BLOCK 3: MBG: (3.3) DNA: DNA DAMAGE & REPAIR
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Questions and Answers

What defines a missense mutation?

  • It leads to a codon that codes for a different amino acid. (correct)
  • It results in a premature stop codon.
  • It does not change the amino acid sequence.
  • It involves a shift in the reading frame.

    • Which of the following mutations results in a change of the reading frame?

  • Frameshift mutation. (correct)
  • Silent mutation.
  • Missense mutation.
  • Nonsense mutation.

    • What is the primary consequence of errors during DNA replication?

  • No effect on the DNA sequence.
  • Potential changes in the sequence that affect protein products. (correct)
  • Immediate repair by DNA ligase.
  • Increased fidelity of future replications.

    • Which DNA repair mechanism primarily corrects base pair mismatches introduced during replication?

    <p>Mismatch repair.</p> Signup and view all the answers

    Which environmental factor is known to cause DNA damage through ionizing radiation?

    <p>X-rays.</p> Signup and view all the answers

    What is the primary responsibility of Base Excision Repair (BER)?

    <p>Removing non-helix-distorting changes affecting individual bases</p> Signup and view all the answers

    Which mechanism is directly responsible for fixing thymine dimers caused by UV damage?

    <p>Direct Repair</p> Signup and view all the answers

    How does Nucleotide Excision Repair (NER) recognize DNA damage?

    <p>Through key proteins binding to stalled transcription machinery</p> Signup and view all the answers

    What type of DNA lesion is primarily associated with Homologous Recombination (HR)?

    <p>Double strand breaks</p> Signup and view all the answers

    What distinguishes global genome repair from transcription-coupled repair in NER?

    <p>Global genome repair occurs without association with transcription</p> Signup and view all the answers

    Which DNA repair mechanism can involve repair of interstrand crosslinks?

    <p>Interstrand Crosslink Repair</p> Signup and view all the answers

    What type of mutation is primarily repaired by Mismatch Repair (MMR)?

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

    Which of the following is a consequence of defects in DNA repair mechanisms?

    <p>Increased susceptibility to DNA mutations</p> Signup and view all the answers

    What type of damage does Direct Repair specifically address?

    <p>Altered bases</p> Signup and view all the answers

    Which repair mechanism is linked to cognitive impairment and neurodegenerative diseases?

    <p>Base Excision Repair</p> Signup and view all the answers

    What is an essential feature of Nonhomologous End Joining (NHEJ)?

    <p>It can repair any double strand break</p> Signup and view all the answers

    What characterizes the repair action of Base Excision Repair (BER)?

    <p>It uses DNA N-glycosylases to remove altered bases</p> Signup and view all the answers

    Which of the following processes helps in the repair of bulky, helix-distorting DNA lesions like thymine dimers?

    <p>Nucleotide Excision Repair</p> Signup and view all the answers

    Which of the following is a fundamental component for the recognition of mismatched bases in mismatch repair?

    <p>MutS homologs (MSH)</p> Signup and view all the answers

    What process is directly involved in repairing interstrand crosslinks?

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

    During which step of homologous recombination is the strand from a homologous template used in repair?

    <p>Synthesis of strand</p> Signup and view all the answers

    What is the primary function of nucleotide excision repair (NER)?

    <p>Repair bulky, helix-distorting damage</p> Signup and view all the answers

    Which repair mechanism removes more than one base to correct an error?

    <p>Mismatch repair (MMR)</p> Signup and view all the answers

    Which of the following steps is NOT involved in non-homologous end joining (NHEJ)?

    <p>Strand invasion</p> Signup and view all the answers

    What is one major consequence of errors in DNA replication if not corrected?

    <p>Mutation accumulation</p> Signup and view all the answers

    The repair mechanism that primarily recognizes and repairs double strand breaks is called what?

    <p>Non-homologous end joining</p> Signup and view all the answers

    What type of damage is specifically repaired through the mechanism of base excision repair (BER)?

    <p>Altered bases</p> Signup and view all the answers

    Which of the following mechanisms can cross over with nucleotide excision repair (NER)?

    <p>Homologous recombination</p> Signup and view all the answers

    Which disorder is associated with defective mismatch repair (MMR) mechanisms?

    <p>Cancer predisposition</p> Signup and view all the answers

    What is the central role of exonucleases in mismatch repair?

    <p>Remove mismatched bases</p> Signup and view all the answers

    What is a key feature of non-homologous end joining (NHEJ)?

    <p>Connects broken ends without need for sequence homology</p> Signup and view all the answers

    Which type of damage can lead to stalling during replication and is specifically recognized by interstrand crosslink repair mechanisms?

    <p>Interstrand crosslinks</p> Signup and view all the answers

    What can be a result of reactive oxygen species in the system?

    <p>Endogenous damage to DNA</p> Signup and view all the answers

    Which type of damage is specifically caused by UV light?

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

    Which of the following represents an inappropriate covalent bond formation in DNA?

    <p>Interstrand cross-links</p> Signup and view all the answers

    What role does DNA polymerase play in response to DNA damage?

    <p>It is primarily responsible for the repair processes</p> Signup and view all the answers

    What is a common consequence of teratogens on DNA?

    <p>Leading to frame shifts and base substitutions</p> Signup and view all the answers

    What is the first step in any DNA repair process?

    <p>Identifying the damage</p> Signup and view all the answers

    How do aromatic amines typically cause mutational effects?

    <p>By leading to frame shifts and base substitutions</p> Signup and view all the answers

    Which of the following statements about DNA integrity maintenance is true?

    <p>Cells possess multiple repair mechanisms to handle damage</p> Signup and view all the answers

    What is the primary action involved in all DNA repair mechanisms regardless of type?

    <p>Sealing the DNA backbone</p> Signup and view all the answers

    Which aspect of DNA repair mechanisms tends to show the most diversity?

    <p>The recognition of damaged DNA</p> Signup and view all the answers

    How does direct repair differ from other DNA repair mechanisms?

    <p>It does not involve base replacement</p> Signup and view all the answers

    What is a common limitation of direct repair mechanisms?

    <p>They cannot correct misinserted bases by polymerases</p> Signup and view all the answers

    Which statement accurately describes the first step in repairing DNA damage?

    <p>Recognition of the error</p> Signup and view all the answers

    In the context of DNA repair, what role do polymerases play?

    <p>They replace damaged or removed bases</p> Signup and view all the answers

    What is generally the correct sequence of steps in any DNA repair mechanism?

    <p>Recognize, remove, replace, then seal</p> Signup and view all the answers

    Which component is crucial for the removal of damaged DNA bases?

    <p>Exonuclease or endonuclease activity</p> Signup and view all the answers

    What is the main limitation of base excision repair (BER) compared to nucleotide excision repair (NER)?

    <p>BER can only repair a single base and not larger structures.</p> Signup and view all the answers

    Which of the following best explains why plants, bacteria, and fungi might have evolved distinct DNA repair mechanisms?

    <p>They are exposed to higher levels of UV radiation.</p> Signup and view all the answers

    What type of damage does direct repair primarily target?

    <p>Single base modifications caused by environmental factors.</p> Signup and view all the answers

    In the context of DNA repair, what characterizes the repairs made by nucleotide excision repair (NER)?

    <p>NER deals with large, helix-distorting errors.</p> Signup and view all the answers

    How does base excision repair (BER) identify damaged bases?

    <p>Using specific recognition proteins to identify bad bases.</p> Signup and view all the answers

    What can be inferred about organisms that lack effective DNA repair mechanisms?

    <p>They may have increased rates of mutation and potential failures in vital processes.</p> Signup and view all the answers

    Why is the base excision repair mechanism considered a 'tiny repair' system?

    <p>It can only repair small localized lesions without disrupting the helix.</p> Signup and view all the answers

    What is a potential consequence of a plant's ability to use direct repair mechanisms?

    <p>Enhanced resilience against UV damage.</p> Signup and view all the answers

    Study Notes

    Mutation Types

    • Mutations are classified based on changes to DNA sequence
    • Silent: DNA sequence change but no change in protein sequence
    • Missense: Change in DNA sequence results in different amino acid in a protein
    • Nonsense: Change in DNA sequence causes premature stop codon, resulting in a shortened protein
    • Frameshift: Insertion or deletion of nucleotides that are not a multiple of 3, leading to a shift in reading frame
    • Deleterious: Mutation that negatively affects a cell or organism
    • Beneficial: Mutation that is advantageous for a cell or organism

    DNA Repair Mechanisms

    • Direct Repair: Chemical alteration of a damaged base to restore its original structure
    • Base Excision Repair (BER): Removal of damaged bases by DNA glycosylases
    • Nucleotide Excision Repair (NER): Removal and replacement of damaged DNA segments
    • Mismatch Repair (MMR): Correction of mismatched base pairs during DNA replication
    • Interstrand Crosslink Repair (ICL): Repairs crosslinks between DNA strands
    • Homologous Recombination (HR): Repair of double-stranded breaks using a homologous template
    • Non-homologous End Joining (NHEJ): Joining of broken DNA ends without requiring homology

    Errors during Replication

    • Tautomeric Shifts: Temporary changes in base structure (e.g., keto-enol, amino-imino)
    • Spontaneous Deamination: Loss of an amino group from a base (e.g., cytosine deaminates to uracil)

    Exogenous DNA Damage

    • Ionizing Radiation: Creates double-strand breaks, base modifications, and crosslinks
    • UV Damage: Forms thymine dimers
    • Alkylating Agents: Add alkyl groups to bases, causing mutations
    • Polycyclic Aromatic Hydrocarbons: Create bulky adducts that disrupt DNA structure

    Endogenous DNA Damage

    • Reactive Oxygen Species (ROS): Generated during metabolism, causing base modifications and strand breaks
    • Replication Errors: Mistakes during DNA synthesis

    Consequences of Mutations

    • Changes to DNA structure and sequence
    • Altered protein structure and function
    • Potential for further mutations
    • Disease development
    • Beneficial adaptation

    DNA Damage and Repair

    • Reactive oxygen species (ROS) and external sources like UV radiation can damage DNA.
    • UV light damages DNA by creating thymine dimers.
    • Covalent bonds can form between bases in the same strand or across two strands, interfering with DNA replication.
    • Teratogens are substances that can damage a developing fetus.
    • Toxins, aromatic amines, and environmental stress can all damage DNA.
    • Major categories of DNA damage include:
      • Base modifications (e.g., covalent bonds between bases)
      • Base misincorporation (wrong base inserted)
      • DNA breaks
      • Bulky lesions (large molecules attached to DNA)
    • DNA repair mechanisms are essential for maintaining DNA integrity.
    • Repair mechanisms involve:
      • Damage recognition
      • Damage removal (often by exonucleases or endonucleases)
      • DNA synthesis (using DNA polymerases)
      • Ligation (sealing the DNA backbone)

    DNA Repair Mechanisms

    • Direct repair is a mechanism which directly fixes a damaged base without removing it.
      • Plants use this mechanism to repair UV damage.
      • Human cells typically use other repair mechanisms.
    • Base excision repair (BER) is a major repair mechanism that removes damaged or mismatched bases.
      • Targets single-base lesions.
      • BER cannot handle damage that distorts the DNA helix.
    • Nucleotide excision repair (NER) removes larger lesions that distort the DNA helix.
      • Targets damage that affects multiple bases.
    • Key differences between BER and NER:
      • Target lesions: BER focuses on single-base lesions, while NER targets larger, helix-distorting lesions.
    • Recognition is the most important difference between various repair mechanisms. The ability to recognize specific types of DNA damage is essential for proper repair.

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    Description

    This quiz covers essential concepts related to mutation types and DNA repair mechanisms. It explores different mutation classifications, including silent, missense, and frameshift mutations, alongside DNA repair processes such as direct repair and nucleotide excision repair. Test your understanding of these fundamental topics in genetics.

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