key term - Direct repair

Definition

Direct repair is a mechanism that corrects damage to nucleotides in DNA without replacing the entire nucleotide. It involves enzymes that directly restore the original structure of the altered nucleotides.

5 Must Know Facts For Your Next Test

1. It primarily deals with single-strand damage, such as thymine dimers caused by UV light.
2. Photoreactivation is a common example of direct repair where photolyase enzyme repairs UV-induced thymine dimers.
3. Direct repair does not require a template strand for correction because it restores the original nucleotide structure.
4. The enzyme methylguanine-DNA methyltransferase (MGMT) can remove alkyl groups from guanine residues, preventing mutagenesis and cytotoxicity.
5. Direct repair mechanisms are highly specific and efficient but limited to certain types of DNA damage.

Review Questions

Related terms

Photoreactivation: A direct repair process where photolyase uses light energy to break covalent bonds in thymine dimers.

Nucleotide Excision Repair: A DNA repair mechanism that removes a short segment of the damaged strand and uses the complementary strand as a template for correction.

Base Excision Repair: A mechanism that fixes small, non-helix-distorting base lesions by removing the damaged base and filling in the gap with correct nucleotides.