M6 - mutations and DNA repair

what are mutations?

heritable changes in genome

what are point mutations?

alteration of - of nucleotides, can be - (two options) of a nucleotide pair

single pair, addition/deletion

what are larger mutations?

- (four options) of nucleotide sequence

they are - (less/more) common

deletions, inversions, duplications and translocations

less

how do mutations occur?

spontaneous and induced

spontaneous mutations arise occasionally in all cells, they - (are/aren’t) caused by an agent

aren’t

induced mutations are due to exposure to a - or - mutagen

chemical, physical

mutations can be classified using - or -

genotypic change, phenotypic consequences

spontaneous mutations result from

• errors in -

  • base tautomerization

  • insertions/deletions due to slippage

• spontaneous - in DNA

• action of mobile genetic elements such as -

all spontaneous errors are corrected by the -

DNA replication, lesions, transposons

DNA repair systems

replication errors usually occur in stretches of - nucleotides

slippage in new strand results in -

slippage in parental strand results in -

repeated

insertion

deletion

base tautomerization is when the nitrogenous base of a nucleotide can shift to a - form

bases are usually in - form, but can shift to - or - forms

tautomeric forms have different - characteristics

tautomeric

keto, imino, enol

H-bonding

base tautomerization results in abnormal -

results in A binding with - and G binding with -

base pairing

C, T

base tautomerization results in - and -

transition: purine for - or pyrimidine for -

transversion: purine for - and vice versa

transition, transversion

purine, pyrimidine

pyrimidine

transversion mutations are - (less/more) common than transition mutations because it is sterically difficult to pair - or -

less, purine with purine, pyrimidine with pyrimidine

depurination is when purines lose their base to form - sites

depyrimidination is when pyrimidines lose their base to form - sites

apurinic

apyrimidinic

mutagens are any agent that - DNA, alters its -, or interferes with its function can induce a -

damages, chemistry, mutation

chemical mutagens are classified by mode of action (three things)

• base analogues

• DNA modifying agents

  • intercalating agents

physical mutagens include -

UV light

base analogs are chemicals that can substitute for -

example: - pairs with both A and G leading to -

nucleotide bases

5-BU, mutations

applications for base analogs (three)

• BrdU labelling used to detect -

• FACS

• labelling -

cell proliferation, DNA/RNA

DNA-modifying agents change structure of - and therefore alter -specificity

example: MNNG is an alkylating agent that methylates -, causing it to base pair with -

base, base-pairing

G, T

intercalating agents insert into - causing distortion in the structure interfering with - introducing -

DNA, replication, mutations

UV radiation causes formation of - bonds between -

results in - → replication - → DNA can’t act as template

covalent, adjacent pyrimidines

thymine dimers, inhibition

wild type is the - form of gene

most prevalent

forward mutation is a mutation from - to - phenotype

wild, mutant

reversion mutation is a second mutation at the - (different/same) site that restores - phenotype

same, wild type

suppressor mutation is when - phenotype is restored by mutation at a - (different/same) site than original site

wild-type, different

Silent forward mutation: change in NT - (does/doesn’t) change the AA due to -

doesn’t, degeneracy

missense forward mutation: change in NT results in - (same/different) AA

different

conservative/neutral forward mutation: when AA change substitutes an AA with - (similar/different) properties

similar

nonsense forward mutation: converts sense codon to - codon

results in early - of translation and a - polypeptide

stop/nonsense

termination, shortened

frameshift forward mutation: insertion/deletion of one or two base pairs changes -, usually -

reading frame, deleterious

reversion mutation are any mutational process or mutation that restores - genotype to cells already carrying a phenotype-altering forward mutation

true reversions restore the wild-type -

pseudoreversions restore the wild-type - by a compensating gene sequence change

wild-type

gene sequence

phenotype

intragenic suppressor mutations restores - phenotype via a second mutation in the - (same/different) gene

wild-type, same

extragenic/intragenic suppressor mutations restores - phenotype via a second mutation -

wild-type, elsewhere

lethal mutations results in -

death

conditional mutations are only expressed under certain -

masked under - set of conditions and visible under - set of conditions

environmental conditions

permissive, restrictive

auxotrophic mutant results in inactivation of - → unable to make -

auxotrophic mutants have conditional phenotypes because if given correct -, pathway may -

biosynthetic pathway, essential macromolecules

intermediates, continue

wild-type strain that gave rise to auxotrophic mutant is called -

prototroph

resistance mutant has acquired - to some - or -

resistance, pathogen, chemical

regulatory sequences are responsible for controlling -

gene expression

mutations in operator site produce altered operator sequences not recognized by - → operon is always -

repressor, transcribed

Why are mutations important for organisms (microbes)?

Can enhance - during - environmental conditions

survival, changing

Why are mutations for important for microbial geneticists?

• Mutant strains are used to study - (such as DNA replication, flagellar rotation, etc.)

• use of - in recombinant DNA procedures

complex processes

selective markers

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