Chapter 11: Mutations and DNA Repair

transition mutant

exchange a purine for a purine (A&G) or a pyrimidine for a pyrimidine (C&T)

purine

Adenine and Guanine

pyrimidine

Cytosine and Thymine

transversion mutant

exchange nucleotides outside of nucleotide family; exchange a purine for a pyrimidine

point mutation

gene mutation in which a single base pair in DNA has been changed

synonymous, missense, nonsense, frameshift

categories of point mutations

synonymous mutation (silent mutation)

A base pair substitution that does not change the amino acid that a codon normally produces

missense mutation

A base-pair substitution that results in a codon that codes for a different amino acid

nonsense mutation

A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein

frameshift mutation

mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide

promoter, splice site, and cryptic splice site mutations

categories of regulatory changes

promoter mutation

A mutation altering promoter sequence and function; impacts level of transcription

splice site mutation

Mutation in the coding region of a gene that alters splicing of the mRNA

cryptic splice site mutation

change in the gene sequence, creating a new splice site

intragenic/ compensatory reversion

reversion occurs within the same gene

second site/ suppressor reversion

reversion occurs in different genes

repeat expansion, anomalous base pairing, spontaneous chemical changes

types of DNA replication errors

repeat expansion

a mutation that increases the number of times that the short DNA sequence is repeated. This type of mutation can cause the resulting protein to function improperly.

Fragile X and Huntington's

diseases caused by repeat expansion

Anomalous base pairing

abnormal pairing of bases due to the "wobble" (normal: A-T and G-C)

rare bases, deamination, depurination

types of chemical changes that lead to DNA replication errors

rare bases

bases with structure similar to the normal 4 are incorporated into newly synthesized DNA

Deamination

Removal of an amino group from cytosine converts it to uracil which pairs with adenine during replications resulting in a C-G to T-A transition mutation. A type of spontaneous mutation.

Depurination

the loss of a purine base from a nucleotide

artificial deamination, base analogs, intercalating agents

types of induced chemical mutations

base analogs

structurally similar to normal bases (ex: thymine and 5-bromouracil); can pair normally or mispair

intercalating agents

Planar molecules that mimic base pairs and are able to slip in between the stacked nitrogen bases at the core of the DNA double helix, resulting in insertion or deletion of a single nucleotide pair. A source of induced mutation. can cause frameshift mutations

free radicals

type of radiation (induced mutation) that can alter bases and cause transversion mutations

UV light

type of radiation (induced mutation) that can cause pyrimidine dimers

transposable elements

mobile pieces of DNA that can copy themselves into entirely new areas of the chromosomes

base excision repair (BER)

A DNA repair pathway that involves excision of a damaged base by DNA glycosylase, followed by cleavage of the DNA backbone adjacent to the site by an AP endonuclease. Nick translation, DNA polymerization, and ligation complete the repair.

Nucleotide Excision Repair (NER)

used to repair UV damage and DNA helix distortions; a DNA repair system in which several nucleotides in the damaged strand are removed from the DNA and the undamaged strand is used as a template to resynthesize a normal strand.

mismatch repair

The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.

Double strand break repair

Following phosphodiester bond breakage on both strands of a DNA duplex, a mechanism of DNA damage repair. Related to the mechanism for homologous recombination.

noncomposite transposons

Transposable elements in bacteria that lack insertion sequences