أسئلة المحاضرة التاسعة جينتكس (قبل التعديل)
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Questions and Answers

What does a permanent change of the base sequence of nucleotides refer to?

  • Chromosomal crossover
  • DNA replication
  • Gene mutation (correct)
  • Transcription process

    • Which of the following best describes the function of DNA repair mechanisms?

  • To facilitate gene expression
  • To replicate DNA
  • To fix mutations in the DNA sequence (correct)
  • To remove non-coding regions

    • Which process is NOT involved in DNA repair?

  • RNA splicing (correct)
  • Base excision repair
  • Nucleotide excision repair
  • Mismatch repair

    • Which statement is true regarding mutations?

    <p>Mutations might lead to beneficial traits.</p> Signup and view all the answers

    What is NOT a common cause of mutations?

    <p>Excessive hydration</p> Signup and view all the answers

    What occurs as a result of breaking a phosphate diester bond in the DNA backbone?

    <p>The DNA strand is fragmented.</p> Signup and view all the answers

    What is a consequence of altered or deleted bases in a DNA sequence?

    <p>The protein's amino acid sequence may remain unchanged.</p> Signup and view all the answers

    Which term describes a mutation that results in changing one codon to another but codes for the same amino acid?

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

    Which of the following statements is false regarding altered bases in DNA?

    <p>They always result in a significant change in protein function.</p> Signup and view all the answers

    What best describes the role of phosphate diester bonds in DNA?

    <p>They connect the sugar molecules of adjacent nucleotides.</p> Signup and view all the answers

    What is the primary role of DNA repair mechanisms?

    <p>To correct damage that occurs to the DNA structure.</p> Signup and view all the answers

    Which of the following statements about DNA repair is false?

    <p>Only specific types of cells possess the ability to repair DNA.</p> Signup and view all the answers

    Which mechanism is commonly involved in the DNA repair process?

    <p>Nucleotide excision repair</p> Signup and view all the answers

    What consequence can result from inefficient DNA repair processes?

    <p>Accelerated aging</p> Signup and view all the answers

    Which of the following is NOT a major type of DNA damage that repair mechanisms address?

    <p>Methylation of histones</p> Signup and view all the answers

    What is the primary function of DNA polymerase beta in DNA repair?

    <p>To fill gaps with correct nucleotides</p> Signup and view all the answers

    Which enzyme is responsible for the ligation process in DNA repair?

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

    What is the order of operations when repairing damaged DNA?

    <p>Nucleotide filling followed by ligation</p> Signup and view all the answers

    What role does DNA ligase play in the context of DNA repair?

    <p>It seals nicks in the DNA backbone</p> Signup and view all the answers

    Which statement about damaged DNA repair is incorrect?

    <p>Ligase removes damaged nucleotides.</p> Signup and view all the answers

    What is the primary role of mismatch repair mechanisms?

    <p>To correct errors made during DNA replication</p> Signup and view all the answers

    What type of repair is base excision repair (BER) specifically responsible for?

    <p>Targeting individual damaged nucleotides for removal and replacement</p> Signup and view all the answers

    Which of the following accurately describes nucleotide excision repair (NER)?

    <p>It removes short oligonucleotides containing damage</p> Signup and view all the answers

    Which statement is true regarding the types of DNA repair mechanisms?

    <p>Nucleotide excision repair can handle a broader range of lesions than base excision repair</p> Signup and view all the answers

    What distinguishes excision repair from mismatch repair mechanisms?

    <p>Excision repair repairs damage caused by external factors, while mismatch repair corrects replication errors</p> Signup and view all the answers

    What is the primary role of DNA ligase in DNA replication?

    <p>To seal breaks left by DNA polymerase</p> Signup and view all the answers

    Which disease is associated with defects in DNA mismatch repair?

    <p>Hereditary Non-Polyposis Colon Cancer (HNPCC)</p> Signup and view all the answers

    What can be concluded about the role of DNA mismatch repair mechanisms?

    <p>They help correct errors during DNA replication</p> Signup and view all the answers

    What is a key consequence of malfunctioning DNA mismatch repair systems?

    <p>Accumulation of mutations leading to cancer</p> Signup and view all the answers

    Which statement accurately describes DNA ligase's function in the DNA replication process?

    <p>It seals nicks to create a continuous DNA strand</p> Signup and view all the answers

    Which type of agent is primarily responsible for causing mutations?

    <p>All of the above</p> Signup and view all the answers

    Which category does NOT typically include environmental factors known to induce mutations?

    <p>Genetic agents</p> Signup and view all the answers

    In the context of mutation types, what is the main distinction between physical, chemical, and biological agents?

    <p>Their mechanism of action</p> Signup and view all the answers

    Which statement best describes the relationship between chemical agents and mutations?

    <p>Chemical agents can interact with DNA and alter its structure</p> Signup and view all the answers

    Which of the following is considered a biological agent that can cause mutations?

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

    What is the primary effect of UV exposure on adjacent pyrimidines in DNA?

    <p>Covalent joining of adjacent pyrimidines</p> Signup and view all the answers

    What structural change in DNA is caused by the formation of thymine dimers?

    <p>Kink or distortion in the DNA helix</p> Signup and view all the answers

    What can occur if thymine dimers in DNA are not repaired?

    <p>Permanent mutation leading to hereditary disorders</p> Signup and view all the answers

    Which of the following best describes a thymine dimer's role in DNA damage?

    <p>Formation of covalent bonds causing structural distortion</p> Signup and view all the answers

    What is a potential long-term consequence of repeated exposure to UV light on DNA?

    <p>Increased likelihood of cancer due to hereditary disorders</p> Signup and view all the answers

    What is the primary function of excision repair mechanisms in DNA?

    <p>To remove and replace nucleotides damaged by exogenous agents</p> Signup and view all the answers

    Which type of repair specifically deals with single base lesions in DNA?

    <p>Base excision repair (BER)</p> Signup and view all the answers

    Which of the following statements best describes nucleotide excision repair (NER)?

    <p>NER removes bulky DNA adducts and helix-distorting lesions.</p> Signup and view all the answers

    What distinguishes base excision repair (BER) from mismatch repair (MMR)?

    <p>BER repairs single nucleotide changes, while MMR corrects mismatched base pairs.</p> Signup and view all the answers

    Which best describes the mechanism by which mismatch repair systems function?

    <p>They identify and excise incorrectly paired bases after DNA synthesis.</p> Signup and view all the answers

    What consequence is primarily associated with marked sensitivity to ultraviolet light?

    <p>High susceptibility to skin damage</p> Signup and view all the answers

    Which of the following is NOT a potential outcome of ultraviolet light exposure?

    <p>Improvement in skin elasticity</p> Signup and view all the answers

    What are the long-term risks associated with continuous exposure to ultraviolet rays?

    <p>Potential for multiple skin cancers</p> Signup and view all the answers

    Which statement accurately reflects the consequences of ultraviolet light sensitivity?

    <p>It can lead to dire health issues such as skin cancers and premature death.</p> Signup and view all the answers

    Which of the following is a characteristic of sensitivity to ultraviolet sunlight?

    <p>Increased development of skin diseases</p> Signup and view all the answers

    What is a potential consequence of ineffective DNA repair mechanisms on cellular function?

    <p>Increased risk of uncontrolled cell division</p> Signup and view all the answers

    Which of the following statements about nucleotide excision repair (NER) is accurate?

    <p>NER removes a short single-strand segment of DNA containing damage</p> Signup and view all the answers

    What is the first step carried out by the DNA mismatch repair nuclease complex when it encounters damaged bases?

    <p>Recognizing and binding to the damaged base</p> Signup and view all the answers

    In the context of base excision repair (BER), what is the primary function of DNA glycosylases?

    <p>To remove damaged bases from the DNA strand</p> Signup and view all the answers

    In the context of DNA mismatch repair, which process occurs after the binding of the nuclease complex?

    <p>Excision of the damaged base or bases</p> Signup and view all the answers

    Which specific activity does the endo then exo nuclease refer to in DNA mismatch repair?

    <p>Initial incision followed by a further excision</p> Signup and view all the answers

    What distinguishes mismatch repair (MMR) from other DNA repair mechanisms?

    <p>MMR identifies and corrects improperly paired nucleotides after replication</p> Signup and view all the answers

    Which of these processes is least likely involved in the repair of DNA double-strand breaks?

    <p>Base excision repair</p> Signup and view all the answers

    What is the role of the DNA mismatch repair nuclease in maintaining genetic integrity?

    <p>It prevents the replication of damaged DNA</p> Signup and view all the answers

    Which of the following scenarios accurately describes a consequence of improper functioning of the DNA mismatch repair nuclease complex?

    <p>Increased mutation rates due to unresolved errors</p> Signup and view all the answers

    Study Notes

    DNA Mutation

    • DNA mutation is a permanent change in the base sequence of nucleotides.
    • Mutations can be categorized by size:
      • Gross mutations occur at the chromosome level.
      • Small mutations occur at the DNA level.
    • Spontaneous mutations arise from uncorrected replication errors.
    • Induced mutations are caused by external mutagens:
      • Physical mutagens (e.g., ionizing radiation like gamma and X-rays, non-ionizing radiation like UV radiation, electromagnetic radiation from mobile phones, satellites and computers).
      • Chemical mutagens (e.g., carcinogens like cigarette smoke).
      • Biological mutagens (e.g., viruses like Hepatitis C Virus (HCV) leading to Hepatocellular carcinoma (HCC), Human papilloma virus (HPV) linked to cervical cancer, bacteria like H. pylori causing gastric cancer).

    Types of DNA Damage

    • DNA damage can lead to breaks in the phosphate diester bonds of the DNA backbone.
    • Base changes or deletions can also occur.
    • Point mutations involve changes in a single codon:
      • Silent mutations do not affect protein production as the amino acid remains the same.
      • Missense mutations lead to a change in one amino acid.
      • Nonsense mutations change a normal codon to a stop codon.
      • Sense mutations change a termination codon to one that codes for an amino acid.
    • UV radiation can cause adjacent pyrimidines to form thymine dimers, distorting the DNA helix.
    • If damage is not repaired, permanent mutations can lead to hereditary disorders.

    DNA Repair

    • DNA repair involves enzymes that scan for damage, recognize it, remove it, and resynthesize the DNA.
    • Enzymes such as endonucleases, exonucleases, DNA polymerase, and ligase are crucial for this process.
      • Endonucleases recognize and cut the damaged strand.
      • Exonucleases remove the damaged section.
      • DNA polymerase fills in the gap.
      • Ligase seals the gap.
    • Mismatch repair corrects errors during replication.
    • Excision repair corrects damage from exogenous agents (e.g., chemical or physical):
      • Base excision repair (BER) corrects base errors (e.g., X-ray errors).
      • Nucleotide excision repair (NER) corrects larger defects like thymine dimers caused by UV radiation or chemical mutagens.
    • Xeroderma pigmentosum (XP) is an autosomal recessive condition caused by the deficiency of a UV-specific endonuclease.
    • XP leads to high sensitivity to sunlight, skin damage, multiple skin cancers, and premature death.

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