DNA Repair and Mutation

Flashcards covering the types of DNA mutations, sources of DNA damage, repair mechanisms, and associated clinical conditions based on the lecture by Asst. Prof. Ziba Abdkarimi.

Mutation

A permanent change in the DNA sequence of a cell that can occur randomly during division or due to external factors.

Point mutation

A type of mutation that involves a change in a single nucleotide base pair.

Silent mutation

A DNA change that does not alter the amino acid sequence, leaving the protein normal.

Missense mutation

A DNA change that results in a different amino acid, which can alter protein function.

Nonsense mutation

A DNA change that creates a premature "stop" signal, resulting in a shortened and usually non-functional protein.

Frameshift mutation

A mutation occurring when one or more nucleotides are inserted or deleted, shifting the reading frame of the codons.

Codons

Groups of three nucleotides in which the genetic code is read.

Endogenous sources

Sources of DNA damage that originate from inside the cell, such as replication errors or metabolism.

DNA polymerase

The enzyme responsible for copying DNA, which includes internal proofreading but can still leave replication errors.

Reactive Oxygen Species (ROS)

Highly reactive molecules produced by normal cellular metabolism that can oxidize DNA bases, leading to structural damage.

Exogenous sources

Sources of DNA damage that come from outside the cell, including radiation and chemical mutagens.

Thymine dimers

Distortions in DNA shape caused by UV radiation causing adjacent thymine bases to bond together.

Ionizing Radiation

High energy radiation like X-rays and gamma rays that can cause double-strand breaks in the DNA backbone.

Chemical Mutagens

Agents such as tobacco smoke or industrial toxins that can bind directly to DNA and alter its chemical structure.

Mismatch Repair (MMR)

A single-strand repair system that fixes errors from DNA replication by identifying and replacing incorrect base pairs on the new strand.

Base Excision Repair (BER)

A mechanism that removes small base lesions, such as oxidized bases, that do not distort the overall DNA helix.

DNA glycosylases

Specific enzymes used in Base Excision Repair (BER) to recognize and cut out damaged bases.

Nucleotide Excision Repair (NER)

A repair mechanism for bulky damage that distorts the double helix, such as thymine dimers, by removing a short segment of nucleotides.

Homologous Recombination (HR)

An error-free double-strand break repair mechanism that uses an identical sister chromatid as a template.

Non-Homologous End Joining (NHEJ)

A fast but error-prone double-strand break repair mechanism that joins broken DNA ends directly without a template.

Xeroderma Pigmentosum

A condition caused by a defect in Nucleotide Excision Repair (NER), resulting in an extreme risk of skin cancer from UV damage.

Lynch Syndrome

A condition caused by a defect in Mismatch Repair (MMR), leading to a high risk of hereditary colorectal cancer.

BRCA Mutations

Mutations in BRCA1 or BRCA2 genes that impair Homologous Recombination (HR), increasing the risk of breast and ovarian cancers.