Mutations lectures (2)

Question 1

why are bacteria good model systems?

Answer 1

• unicellular (change in phenotype WILL affect that cell)
• single chromosome - haploid - no competing alleles
• replicate by binary fission
• > all daughter cells identical to parent
• > no genetic variation
• simple gene structure

Question 2

Stop codons

Answer 2

UAA, UAG, UGA

Question 3

mutants in bacteria

auxotrophs

Answer 3

amino acid/vitamin

Question 4

mutations in bacteria

resistance

Answer 4

antibiotics/phage/toxic chemicals

Question 5

mutations in bacteria

inability to use a substrate

Answer 5

sugar

Question 6

non-selective media

Answer 6

all cells grow so test individual colonies

Question 7

selective media

Answer 7

e.g. antibiotic present / absence of amino acid

Question 8

indicator media

Answer 8

e. g. MacConkey Agar

- identifies whether bacteria use lactose

Question 9

silent mutation

Answer 9

different codon, same amino acid

Question 10

missense mutation

Answer 10

different amino acid, different protein

Question 11

nonsense mutation

Answer 11

changes to stop codon, cuts protein short

Question 12

frame-shift mutation

Answer 12

adds/removes nucleotide, shifts sequence

Question 13

deletions

Answer 13

removes genes, may change phenotype

Question 14

insertions

Answer 14

adds gene(s), may change phenotype

Question 15

rearrangements

Answer 15

reorders gene (s), may not change phenotype

Question 16

point mutations

Answer 16

affect one single gene

Question 17

types of point mutations

Answer 17

• silent mutations
• missense mutations
• nonsense mutations
• frame-shift mutations

Question 18

types of larger-scale mutations

Answer 18

• deletions
• insertions
• rearrangements

Question 19

reverse and suppressor mutation types

Answer 19

• forward mutation

- reversion

Question 20

what is a forward mutation?

Answer 20

wild type sequence -> mutant sequence

Question 21

what is a reversion mutation?

Answer 21

1) reverse
mutant sequence -> wild type sequence

2) suppressor
mutant sequence

Question 22

Types of reversion mutation

Answer 22

• reverse

- suppressor

Question 23

Mutation Rate formula

Answer 23

= ratio in a population of (number of mutants/number of wild types)

Question 24

requirements for measuring frequency of mutation

Answer 24

large populations

special techniques

Question 25

Induced mutations are caused by…

Answer 25

mutagens and radiation

Question 26

transition mutations

Answer 26

pyrimidine -> pyrimidine

purine -> purine

Question 27

transversion mutations

Answer 27

pyrimidine -> purine

purine -> pyrimidine

Question 28

why are transition mutations more common than transversion mutations?

Answer 28

pyrimidines and purines (two rings) are more structurally different from each other than within their group.

Question 29

Spontaneous mutations

Answer 29

independent of selective (dis) advantage to host
each gene mutates at a characteristic rate
each type of mutation occurs at a characteristic rate

Question 30

Base Analogues

Answer 30

molecule similar to one of the four DNA bases

Question 31

Base analogues incorporated into DNA…

Answer 31

ONLY at replication

Question 32

Base analogues can…

Answer 32

pair with a normal base

Question 33

Example of a base analogue to thymine

Answer 33

5 - bromouracil

Question 34

nitrous acids causes what type of mutations?

Answer 34

transitions A-T -> G-C

Question 35

alkylating agents cause what type of mutations?

Answer 35

transition A-T -> G-C

Question 36

Intercollating chemicals

Answer 36

planar, ringed molecules the size of a base pair (bp)

Question 37

examples of intercollating chemicals

Answer 37

acridine

ethidium bromide

Question 38

order these mutations in their ease to be fixed and tolerance to mutation by radiation

• ssDNA breaks
• nucleotide substitution
• dsDNA breaks

Answer 38

• nucleotide substitution
• ssDNA breaks
• dsDNA breaks

Question 39

DNA repair mechanisms

Answer 39

Apurine gap repair
Mismatch pair 
Photoreactivation repair 
Excision repair 
Post-replication repair

Question 40

Apurine gap repair

Answer 40

uses AP endonuclease
- removed damaged base
- ss gap filled by polymerase
if no repair inserts A

Question 41

Mismatch pair

Answer 41

nearby ss cut and excision of ssDNA past mismatch

DNA polymerase repairs gap

Question 42

Photoreactivation repair

Answer 42

light driven process

various enzymes with specific properties

Question 43

Excision repair

Answer 43

multi-enzyme system
enzymes identify & instant removal
polymerase repairs

Question 44

Post-replication repair

Answer 44

polymerase can't replicate across damaged DNA, leaves gap
gap filled by strand exchanged from another dsDNA
secondary gap (from where strip take - not damaged) repaired by polymerase