Spontaneous Mutations
Missense mutation
"different amino acid" - resulting protein may only partially function - termed "leaky" - a single base substiution that changes codon for one amino acid into codon for another amino acid
Silent mutations
"wild-type amino acid" - used to indicate mutation that does not alter protein function - change nucleotide sequence of codon, but not the encoded amino acid
Radiation
- UV - Xrays
Larger mutations
- less common - change in a single base pair - insertions, deletions, inversions, duplication, and translocations of nucleotide sequences
Point mutations
- most commun - from alteration of single pairs of nucleotide - from addition or deletion of nucleotide pairs
Spontaneous Mutations
- occur during replication - happen at a low rate - just a single base pair change in a genetic code can have significant effect on cell
Nonsense mutation
- specifies stop codon, yield shorter protein - converts a sense codon to a stop codon
Transition mutations
AT to GC
Transversion mutations
CG to GC
Alkylating agents
add alkyl groups onto nucleases - nitrosoguanidine adds methyl group to guanine - base pairs with thymine base analogs resemble nucleobases - 5-bromouracil resembles thymine - 2-amino purine resembles adenine
Mutagen
an agent that induces change
Intercalating agents
cause frameshift mutations
X rays
cause single and double strand breaks in DNA - double strand breaks often produce lethal deletions
Nitrous acid effect
changes cytosine to uracil and pairs with adenine instead of guanine
Ethidium bromide
common intercalating agents - likely carcinogen
Conditional mutations
expressed only under certain environmental conditions
UV irradiations
forms thymine dimers - covalent bonds between adjacent thymines - cannot fit into double helix, distorts molecule - replication and transformation stall - mutations results from cell's SOS repair mech.
Flat intercalating molecules
insert between adjacent base pairs in DNA strand and push nucleotides apart, causing errors during replication
Conditional lac operon mutants
map in the operator site and produce altered operator sequences not recognized by repressor - operon is always transcribed and b-galactosidase is always synthesized
Chemical mutations
may cause base substitutions or frameshift mutations
Combination therapy
multiple antibiotics is often used; unlikely cells will simultaneously develop resistance
Mutation rate
probability of mutation each cell division typically between 10^-4 and 10^-12 for a given gene
Mutations in tRNA and rRNA
protein synthesis is always disrupted
Inducted mutations
result form outside influence
Frameshift mutation
results from insertion of deletion of one or two base pairs in the coding region of the gene - impact depends on number of nucleotides and location within protein - three pairs changes on codon - one or two pairs yield mutation - often results in premature stop codon
Mutations can be ____ or ______
spontaneous or induced
Auxotrophic mutant
unable to make an essential macromolecule such as an amino acid or nucleotide - has a conditional phenotype - wile-type strain from which it arose is called prototroph
Chloroquine
used to treat malaria
Reversion
when bacteria change to their original state
