gene mutation and dna repair

gene mutation

molecular changes in dna sequence of gene

point mutation

change in a single base pair

involves base substitution

transition

change of a pyrimide to another pyrimidine or purine to purine

transversion

change of pyrimidine to purine (vise versa)

missense mutation

single base mutation that changed amino acid

conservative missense mutation

change of aminnio acids that is chemically similar

nonconservative missesense

change in amino acidds that is chemically different

silent mutation (synomonous)

base substituion that does not alter the amino acid sequncene due to degeneracy of code

wobble position

nonsense mutation

base substition that changes the normal codon to stop codon

framshift mutation

indel (insertion/deletion) of a number of nucleotifes that is not divisible by 3

shift reading fram

inframe mutation

full codon (3 bases) has been added/removed

mutation in promoter

change levels of gene expression

mutation in regulatory elements

distrups ability of gene to be properly regulated

mutation in untranslated region

alter ability of mrna to be translated, alter mrna stability

mutation in splice recognition sequence

alter pre mRNA and unable to slice out intron or take exons out

mutatioin in chromosome structure

expression may be altere to to breaking/rearranging of gene on chromosome

germline mutation

occurs in gametes

passed to half of the gametes

somatic mutation

mutation in normal cell

cannot be passed down

spontaneous mutation

natutally occuring process

1. replication error

2. spontantoes chemical lesion

3. oxidative stress

replication error

nucleotide missparing

strand slipage

spontaneous chemical lesion

depurination: base falling off/breaking of bond

deamination: C ro uracil

induced mutation

caused by enviromental agents

mutagens

alter the structure of DNA

base modifiers

do not pair with approptirate nucleotides i daughter strand during replication

intercalating agent

directly interfers with replication process

base analougues

becomes incorperated into daughter strands during dna replication

physical mutatgens

ionizing raditation

nonionizing radiation

ionizing radiation

x rays

short wavelengher

can cause

• base deletion

• oxidizing bases

• cross linking

• chromosomal breaks

nonionizing radiation

uv light

cause formation of crosslike thymine dimer

dna photolyase

repairs thyamine dimers

alkyltransferase

repaitr methylated bases

DNa polymerase proofreading

mismatch repair

dna methylation distinguish parent and daughter strand

base-excision repair / nucleotide-excision repair mechanism

enzyme finds and removed damaged strand region, dna polymerase resynthesisze region using homology of intact strand, dna ligase fills gaps

nucleotide-excision repair

when double helix is distorted, and multiple bases are removed ( in a row)

Base-excistion repair

nonbulky damages to bases

limited to single base removals

cant deal with distorted helix

Non homologous end joining

repairs double strand breaks, sticks them back together.

error prone, results in small deletion

homologous end joining

repairs double strand break using homology,

use the sisiter chromatid as a template (can only happen after replication)