Cellular Control - Mutations

Question 1

define mutation

Answer 1

a random mistake causing a change in the structure of DNA, or the structure or number of chromosomes

Question 2

when do DNA mutations happen

Answer 2

when DNA is replicating during interphase prior to mitosis or meiosis

Question 3

what can increase the rate of mutation

Answer 3

mutagens (ionising radiation, chemicals, viruses)

Question 4

what are the types of mutation

Answer 4

• substitution
• deletion
• insertion

Question 5

define substitution

Answer 5

swapping one (or more) base for another base. this will change one triplet and therefore may change one amino acid

Question 6

what is the name of a substitution mutation that has no effect

Answer 6

silent mutation

Question 7

define deletion

Answer 7

loss of one (or more) base. causes a frame shift, so all the following base triplets are disrupted

Question 8

define insertion

Answer 8

the addition of a new base(s). also causes a frame shift, so all the following base triplets are disrupted

Question 9

what are the three possible effects of a mutation

Answer 9

• no effect/neutral/silent mutations
• harmful
• beneficial

Question 10

what are the three ways in which a mutations could have no effect

Answer 10

• mutation occurs in non-coding DNA
• single base substitutions where the same amino acid is coded for because the DNA code is degenerate
• may code for a different amino acid but one that is chemically similar to the original so does not affect tertiary structure and functionality

Question 11

what are regions of DNA that do not code for a protein called

Answer 11

introns

Question 12

what are the two kinds of harmful mutations

Answer 12

• missense
• nonsense

Question 13

what are missense mutations

Answer 13

• a mutation may change the amino acids in a protein causing it to be less effective or not function at all decreasing the chance of survival of an organism
• a single base substitution may cause a single amino acid change but this change in primary structure can change the tertiary structure of the protein

Question 14

why may a change in tertiary structure be harmful, especially for enzymes

Answer 14

active site may no longer be complementary to substrate, for example

Question 15

what are nonsense mutations

Answer 15

• mutations may cause a stop codon to be introduced partway along a gene. this would lead to a short, non-functional polypeptide
• in frame shift mutations all amino acids after the deletion or insertion are altered so the protein is unlikely to function

Question 16

what may a nonsense mutation at the start of a gene cause

Answer 16

RNA polymerase cannot bind properly, so transcription cannot take place

Question 17

what are beneficial mutations

Answer 17

very occasionally a change in an amino acid in a protein can make the protein more effective, increasing an organism’s chance of survival

Question 18

give an example of a beneficial mutation

Answer 18

antibiotic resistance in bacteria

Question 19

give the three stop codons

Answer 19

ATT, ATC, ACT

Question 20

give the start codon and the amino acid it codes for

Answer 20

TAC, methionine

Question 21

what are somatic mutations

Answer 21

not inherited but can cause ageing or cancer, they are the result of mutations in normal diploid cells

Question 22

what are germline mutations

Answer 22

due to mutation during gamete formation. this can cause genetic diseases and are passed onto the next generation

Question 23

suggest why beneficial mutations are rare

Answer 23

most mutations are silent.
mutations are random - more likely to reduce the function of a protein than improve