DNA Repair Mechanisms Quiz

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Questions and Answers

Which of the following symptoms is associated with Xeroderma pigmentosum (XP)?

Neurological lesions

Aplastic anemia

Frequent stomach pain

Extreme sensitivity to sunlight (correct)

Ataxia telangiectasia (AT) is caused by hypersensitivity to UV light.

False

What is the genetic inheritance pattern of Lynch Syndrome (LS)?

Autosomal dominant

Individuals with Fanconi's anemia exhibit growth __________________.

retardation Signup and view all the answers

Match the cancer types with their association to Lynch Syndrome (LS):

Colorectal = Yes Endometrial = Yes Ovarian = Yes Skin = No Signup and view all the answers

Which type of excision repair is responsible for correcting bulky lesions in DNA?

Nucleotide excision repair (NER) Signup and view all the answers

DNA polymerases have no proofreading activity.

False Signup and view all the answers

What are the potential consequences of mutations that survive DNA replication mistakes?

They can have no consequence, result in death, lead to genetic disease or cancer, or provide a competitive advantage. Signup and view all the answers

What is one consequence of DNA damage that is not repaired in a timely manner?

It leads to the creation of mutations Signup and view all the answers

Base excision repair (BER) primarily corrects damage to ________ bases.

nitrogenous Signup and view all the answers

Match the following DNA repair processes with their descriptions:

Base Excision Repair (BER) = Corrects damage to nitrogenous bases Nucleotide Excision Repair (NER) = Repairs bulky lesions in DNA Post-replication Repair = Responds when damaged DNA disrupts replication Proofreading Activity = Corrects mismatched base pairs during replication Signup and view all the answers

The process of photoactivation repair is only found in prokaryotic organisms.

False Signup and view all the answers

What does DNA Ligase do in the DNA repair process?

It seals the gap after the appropriate nucleotides are filled in. Signup and view all the answers

The enzyme that absorbs a photon of light for photoactivation repair is called __________.

photoactivation repair enzyme (PRE) Signup and view all the answers

Match the DNA repair steps with their correct descriptions:

Error recognition = The initial damage is identified and cleaved out by a nuclease Nucleotide filling = DNA Polymerase I inserts the appropriate nucleotides Sealing the gap = DNA Ligase closes the repair by sealing the break Signup and view all the answers

Study Notes

DNA Repair Mechanisms

DNA is a stable molecule but can be damaged by environmental factors or replication errors.
Damaged DNA can be quickly repaired, but if not, it becomes a mutation.
Mutations in germline cells are inheritable.

Importance of DNA Repair

Mutations can lead to cancer, genetic diseases, or even death.
DNA repair mechanisms are essential for maintaining genetic integrity and preventing disease.

Photoreactivation Repair

This repair mechanism is found in prokaryotes and eukaryotes.
It directly reverses the formation of thymine dimers caused by UV radiation.
The enzyme photolyase uses blue light to cleave the bond forming the dimer.

Excision Repair

This is a three-step process involving recognition, removal, and replacement of damaged DNA.
Base excision repair (BER) corrects damage to nitrogenous bases caused by spontaneous hydrolysis or chemical alteration.
Nucleotide excision repair (NER) removes bulky lesions that distort the DNA double helix.
Both involve enzymes like nucleases, DNA polymerase I, and DNA ligase.

Mismatch Repair (MMR)

DNA polymerases have proofreading capabilities but some errors may escape during replication.
Mismatch repair enzymes correct these errors, preventing mutations.
Failure to repair mismatches can lead to mutations with varying consequences.

Post-Replication Repair

This repair mechanism is activated when damaged DNA escapes prior repair and disrupts replication.
The RecA protein promotes recombination between the damaged strand and a donor strand.
This creates a gap in the donor strand which is then repaired by DNA polymerase and ligase.

DNA Repair Deficiencies and Diseases

Xeroderma pigmentosum (XP): Caused by defects in DNA repair pathways, particularly those involved in repairing UV-damaged DNA.
Ataxia telangiectasia (AT): Associated with sensitivity to gamma irradiation and defects in DNA repair pathways.
Fanconi’s anemia: Results from a deficiency in repairing DNA cross-links.
Lynch Syndrome (LS): Inherited cancer predisposition syndrome caused by mutations in mismatch repair genes.
LS is associated with a higher risk of developing various cancers, including colorectal, endometrial, gastric, and ovarian cancers.

Lynch Syndrome (LS)

LS is autosomal dominant with variable expressivity, meaning affected family members may have different signs and symptoms.
Mutations in MMR genes (MLH1, MSH2, MSH6, PMS2, or EPCAM) are responsible for LS.
Defects in MMR lead to an accumulation of mutations, increasing the risk of cancer.

Importance of DNA Repair Research

Understanding DNA repair pathways is crucial for developing therapies targeting cancer and other diseases caused by genetic damage.
Further research is necessary to identify new targets for therapeutic interventions and improve existing treatment strategies.

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Description

Test your knowledge on the various mechanisms of DNA repair. Understand the importance of these processes in maintaining genetic integrity and the consequences of mutations. Learn about photoreactivation and excision repair methods, including their specific functions and steps involved.