Chapter 19: Gene Mutation and DNA Repair, and Recombination

Flashcards reviewing gene mutations, DNA repair mechanisms, and recombination.

Mutation

Any heritable change to the genetic material.

Genomic Instability

Increased frequency of mutations in cell division, a hallmark of cancer cells.

Somatic mutation

Mutation in a non-reproductive cell; is not passed on.

Germ-line mutation

Mutation in an egg/sperm cell; all cells in future zygote will have mutation.

Gene mutation

Small change affecting a single gene.

Chromosomal mutation

Large scale change affecting 1 or more chromosomes.

Transition (base substitution)

A change of a pyrimidine (C, T) to another pyrimidine (C -> T) or a purine (A, G) to another purine (G -> A).

Transversion

Change of a pyrimidine to a purine or vice versa (C -> G).

Indels

Addition or deletion of short sequences of DNA, which can lead to frameshift mutations or in-frame insertions and deletions.

Forward mutation

Wild type to mutant type.

Reverse mutation

Mutant type to wild type.

Missense mutation

Amino acid to different amino acid.

Nonsense mutation

Sense codon to nonsense codon.

Silent mutation

Codon to synonymous codon.

Neutral mutation

No change in function.

Neutral mutation

Mutation that alters amino acid but does not affect the function of the protein.

Loss-of-function mutation

Complete or partial absence of normal protein function.

Gain-of-function mutation

Produces new trait.

Conditional mutation

Mutant phenotype only expressed under certain (restrictive) conditions.

Lethal mutation

Causes premature death.

Suppressor mutation

Hides effect of another mutation (restores wild-type).

Intragenic suppressor

Second mutation is within the same gene as the first mutation.

Intergenic suppressor

Second mutation is in a different gene from the first mutation.

Deleterious mutations

Decrease the chances of survival.

Beneficial mutations

Enhance the survival or reproductive success of an organism.

Mutation rate

Likelihood that a gene will be altered by a new mutation, expressed as the number of new mutations in a given gene per cell generation.

Spontaneous mutations

Result from abnormalities in cellular/biological processes; errors in DNA replication with the underlying cause originating within the cell.

Induced mutations

Caused by environmental agents that alter DNA structure are termed mutagens.

Depurination

Loss of a purine base (A/G) from nucleotide.

Deamination

Loss of an amino group from cytosine.

Tautomeric shift

A temporary change in base structure caused by shift in protons that produces rare forms of bases.

Oxidative stress

An imbalance between the production of ROS and an organism’s ability to break them down.

Expanding nucleotide repeats (TNRE)

Increase in the number of tandem copies of a trinucleotide.

Spontaneous Replication Errors

Strand slippage; unequal crossing over.

Mutagens

Agents that alter the structure of DNA and thereby cause mutations.

Chemical mutagens

Base modifiers, intercalating agents, and base analogues.

Physical mutagens

X-rays, gamma rays, ionizing radiation, UV light.

Deaminating agents

Replace amino groups (-NH2) with keto groups (=O).

Alkylating agents

Mutagens that disrupt appropriate pairing between nucleotides by adding an alkyl group to bases.

Intercalating agents

Contain flat planar structures that intercalate themselves into the double helix, distorting the helical structure.

Base analogues

Become incorporated into daughter strands during DNA replication and disrupt structure.

Ionizing radiation

Includes X-rays and gamma rays which penetrate deeply into biological molecules and create free radicals.

Nonionizing radiation

Includes UV light and cannot penetrate deeply into biological molecules but causes the formation of cross-linked thymine dimers.

Single-strand and Double-strand repair pathways

Direct repair, mismatch repair, base-excision repair, nucleotide-excision repair, HDR, NHEJ.

DNA repair process

An irregularity in DNA structure is detected, the abnormal DNA is removed, and normal DNA is synthesized.

Direct Repair of DNA damage

Photolyase repairs thymine dimers and Alkyltransferase repairs alkylated bases.

Mismatch Repair

During DNA replication an incorrect base may be added to the growing strand by mistake; proteins recognize mismatch and remove section of DNA containing the error.

Base Excision Repair (BER)

Glycosylase removes base and AP endonuclease cuts backbone.

Nucleotide Excision Repair (NER)

Removes and replaces many types of DNA damage that distort DNA structure.