Topic 8—A:Mutations and Gene Expression-1. Mutations

Question 1

What are mutations?

Answer 1

• Any change to the base (nucleotide) sequence of DNA

Question 2

How can mutations be caused?

Answer 2

• By errors during DNA replication

Question 3

How can the rate of mutations be increased?

Answer 3

• by mutagenic agents

Question 4

What are the different types of mutations?

Answer 4

• substitution
• deletion
• addition
• duplication
• inversion
• translocation

Question 5

Substitution

Answer 5

• one or more bases are swapped for another
  E.g. ATGCCT
  —
  becomes ATTCCT
  —
  (G is swapped for T)

Question 6

Deletion

Answer 6

• one or more bases are removed
  E.g. ATGCCT
  —
  becomes ATCCT
  (G is removed)

Question 7

Addition

Answer 7

• one or more bases are added
  E.g. ATGCCT

becomes ATGACCT
—

(A is added)

Question 8

Duplication

Answer 8

• one or more bases are repeated
  E.g. ATGCCT becomes ATGCCCCT
  —
  (CC is repeated)

Question 9

Inversion

Answer 9

• a sequence of bases is reversed
  E.g. ATGCCT
  ——
  becomes ATCCGT
  ——
  (GCC is reversed to CCG)

Question 10

Translocation

Answer 10

• a sequence of bases is moved from one location in the genome to another
• this could be movement within the same chromosome or movement to a different chromosome

Question 11

What determines the sequence of amino acids in a particular polypeptide?

Answer 11

• order of DNA bases in a gene

Question 12

What happens to the sequence of amino acids in the polypeptide if a mutation occurs in a gene?

Answer 12

• they could be changed

Question 13

What do polypeptides make up?

Answer 13

• proteins

Question 14

What may change as a result of a change in the amino acid sequence of a polypeptide?

Answer 14

• It may change the tertiary structure (final 3D shape) of the protein which could mean that it doesn’t work properly
  E.g.
  a mutation in a polypeptide that makes up an enzyme may change the shape of the enzymes active site
  This may stop substrates from being able to bind to the active site leaving the enzyme unable to catalyse the reaction

Question 15

What can some mutations increase the likelihood of?

Answer 15

• developing certain cancers
  E.g. mutations of the gene BRCA1 can increase the chances of developing breast cancer

Question 16

What can some mutations cause?

Answer 16

• genetic disorders

Question 17

What are genetic disorders?

Answer 17

• inherited disorders caused by abnormal genes or chromosomes
  E.g. cystic fibrosis

Question 18

What will happen to the mutation Of a gamete (sex cell) containing a mutation for a type of cancer or a genetic disorder is fertilised?

Answer 18

• the mutation will be present in the new fetus formed- these are called hereditary mutations because they are passed on to offspring

Question 19

What does the degenerate nature of the genetic code mean?

Answer 19

• some amino acids are coded for by more than one DNA triplet
• this means that not all types of mutation will always result in a change to the amino acid sequence of the polypeptide

Question 20

Definition of frame shift mutation

Answer 20

• a mutation that changes the number of bases in the DNA code, causing a shift in the base triplets that follow, so that the triplet code is read in a different way