Mechanism of HR in Human Cancers
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Questions and Answers

Which repair mechanism is specifically designed to correct chemically modified bases in DNA?

  • Mismatch Repair (MMS)
  • Nucleotide Excision Repair (NER)
  • Homologous Recombination (HR)
  • Base Excision Repair (BER) (correct)

    • What type of DNA damage is primarily repaired by Nucleotide Excision Repair (NER)?

  • Bulky lesions like Thymine-Thymine dimers (correct)
  • Double-strand breaks
  • Single-strand breaks
  • Chemical changes in bases

    • Which repair mechanism is responsible for detecting and correcting errors that occur during DNA replication?

  • NHEJ
  • Base Excision Repair (BER)
  • Homologous Recombination (HR)
  • Proof-reading (correct)

    • What is one of the common sources of DNA damage leading to Thymine-Thymine dimers?

    <p>Reactive Oxygen Species</p> Signup and view all the answers

    During DNA replication, which repair mechanism helps in joining broken DNA ends?

    <p>Homologous Recombination (HR)</p> Signup and view all the answers

    Which process can lead to the conversion of cytosine (C) to thymine (T) in DNA?

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

    Which repair mechanism focuses on correcting errors after DNA has been synthesized?

    <p>Proof-reading Mismatch Repair (MMS)</p> Signup and view all the answers

    What is the first step in the repair of double-strand breaks (DSB) through homologous recombination (HR)?

    <p>5’ end digestion to leave 3’ recombinogenic ends</p> Signup and view all the answers

    Which repair mechanism involves the removal of chemically modified bases to prevent point mutations after replication?

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

    What is the function of DNA glycosylase in the Base Excision Repair (BER) mechanism?

    <p>Marking the damaged base with a sugar</p> Signup and view all the answers

    Which proteins' mutations can potentiate human cancers by affecting homologous recombination repair?

    <p>BRCA-1 and BRCA-2</p> Signup and view all the answers

    In double-strand break repair (DSB), which process involves DNA strand exchange between separate DNA molecules?

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

    Which repair mechanism is responsible for repairing Thymine-Thymine dimers induced by U.V. light?

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

    What is the main function of Xeroderma pigmentosum genes in the repair of DNA damage?

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

    What is the final step in the repair of double-strand breaks (DSB) through homologous recombination (HR)?

    <p>Resolution of the Holiday Junction</p> Signup and view all the answers

    Individuals with Xeroderma pigmentosum have a higher predisposition to which types of cancer due to their DNA repair defects?

    <p>Melanomas and Squamous cell carcinomas</p> Signup and view all the answers

    Which repair mechanism involves a proofreading process to correct errors in DNA replication?

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

    In E.coli, approximately how many bases are wrongly matched during replication?

    <p>$1$ base every $10,000$</p> Signup and view all the answers

    In homologous recombination, what is the term used for the cleavage and ligation process that resolves the Holiday Junction?

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

    Which gene mutations can lead to an inherited susceptibility to breast cancer?

    <p><strong>BRCA-1</strong> and <strong>BRCA-2</strong></p> Signup and view all the answers

    Which step involves the opening of the DNA duplex in the Nucleotide Excision Repair (NER) pathway?

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

    'Glycosylation' by DNA glycosylase marks the chemically modified base with what?

    <p>A sugar</p> Signup and view all the answers

    Which protein cleaves off the modified base as part of the Base Excision Repair (BER) mechanism?

    <p>APEI endonuclease</p> Signup and view all the answers

    What is the primary reason for the low mutation rate of 1 every 100 million bases?

    <p>Proof-reading activity of DNA polymerase</p> Signup and view all the answers

    Which repair pathway fixes mistakes that have escaped the proofreading activity of DNA polymerase?

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

    What is the most serious form of DNA damage discussed in the text?

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

    Which repair mechanism is prone to errors and is the most common form in mammalian cells?

    <p>Non-homologous End Joining (NHEJ)</p> Signup and view all the answers

    Which repair pathway is more accurate and only possible when homologous sequences are available?

    <p>Homologous Recombination Repair (HR)</p> Signup and view all the answers

    Which step follows the recognition of double strand breaks by Ku in the NHEJ repair mechanism?

    <p>Recruitment of DNA-PKcs by Ku</p> Signup and view all the answers

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