mutations

Question 1

what is a substitution mutation?

Answer 1

• gene mutation
• one nucleotide is incorrectly swapped during DNA replication for another nucleotide
• the correct nucleotide is replaced with an alternative nucleotide
• effects are small

Question 2

what is a deletion mutation?

Answer 2

• gene mutation
• a nucleotide is skipped or absent from the replicated strand
• causes frameshift
• effects can be damaging

Question 3

what is an insertion mutation?

Answer 3

• gene mutation
• an extra nucleotide is incorporated into the DNA sequence during replication

Question 4

what is a gene mutation?

Answer 4

a change in the base sequence of chromosomes in the DNA

Question 5

when are gene mutations likely to occur?

Answer 5

during S phase
DNA replication

Question 6

what factors increase/decrease the rate of mutations?

Answer 6

• mutagenic agents
  eg x rays

Question 7

what is a non sense mutation?

Answer 7

translation stops before expected

Question 8

what is a missense mutation?

Answer 8

• change to a singular amino acid
• can change the protein shape

Question 9

why do deletions/insertions have bigger effects than substitution mutations?

Answer 9

• results in a frame-shift that changes the reading of subsequent codons
• alters the entire amino acid sequence that follows the mutation
• bigger effect on primary polypeptide as amino acids are incorrectly coded for
• impact upon the way the rest of the sequence is read by the cell

Question 10

what is a point mutation?

Answer 10

changes to a single nucleotide
- either inserted, substituted or deleted

Question 11

evaluate whether a base deletion mutation has a bigger effect on polypeptide structure than a base substitution mutation

Answer 11

• sub can result in silent mutation and no change to primary structure
• sub only changes a single amino acid
• sub does not change number of amino acids whereas deletion reduces by 3
• deletions are frame shift mutation, every amino acid downstream of mutation changes
• however sub can change codon to a stop and if this occurs near the start of the sequence, impact is significant

Question 12

what is a frameshift mutation?

Answer 12

• complete change to the entire amino acid sequence of a protein after the mutation site
• because of the way the translated mRNA is read by the ribosomes
• mRNA is read in codons, groups of 3 nucleotides. If an additional 1 or 2 nucleotides are added or removed, the sequence is ‘shifted’
• translation machinery cannot know that there has been an error, and still reads the sequence in triplet codons
• the entire mRNA and resulting protein are completely different.

Question 13

what makes a mutation more likely?

Answer 13

mutagenic agents
- high energy radiation (UV)
- ionisation (X ray)
- chemicals

Question 14

why can substitution mutations be silent?

Answer 14

genetic code is degenerate