mutations

what effects of changes in the DNA sequence have

in general, DNA replication occurs without much error but mistake can occur

mutations aren’t always bad as they can

they can alter the coding portion of the gene, resulting in an aberrantly functioning protein

point mutations

silent: usually in third position of a codon; results in no change in the amino acid sequence of the protein

missense: a change in a codon that results in coding for a different amino acid at that position in the eventual protein

nonsense: a change that forms a stop where on shouldn’t be found

frameshift mutation

insertions or deletions of nucleotides can also result in mutation

changes how a ribosome reads an mRNA molecule

frameshifts often dramatically later amino acid sequences of proteins

inversions and translocation

more extensive DNA alterations

very damaging to a cell

causes of mutations

spontaneous mutations due occur at very low, low rate due to proofreading capability of DNA pol

induced mutations: certain chemical can induce mutations at a higher rate than is found spontaneously; nitrous acid can cause deamination to occur on the DNA; ultraviolet light can also cause a higher than expected mutation rate in DNA (forming thymine dimer)

nucleotide excision repair

uvrAB complex identifies the damaged region; names as such because they are involved in UV light repair of thymine dimers; can also fix other types of damage DNA

uvrA leaves the complex

uvrC binds to uvrB

uvrD will then come in and remove the damaged region, creating a gap

uvrBC endonuclease will make a nick on both sides of the damage region using ATP hydrolysis

DNA polymerase I binds to the gap and resynthesizes the missing nucleotides and DNA ligase seals the nicks

ESSENTIAL

photo reactivation repair

light dependent repair system

the enzyme photolyase recognizes and binds to the thymine dimer

it breaks the bond between the two pyrimidines restoring normal base pairing

are mutations the only way to obtain new genetic materials

no

horizontal gene transfer

the transfer of genetic information between organisms, as opposed to vertical inheritance from parental organisms

transformation

competent cell picks up free DNA from the environment (lysed cells)

if free DNA isn’t incorporated into chromosome (or able to exist as a plasmid) it will be degraded

transduction

bacterial DNA is transferred from one bacterium to another by a virus

bacteriophage injects DNA into host —> DNA is packaged into viral capsid

normally viral DNA is packaged

occasionally, bacterial DNA is packaged by mistake —> transduction

bacterial DNA is transferred to a new host

can bring new bacterial genes to host

conjugations

copy of the genetic information is transferred from one cell to another by cell to cell contact

contact between bacteria is first made with pills

the genetic element that is transferred is usually a plasmid

common way to for bacteria to pick up antibiotic resistance

effects of gene transfer

spreads useful genes among bacteria

antibiotic resistance genes; spread wherever antibiotics are overused (hospitals, farms)

pathogenicity islands: encode genes for cell to act as pathogen; difference between typical E.coli in gut and pathogenic E. coli; able to make toxins that typical E.coli cannot make

genes to degrade special metabolites (oil spills)