Question

HNPCC has defect in

• A. Nucleotide excisio
• B. Base pair excision
• C. Point mutation
• D. Mismatch repair gene

Answer 1

The Correct Option is D

Hereditary Nonpolyposis Colorectal Cancer (HNPCC), also known as Lynch syndrome, is associated with defects in Mismatch repair gene. The mismatch repair system is crucial for maintaining DNA integrity. It corrects errors that occur during DNA replication by recognizing and repairing erroneous insertions, deletions, and misincorporation of bases.

Here's a brief look at how mismatch repair works:

1. During DNA replication, errors such as mismatched base pairs can occur.
2. The mismatch repair system identifies these errors.
3. Specific proteins cut out the erroneous section of DNA.
4. DNA polymerase fills the gap with the correct nucleotides.
5. Finally, DNA ligase seals the repaired strand.

In HNPCC, this repair process is impaired due to mutations in mismatch repair genes like MLH1, MSH2, MSH6, and PMS2, leading to increased risk of colorectal cancer and other cancers.

Option	Description
Nucleotide excision	Repairs bulky DNA damage
Base pair excision	Removes small, non-distorting lesions
Point mutation	Single nucleotide change
Mismatch repair gene	Corrects base pair mismatches

Thus, the defect in HNPCC is specifically in the mismatch repair mechanism.