DNA Damage and Repair Mechanisms

Study Notes

Spontaneous Hydrolysis of DNA

Amine loss can cause DNA mismatches. Cytosine deamination is a common example, changing cytosine to uracil.
Depurination involves the loss of a purine base (guanine or adenine) from the DNA backbone. This creates an abasic site, leading to frameshift mutations.

DNA Damage by Radiation

UV radiation creates DNA photoproducts, mainly thymine dimers, between adjacent pyrimidines. This covalent linkage distorts the DNA backbone, hindering replication and transcription.
Ionizing radiation can cause double-strand breaks in DNA.

Chemical Modification of DNA

Alkylation involves the transfer of methyl or ethyl groups to DNA bases or the phosphate backbone. This can result in base-pair changes during replication if not repaired. Example: alkylation of guanine can cause mispairing with thymine.
Oxidation can occur when DNA reacts with oxygen species. Oxidative damage to guanine can lead to mispairing with adenine.

Base Analogues and Intercalating Agents

Base analogues resemble DNA bases and are incorporated during replication, introducing errors. 5-bromouracil, for example, can replace thymine and mispair with guanine.
Intercalating agents, with polycyclic rings, bind between DNA bases causing insertions or deletions in DNA sequence. These agents distort the DNA structure.

Description

This quiz explores the spontaneous hydrolysis of DNA, the effects of radiation on DNA integrity, and the consequences of chemical modifications such as alkylation and oxidation. Understand how various factors lead to DNA damage and the potential mutations resulting from such alterations.