Induced DNA Damage and Mutagens
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Questions and Answers

What is defined as a permanent alteration in the chemical nature of a DNA sequence?

  • DNA mutation
  • DNA replication
  • DNA transcription
  • DNA damage (correct)

    • Which type of DNA damage occurs naturally without external factors?

  • Transitional DNA damage
  • Induced DNA damage
  • Acquired DNA damage
  • Spontaneous DNA damage (correct)

    • What effect does a tautomeric shift have on DNA base pairing?

  • It causes base pairs to disassociate completely.
  • It stabilizes the normal DNA base pairing.
  • It alters the base pairs leading to mismatches. (correct)
  • It changes the chemical structure of the base pairs.

    • In the tautomeric shift, which amino form converts into an imino form?

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

    What type of mutation occurs due to a tautomeric shift?

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

    How does DNA damage differ from a mutation?

    <p>DNA damage changes the chemical structure, while mutation changes the sequence.</p> Signup and view all the answers

    What causes lesions in DNA?

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

    Which of the following is NOT a mode of DNA damage?

    <p>Polymerase-induced damage</p> Signup and view all the answers

    What base does Cytosine deaminate into during spontaneous deamination?

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

    What type of bond is broken during spontaneous depurination, leading to DNA damage?

    <p>Glycosidic bond</p> Signup and view all the answers

    Which of the following is a result of the deamination of Adenine?

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

    Which nitrogen base does Xanthine not pair with after deamination?

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

    What is the effect of a temperature rise above 45 °C on DNA?

    <p>Breaks Glycosidic bonds</p> Signup and view all the answers

    What does the formation of an apurinic site in DNA often lead to?

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

    Which base pair is formed after the deamination of Cytosine?

    <p>Hypoxanthine - Uracil</p> Signup and view all the answers

    What type of mutation primarily occurs due to spontaneous deamination and depurination?

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

    Which type of radiation is characterized as high energy and causes double or single stranded breaks in DNA?

    <p>Ionizing Radiation</p> Signup and view all the answers

    What is the effect of non-ionizing radiation like UV-B on DNA?

    <p>It forms covalent bonds between adjacent pyrimidines.</p> Signup and view all the answers

    Which chemical agent acts by adding an alkyl group to DNA bases and can interfere with DNA replication?

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

    What is a common outcome of DNA damage caused by both physical and chemical agents?

    <p>Formation of lethal mutations.</p> Signup and view all the answers

    Which of the following correctly identifies the base pair involved in thymine dimer formation?

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

    What role does UV-C radiation play in mutagenesis?

    <p>Is absorbed by the ozone layer.</p> Signup and view all the answers

    What is the structural outcome when two thymine bases bond covalently due to UV-B radiation?

    <p>Development of a cyclobutane ring.</p> Signup and view all the answers

    Which of the following best describes a key characteristic of ionizing radiation compared to non-ionizing radiation?

    <p>It can penetrate biological tissues deeply.</p> Signup and view all the answers

    What is the primary effect of reactive oxygen in aerobic cells?

    <p>It converts guanine to 8-oxo guanine.</p> Signup and view all the answers

    What type of mutation occurs due to oxidative damage?

    <p>Transversion mutation.</p> Signup and view all the answers

    What mechanism leads to slippage errors during DNA replication?

    <p>Sliding of DNA polymerase over repetitive sequences.</p> Signup and view all the answers

    Which condition is associated with a slippage error in the Huntington gene?

    <p>An increase in CAG repeat length.</p> Signup and view all the answers

    What external factors can induce DNA damage?

    <p>Mutagens like UV rays and carcinogens.</p> Signup and view all the answers

    How does the PCNA clamp affect DNA polymerase during replication?

    <p>It prevents DNA polymerase from slipping.</p> Signup and view all the answers

    What role does 8-oxo guanine play in DNA damage?

    <p>It can pair with adenine instead of cytosine.</p> Signup and view all the answers

    What is a consequence of slippage errors in the Huntington gene?

    <p>Production of an abnormal Huntington protein.</p> Signup and view all the answers

    Study Notes

    Induced DNA Damage

    • Induced DNA damage occurs due to the presence of mutagens
    • Mutagens can be physical agents like radiations, chemical agents, or biological agents
    • Physical agents like radiations can break DNA strands or lead to dimer formation
    • Radiations come in two types: ionizing and non-ionizing
    • Ionizing radiation is high energy and damages DNA by breaking phosphodiester bonds.
    • Examples of ionizing radiation include alpha, beta, gamma rays, and X-rays
    • Non-ionizing radiation is low energy and promotes covalent bond formation between neighboring bases
    • Excessive exposure to UV-B radiation causes thymine dimer formation, restricting the binding of adenine to thymine.
    • This leads to the formation of apurinic sites (AP site), where a purine base is missing.
    • UV-C radiation also causes mutations but is absorbed by the ozone layer
    • UV-A radiation is used for vitamin A synthesis.

    Chemical Agents

    • Alkylating agents can add alkyl groups (-CH3) to DNA bases, like o-6 methyl guanosine
    • This methylation interferes with the unwinding of the DNA molecule during replication, often causing lethal mutations

    Spontaneous DNA Damage

    • This type of damage occurs naturally in the absence of any external factors
    • Spontaneous DNA damage can occur due to tautomeric shifts, deamination, depurination, and oxidative damage

    Tautomeric Shifts

    • This occurs when the amino form of bases is converted into the imino form (NH2 group converted to =NH)
    • Likewise, the keto form is converted into the enol form
    • These tautomeric forms are similar to the normal bases and escape proofreading mechanisms
    • Tautomeric shifts lead to transition mutations where a purine is replaced by another purine

    Spontaneous Deamination

    • In oxygen-rich environments, bases can undergo deamination
    • Deamination of cytosine leads to the formation of uracil
    • This causes transition mutations

    Spontaneous Depurination

    • It occurs due to the breakage of the glycosidic bond between sugar and nitrogen bases
    • The glycosidic bond is weaker and can easily break at temperatures above 45°C
    • Depurination leads to the formation of apurinic sites (AP) on DNA
    • This causes transition mutations

    Spontaneous Oxidative Damage

    • Reactive oxygen present in aerobic cells can lead to the formation of H2O2 and -OH radicals.
    • These radicals can act on guanine and convert it to 8-oxo guanine.
    • Oxidative damage leads to transversion mutations, where a purine is replaced by a pyrimidine and vice versa.

    Slippage Errors

    • Slippage errors are caused by sliding of the DNA polymerase
    • It is most commonly seen during replication of repetitive sequences present in telomere regions
    • Normally, the PCNA clamp prevents polymerase slippage
    • However, the polymerase can slip from DNA mistakenly
    • Huntington disease is an example of slippage error, where CAG repeats increase from 20–30 to 40–50, affecting normal Huntington protein production.

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    DNA Damage PDF - B.Sc. III Notes

    Description

    This quiz covers the key concepts of induced DNA damage caused by mutagens, including both physical and chemical agents. Participants will explore the mechanisms of how ionizing and non-ionizing radiation impact DNA, as well as the role of alkylating agents in altering DNA structure. Test your understanding of these critical biological topics.

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