Mutation

Question 1

mutant (def.)

Answer 1

an organism in which the base sequence of DNA has been changed

Question 2

mutation (def.)

Answer 2

any heritable change in the DNA sequence

Question 3

phenotype (def.)

Answer 3

• observable properties of an organism
• mutant vs. wildtype

Question 4

genotype (def.)

Answer 4

actual sequence of the DNA of an organism

Question 5

allele (def.)

Answer 5

• different forms of the same gene
• mutant vs. wildtype

Question 6

Reversion (def.)

Answer 6

-a restoration of the original phenotype to a mutant
-due to restoration of the original sequence of the gene

Question 7

Consequences of Mutation: - mutations that alter phenotype disrupt _____

Answer 7

protein function

Question 8

Alteration of DNA/RNA/protein function - must disrupt DNA/RNA/protein sequence (ways):
1) _______
2) _________

Answer 8

-change sequence of one or more codons
-change reading frame (ORF = open reading frame)

Question 9

silent MUTATIONS vs leaky mutations

Answer 9

silent: amino acid substitution that does not affect protein structure/activity
leaky: partial disruption in a protein’s activity

Question 10

Conditional vs Non-conditional mutations

Answer 10

non- conditional: mutant phenotype expressed under all conditions
conditional: mutant phenotype only expressed under
certain conditions (ex. Temperature sensitive, Suppressor sensitive, Auxotrophic)

Question 11

point mutation change? characteristics?

Answer 11

-alteration single base pair (transitions/reversions, single/double/triple), missense/nonsense
-can be leaky, revert

Question 12

deletion mutation change? characteristics?

Answer 12

-removal of DNA
-not leaky, never revert

Question 13

insertion mutation change? characteristics?

Answer 13

-addition new DNA
-not leaky, can revert

Question 14

inversion mutation change? characteristics?

Answer 14

-inversion existing DNA
-not leaky, can revert

Question 15

frameshift mutation change? characteristics?

Answer 15

-addition or deletion not equal to multiple of 3nt
-not leaky
-can revert

Question 16

point mutation: transitions

Answer 16

Pu:Py pair -> Pu:Py pair
Py:Pu pair-> Py:Pu pair

Question 17

point mutation: transversions

Answer 17

Pu:Py pair -> Py:Pu pair
Py:Pu pair -> Pu:Py pair

Question 18

1952 Lederberg & Lederberg demonstrated direct evidence that phage T1r mutations occurred _________

Answer 18

spontaneously in E. coli before exposure to phage

Question 19

1952 Lederberg & Lederberg lab technique

Answer 19

-used replica plating
- grew colonies on non-selective medium (no T1)
- replica plate to multiple plates spread with T1 phage
- T1r colonies appeared in same positions on each of replica plates

Question 20

mutation rates (def.)

Answer 20

probability that a gene will be mutated in a single generation- also referred to as chance of mutation to a particular phenotype

Question 21

mutations rate widely variable amongst different genes: dependent upon: _______ (3)

Answer 21

• gene size
• nucleotide sequence
• number of genes that dictate phenotype

Question 22

Generation of Spont. mutations (3)

Answer 22

1) Replication errors
2) alteration of nucleotides
3) recombination

Question 23

2 types of replication errors

Answer 23

i) errors in nucleotide incorporation: incorporation of tautomeric bases during replications; causing transitions
ii) slipped strand mispairing (one strand of DNA slips during replication)

Question 24

Tautomer (def.)

Answer 24

alternative forms of bases with altered base-pairing properties

Question 25

adenine (imino form) bind ____; thymine (enol form) bind _____

Answer 25

-cytosine -guanine

Question 26

tautomeric transitions may escape repair mechanisms because: ________ (2) p

Answer 26

1) proofreading -> tautomers are correctly hydrogen-bonded 2) mismatch repair -> tautomer may later assume normal structure, could be removed by the “mismatch repair”, but only if the tautomer is found in unmethylated daughter strand

Question 27

extra base is either added (slippage of ____ strand) or deleted (slippage of _____ strand). slipping occurs in ______ sequences; causes _____ mutations

Answer 27

-daughter -template -short, repeated -frameshift

Question 28

2 Alteration of Nucleotides

Answer 28

1) deamination: about 5% of cytosines in bacterial DNA are methylated (MeC); both MeC and C are deaminated occasionally 2) oxidation: reactive forms of oxygen from metabolism(peroxide/free radicals), react with and alter DNA bases (eg. guanine -> 8-oxo-guanine pairs with adenine instead of cytosine causing GC-> TA transversions)

Question 29

deamination C-> U

Answer 29

-U can pair with A -GC -> AT transition -repaired by uracil-N-glycosylase so that this rarely happens

Question 30

deamination MeC-> T

Answer 30

-T can pair with A -GC -> AT transition -MeC:G base pairs can be hotspots for mutation

Question 31

recombination between direct repeats leads to ____

Answer 31

deletions

Question 32

recombination between inverted repeats leads to ____

Answer 32

inversions

Question 33

mutagenesis -> treatments that alter the DNA; exposure of the whole organisms or just DNA to ______

Answer 33

-mutagens

Question 34

Base-Analog Mutagens: compound similar to ______ that can be incorporated into DNA during replication; H-bonds correctly, so escapes ____. to be mutagenic, must have _____ - eg. 5-bromouracil (BU); analog of _____ (tautomeric enol form predominant that frequently pairs with ___) -causes _____ MUTATIONS -if replaces a T in keto form, can tautomerize into enol form to yield _____ -can be misincorporated in enol form to yield ______ Base analog mutagens ALWAYS induce _____

Answer 34

-one of 4 DNA bases -editing - 2 modes of H-bonding -thymine -G -TRANSITION -AT -> GC -GC -> AT -transitions

Question 35

Chemical Mutagens -alter bases already incorporated into DNA to change _____

Answer 35

-H-bonding specificity

Question 36

types of chemical mutagens

Answer 36

1) nitrous acid (C-> U) 2) hydroxylamine 3) ethylmethane sulfonate (EMS)

Question 37

Intercalating Agents (def.)

Answer 37

- planar, heterocyclic molecules with same dimensions as a Pu:Py base pair

Question 38

Intercalating Agents intercalates between _____ . During replication, _______ are inserted into DNA containing intercalating agents and generates _____ mutations. this may work by stabilizing looped out bases in _______

Answer 38

- base pairs -extra base pairs - frameshift - slipped strand mispairing during replication

Question 39

mutagenesis by mutator genes: mutations in specific genes (_____) whose products are involved in _____; leads to _________ at other genes throughout the chr. (aka _____ phenotype)

Answer 39

-mut genes -DNA repair -a high mutation frequency -mutator phenotype

Question 40

mutatator gene: mutD/dnaQ dam function

Answer 40

proofreading functionof DNA pol II; methylates DNA; directs mismatch repair to correct stand

Question 41

mutatator gene: mutH, mutL, mutS

Answer 41

mismatch repair

Question 42

isolation of mutations: screens

Answer 42

- Mutants grow on media where phenotype of the mutants can be distinguished from parent - eg. COLOR INDICATOR PLATES - eg. identification of auxotrophic mutants based on inability to grow in the absence of certain metabolites (replica plating)

Question 43

isolation of mutations: selections

Answer 43

- Mutants are identified based on their ability to grow under conditions that the parent cannot (Very Powerful) - can identify a mutant on single plate of 10^10 bacteria/phage - eg. resistance mutants (antibiotic, phage resistance) - consider a rare mutation (1/10^6)

Question 44

screens vs . selections

Answer 44

screen: 100 colonies/plaques per plate; must screen 10 000 plates selections: 10^10 bacteria/phage; select mutant off 1 plate

Question 45

isolation of mutations: enrichments

Answer 45

- procedures that enrich for mutant organisms - living, multiplying cells are killed by treatment, while non-growing mutant cells are not (eg. penicillin enrichment)

Question 46

isolation of mutations: Isolation of Conditionally Lethal Mutations

Answer 46

REPLICA PLATING - mutants plated under permissive conditions --> selected under nonpermissive conditions (e.g. Host mutants)