DNA Mutations and Repair Mechanisms

Mutations

are changes in the genetic material of a cell

or virus

Point Mutations

are chemical changes in just one or a few nucleotide

pairs of a gene

Insertions and deletions

are additions or losses of nucleotide pairs in a gene

frameshift mutation

insertion or deletion of nucleotides may alter the reading

frame of the genetic message, producing a

A mutation may alter the sequence within a____and affect the rate of transcription (+/-)

promoter

Mutations may occur in other_____or

operator sites

regulatory elements

Germ-line cells

give rise to

gametes

Somatic cells

are all other body

cells

§ Can occur early or late in

development

§ Gives a genetic mosaic with

patches of mutant tissue

Spontaneous mutations

§ From abnormalities in biological processes, free

radicals/reactive oxygen

§ Rates vary species to species and gene to gene

§ Background mutation rate approximately 1 mutation / million

genes (1 in 106)

Induced mutations

§ Caused by environmental agents

§ Higher rate than spontaneous mutations

Mutagens

chemical or physical agents that alter DNA

Ionizing radiation

has high energy and penetrates deeply to create free radicals

§ X rays and gamma rays

§ Cause deletions or breaks in one or both DNA strands

Nonionizing radiation

has less energy and can only penetrate the surface

§ UV light

Mismatch repair

occurs when

mismatched bases are corrected

after DNA synthesis is complete

proofreading process

reduces the error rate to

about one mistake in 10

million base pairs