Question

Describe briefly the mechanism of direct reversal of damage in bacteria.

A) Direct reversal involves excising damaged bases and replacing them with undamaged ones.
B) Direct reversal uses repair enzymes to directly reverse specific types of DNA damage.
C) Direct reversal relies on homologous recombination to reverse DNA damage.
D) Direct reversal only occurs in eukaryotic cells, not bacteria.

Answer 1

Direct reversal of DNA damage in bacteria is achieved by enzymes like photolyase and MGMT, which repair specific types of damage like thymine dimers and methylated guanine bases, respectively, without the need for base excision or use of a homologous template.

Step-by-step explanation:

The mechanism of direct reversal of damage in bacteria involves specific enzymes that act directly on the damaged DNA without the need for excision of bases or reliance on a homologous template. For example, the enzyme photolyase can reverse thymine dimers caused by UV light by using energy absorbed from blue/UV light to cleave the abnormal covalent bond between adjacent thymines. Another enzyme, methyl guanine methyl transferase (MGMT), or its bacterial equivalent OGT, directly reverses methylation damage on guanine bases, but this is a stoichiometric process where each MGMT molecule is used only once. These repair enzymes are highly specific and act without breaking the phosphodiester backbone of DNA, unlike other repair mechanisms like nucleotide excision repair.