p> Signup and view all the answers

    Which DNA polymerase is involved in the replication of the mitochondrial DNA?

    <p>DNA polymerase γ</p> Signup and view all the answers

    What is the function of telomerase in eukaryotic cells?

    <p>Replicating telomeres</p> Signup and view all the answers

    Why do eukaryotic chromosomes have multiple origins of replication?

    <p>Because they need to replicate quickly</p> Signup and view all the answers

    What is the shape of DNA in prokaryotic cells?

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

    Which DNA polymerase is involved in the repair of DNA?

    <p>DNA polymerase ε</p> Signup and view all the answers

    Where does a germline mutation occur?

    <p>In cells that differentiate into gametes</p> Signup and view all the answers

    What is the effect of a point mutation on protein synthesis?

    <p>It may affect one or several amino acids</p> Signup and view all the answers

    What is a transition mutation?

    <p>A replacement of a base by another one of the same chemical category</p> Signup and view all the answers

    What is the result of a deletion or insertion mutation?

    <p>A change in the reading of the DNA sequence</p> Signup and view all the answers

    What is the characteristic of a germline mutation?

    <p>It is present in all cells of the body and is transferable to the offspring</p> Signup and view all the answers

    What is a transversion mutation?

    <p>A replacement of a base by another one of a different chemical category</p> Signup and view all the answers

    What is the effect of a substitution mutation on the DNA sequence?

    <p>It replaces one base pair with another</p> Signup and view all the answers

    What is the result of a point mutation on a codon?

    <p>It may change one or several amino acids</p> Signup and view all the answers

    What is the result of a nonsense mutation?

    <p>A non-functional protein is produced</p> Signup and view all the answers

    What is a characteristic of dynamic mutations?

    <p>They consist of repetitions of some triplets of the DNA</p> Signup and view all the answers

    What is the primary function of electrophoresis in molecular biology?

    <p>To separate DNA, RNA, or protein molecules based on their size and electrical charge</p> Signup and view all the answers

    What is the term for a point mutation that affects a single nucleotide?

    <p>Single Nucleotide Polymorphism (SNP)</p> Signup and view all the answers

    What is the method of Southern (1975) used for?

    <p>Detecting large alterations such as insertions, deletions, or rearrangements</p> Signup and view all the answers

    What is the result of a point mutation that causes a nonsense mutation?

    <p>A non-functional protein is produced</p> Signup and view all the answers

    What is the purpose of PCR in molecular biology?

    <p>To amplify DNA sequences</p> Signup and view all the answers

    What is the term for the repetition of some triplets of the DNA that progresses from one generation to the next?

    <p>Dynamic mutation</p> Signup and view all the answers

    Study Notes

    Modifications of a Database

    • Replication errors: Poly DNAs with 3'-5' nuclease activity can check if the last base is added correctly, reducing possible errors.
    • Formation of bridges: Stable interactions can occur between DNA strands or between proteins and DNA, leading to stable interactions.
    • DNA breaks: Ionizing radiation can cause cleavage of DNA strands or breaks in both strands.

    Types of DNA Mutations

    • Definition of a mutation: A transmissible change in genetic material, concerning germ cells or somatic cells, which can be spontaneous or caused by alterations during replication or DNA repair.
    • Classification of mutations: Macro-lesions (deletions, duplications, amplifications, fusions, inversions, and insertions) and micro-lesions (point mutations, base pair substitutions).

    DNA Replication

    • Elongation of replication:
      • At the leading strand, synthesis occurs in the 5' → 3' direction.
      • At the lagging strand, synthesis is more complicated, occurring in the 5' → 3' direction, but opposite the direction of the fork.
      • Okazaki fragments are formed, and RNA primers are eliminated and replaced with DNA.
      • Finally, DNA fragments are welded by a ligase.

    Replication in Prokaryotes and Eukaryotes

    • Prokaryotes:
      • Replication occurs in the cytoplasm prior to binary fission.
      • Two DNA polymerases (I and III) are involved.
    • Eukaryotes:
      • Replication occurs in the nucleus during S phase.
      • At least five DNA polymerases (α, β, δ, λ, and ε) are involved.
      • Telomeres are replicated by telomerase, and multiple origins are needed.

    Germline Mutation and Classification of Gene Mutations

    • Germline mutation: A mutation that occurs in cells that will differentiate into gametes, becoming hereditary.
    • Classification of gene mutations:
      • Substitution of bases (point mutations):
        • Transition: Replacement of a base by another of the same chemical category.
        • Transversion: Replacement of a base by another of a different chemical category.
      • Mutations by deletion or insertion:
        • Deletion or insertion of one or several nucleotides, causing a change in the reading of the DNA sequence.
      • Nonsense mutations:
        • Produce a stop codon, leading to non-functional proteins.

    Effects of Mutations on the Phenotype

    • Dynamic mutations (triplet repeat expansion mutations):
      • Progress from one generation to another, consisting of important repetitions of some triplets of the DNA.
      • Example: Huntington's chorea.

    Detection of Gene Mutations

    • Methods:
      • PCR (Polymerase Chain Reaction)
      • Molecular hybridization
      • Electrophoresis
      • Southern blotting (for detecting large alterations)
      • Oligonucleotide probes (for detecting point mutations)
      • Direct spotting on a nitrocellulose sheet (dot-blot)

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    Description

    This quiz covers the errors that can occur during DNA replication, including replication errors and the formation of bridges between DNA strands or between proteins and DNA.

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