1.3.6 - Gene mutation

Question 1

what is a mutation?

Answer 1

a permanent change in the DNA of an organism
(could be due to a codon being changed/misread, –> amino acid it codes for is different –> polypeptide chain is altered)

Question 2

what are point or gene mutations?

Answer 2

a change in one or a small number of nucleotides affecting a single gene

Question 3

what are the 3 types of gene mutations?

Answer 3

substitutions
deletions
insertions

Question 4

what are substitution mutations?

Answer 4

type of point mutation in which one base in a gene is substituted for another

Question 5

what are deletion mutations?

Answer 5

type of point mutation in which a base is completely lost

Question 6

what are insertion mutations?

Answer 6

type of point mutation is which an extra base is added into a gene, which may be a repeat or a different base

Question 7

what are chromosomal mutations?

Answer 7

changes in the position of entire genes within a chromosome

Question 8

what are whole- chromosome mutations?

Answer 8

the loss or duplication of a whole chromosome

- e.g Down’s syndrome (caused by whole-chromosome mutation at chromosome 21)

Question 9

how can mutations be fatal?

Answer 9

base change in protein that plays an important role in the cell (e.g active site of an enzyme) –> effect is catastrophic
- also mutations in the wrong place can disrupt the biochemistry of the entire organism

Question 10

what is sickle cell disease?

Answer 10

(sickle cell anaemia)

• a human genetic disease affecting the protein chains making up the haemoglobin in the red blood cells
• result of point mutation
• RBC can’t carry oxygen efficiently + block the smallest blood vessels
• single change in one nucleotide –> causes severe pain and even death

Question 11

how can a change in one nucleotide affect the structure and function of the protein formed and hence the phenotype of an individual in a deletion mutation?

Answer 11

• base is lost
• all other bases move up
• all the codons in the mRNA are different
• all the amino acids are different
• polypeptide fold to form a different shape
• enzyme can’t function as the shape of the active site has changed
• individual = not healthy

Question 12

how can a change in one nucleotide affect the structure and function of the protein formed and hence the phenotype of an individual in a substitution mutation?

Answer 12

• one base is substituted
• one triplet is different
• one codon is different
• one amino acid is different
• polypeptide forms a different shape
• the enzyme can’t function because the shape of the active site has changed
• individual = not healthy

Question 13

what is a mutagen?

Answer 13

anything that increases the rate of mutation

• e.g x-rays, ionising radiation, certain chemicals
• better to keep exposure of these mutagens to a minimum