DNA Repair and Recombination - Vocabulary flashcards

Vocabulary flashcards covering key terms from the DNA repair and recombination lecture notes.

Mutagens

Agents that damage DNA.

Radiation

Mutagenic energy sources such as x-rays and UV light.

Benzo[a]pyrene

Chemical mutagen found in cigarette smoke.

Aflatoxins

Natural products (in mushrooms) that are mutagenic.

Carcinogens (as described in notes)

Carcinogens do not directly damage DNA (examples: H. pylori, alcohol, asbestos in notes).

Endogenous mutagens

Mutagens generated by metabolic reactions inside the cell.

Reactive oxygen species (ROS)

Chemically reactive oxygen-containing molecules that cause base oxidation and DNA strand interruptions.

Mismatched base pairs

Incorrect base pairs resulting from errors during replication.

Deamination

Hydrolysis removing an amino group from a base, altering base identity.

Depurination

Loss of a purine base (A or G) from DNA.

Depyrimidination

Loss of a pyrimidine base (C or T) from DNA.

Alkylation of bases

Addition of alkyl groups (often methylation) to bases.

Exogenous mutagens

Mutagens introduced from outside the cell (environmental agents).

UV light

Exogenous mutagen that crosslinks bases and forms pyrimidine dimers.

Pyrimidine dimers

C-C or T-T crosslinks caused by UV light, distorting DNA.

Ionizing radiation

Radiation that causes DNA strand breaks.

DNA adducts

Covalent attachments of mutagenic chemicals to DNA bases.

Intercalating agents

Molecules that insert between base pairs, disrupting replication.

Ethidium bromide

Intercalating agent used as a DNA stain; example of intercalator.

Doxorubicin

Chemotherapeutic intercalating agent used in cancer treatment.

Thalidomide

Intercalating agent listed among mutagen/intercalator examples; used in therapy.

Substitution mutations

One base replaced by another in DNA.

Deletion mutations

Loss of one or more bases from DNA.

Insertion mutations

Addition of one or more bases into DNA.

Transition

Substitution of a purine for a purine (A↔G) or a pyrimidine for a pyrimidine (C↔T).

Transversion

Substitution of a purine for a pyrimidine or vice versa.

Base Excision Repair (BER)

Repair pathway that removes damaged bases via DNA glycosylases, AP endonuclease, and fills/gaps with polymerase and ligase.

DNA glycosylases

Enzymes that remove damaged bases in BER by cleaving the glycosidic bond.

AP endonuclease

Enzyme that cleaves the abasic site created after base removal.

DNA polymerase

Enzyme that fills in the DNA gap during repair.

DNA ligase

Enzyme that seals nicks in the DNA backbone after repair.

Long patch repair

BER pathway variant that uses longer replacement DNA synthesis (displacing).

Short patch repair

BER variant with minimal replacement of a few nucleotides.

Nucleotide Excision Repair (NER)

Repair pathway correcting bulky lesions like pyrimidine dimers; major defense against UV and cigarette smoke damage.

Pyrimidine dimers

Crosslinked cytosine and thymine bases caused by UV exposure.

DNA repair steps (NER)

Nuclease cuts damaged strand at two points; repair synthesis fills gap; ligase seals.

Xeroderma pigmentosum (XP)

Disease caused by failed NER leading to extreme UV sensitivity and cancer risk.

Mismatch Repair (MMR)

Repair pathway recognizing mismatches; bacteria use hemi-methylation to distinguish strands; defects cause diseases like FAP.

Direct Repair

Repair pathway that directly reverses damage, e.g., photoreactivation of pyrimidine dimers by photolyase.

DNA photolyase

Enzyme with cofactors (N5,N10-methenyltetrahydrofolate and FAD) that reverses pyrimidine dimers using light.

Transposons

“Jumping genes” that move within the genome via transposase.

Transposase

Enzyme that cleaves/moves transposons within DNA.

Translocations

Chromosomal breaks that join ends of different chromosomes, causing rearrangements.

Philadelphia chromosome

t(9;22) translocation creating Bcr-Abl fusion gene; tyrosine kinase driving CML.

Bcr-Abl

Fusion tyrosine kinase from Philadelphia chromosome; constitutively active and promotes proliferation.

Imatinib

Small-molecule inhibitor used to treat CML by inhibiting Bcr-Abl kinase.

Crossing-over

Meiotic recombination event exchanging DNA between homologous chromosomes.

Meiosis

Cell division producing gametes with half the chromosome number; site of crossing-over.

Lymphocyte differentiation

Process during which crossing-over occurs for antibody diversity.