mutations

define mutation

• change in normal DNA sequence.

• usually neutral — no affect on organism’s fitness

• harmful — responsible for many disorders

beneficial mutations

mutants better adapted to environment → evolution via natural selection

point mutations

• change in 1 nucleotide/base pair in a gene

• can be substitution, insertion, or deletion

• only causes problems in exons

how are point mutations occuring/fixed

• errors are from uncorrected mistake in DNA replication

• insertions fixed by exonucleases

• deletions are rarely reversible

frameshift mutations

• caused by insertion/deletion that’s not factor of 3 nucleotides

• entire “reading frame'“ (codon) altered

silent mutations

codes for the same amino acid, substitution of nucleotide doesn’t change anything, thus “silent”

missense mutations

• codes for a different amino acid

• sickle cell anemia caused by single base pair substitution (missense)

• beneficial in creating new proteins like antibodies to fight new infections

nonsense mutations

• codes for a premature stop codon

• can be lethal to the cell, usually very harmful to the organism

change to chromosome number is…

always detrimental, if not lethal, to an organism

mutations can also involve [_____] which may affect [____] and thus [__] synthesis

mutations can also involve [rearrangement of genetic material which may affect several genes & chromosomes and thus protein synthesis

chromosomal deletion

loss of genes

chromosomal duplications

multiple copies of genes/chromosomes

chromosomal inversion

segment of DNA in a chromosome gets inverted

chromosomal translocation

• trading of chromosomal segments between 2 different chromosomes

• usually not the same size segment being traded

• some forms of cancer are caused by translocation

cause of spontaneous mutations

happen naturally

cause of induced mutations

environmental factors

cause of spontaneous mutation

• DNA rep. errors

• DNA transposition: movement of specific DNA sequences (transposable elements)

mutagen/mutagenic agent

substance/event that increases rate of mutations

induced mutations — physical mutagen

• cause physical dmg to DNA

  • X-Ray — point mutations and chromosomal deletions

  • UV radiation — causes reactions between adjacent pyrimidine bases (dimers)

chemical mutagen

• react chemically with DNA to cause a nucleotide substitution/frameshift mutation. Most are carcinogenic

• may also have a similar structure to a nucleotide but with different base pairing properties

  • nitrites

  • gasoline fumes

  • cigarette smoke

mutations that accumulate too rapidly or are very harmful do not provide a [__]

mutations that accumulate too rapidly or are very harmful do not provide a selective advantage

DNA pol can repair…

errors made in DNA rep

mismatch repair by…

Mut proteins, help reduce replication errors

DNA repair (2 ways)

• photorepair — correct UV dmg, a photolyase uses visible light to cleave the bond made between adjacent pyrimidines

• excision repair enzymes — recognizes & remove many diff forms of dmg, DNA pol rebuild the removed segment