Mutations Pt 1

Question 1

Define Mutation

Answer 1

Any alteration to the genetic material (DNA/RNA) that produces a heritable change in the nucleotide sequence

Question 2

Name the 3 types of large scale global mutations

Answer 2

• Chromosomal aberrations
• Genome rearrangements: redistribution of genetic material between non-homologous chromosomes
• Change is chromosome number (aneuploidy): e.g. trisomy resulting in Down’s syndrome

Question 3

Name the 4 types of large scale chromodomal aberrations

Answer 3

• Deletions
• Duplications
• Insertions
• Inversions

Question 4

What is a point mutation

Answer 4

single nucleotide change
e.g. base substitution or loss/gain of a single nucleotide

Question 5

What is a deletion/insertion mutation

Answer 5

Loss or gain of bases

Question 6

What is a duplication mutation

Answer 6

A sequence is repeated

Question 7

What is an inversion mutation

Answer 7

A sequence within the DNA is inverted

Question 8

What is a translocation/transposition mutation

Answer 8

Movement of a piece of DNA from one location to another

Question 9

Which chromosomal aberrations can be large-scale changes

Answer 9

• Deletions
• Duplications
• Insertions
• Inversions

Question 10

A transition mutation is considered a type of point mutation
What is it

Answer 10

Changes a purine for a purine OR a pyrimidine for a pyrimidine

Question 11

point mutations can either be

Answer 11

• Silent (missense or nonsense) due to base substitution
• Frameshift due to alteration of the reading frame with an insertion or deletion mutation

Question 12

What is an Open Reading Frame (ORFs)

Answer 12

A section of DNA or RNA that codes for a protein

Question 13

Since 3 of the 64 codons are stop codons, on average we expect to encounter a stop codon every 20 amino acids in a random sequence
How does this help us to work out where an open reading frame is

Answer 13

A gene which has very few stop codons is likely to be the reading frame for a protein
As you would have expected to have had a stop codon

Question 14

Say you had a sequence with two AAs randomly in the middle
How could you work out if it was an insertion or a deletion

Answer 14

You could translate both sequences and look for the longest open reading frame
Or to sequence more individuals from the same or closely related species

Question 15

Depending on the mutation, point mutations can have what affect on the protein

Answer 15

• No effect (same-sense, mis-sense)
• Change of function (mis-sense, small deletions)
• Loss of function (mis-sense, nonsense and frameshift)

Question 16

Why my some mutations be more disruptive than others

Answer 16

Amino acid substitutions affecting structural features or the catalytic site are likely to have major effects on protein activity

Question 17

Bacteria and yeast are examples of haploids, whereas humans are an example of diploids
How does the show in the effect of the mutation

Answer 17

Mutations of haploids always show in the phenotype
Mutations of diploids can prevent gene product synthesis OR there is no effect and hence no mutant phenotype OR an intermediate where there is a wild type and mutant gene (1:2:1 ratio)

Question 18

What is the DNA replication error rate

Answer 18

10⁻⁹

Question 19

Knowing what the DNA replication error rate is, how likely is there a mutation in an E.coli

Answer 19

E.coli only have a genome of ~10⁶
This means only 1/1000 cells has a mutation in any base pair
Hence replication is extremely accurate due to the size of their genome

Question 20

Define Mutagen

Answer 20

A chemical or physical agent that cause damage (a lesion) to the genetic material)

Question 21

Define DNA damage

Answer 21

Chemical alteration of the DNA

Question 22

What is DNA repair

Answer 22

The removal/reversal of the damage to DNA

Question 23

What is the difference between spontaneous and induced DNA damage

Answer 23

Spontaneous: Errors during DNA replication
Induced: Mutagen, lesions and DNA damage

Question 24

What is mismatch

Answer 24

When the wrong base has been added by tRNA to replicating DNA
(e.g. G instead of A)
Then is the following subsequent round of replicating, it becomes a substitution mutation

Question 25

What is a Lesion

Answer 25

A Lesion is an alteration to the chemical structure of one of the components of DNA

Question 26

What is the difference between a nick and a chromosome break

Answer 26

Nick: break in the one phosphodiester backbone (relatively easy to repair)
Chromosome break: Break in both phosphodiester backbones

Question 27

List the categories of DNA damage

Answer 27

• Adduct (single or double stranded)
• Nick or Chromosome break
• Mismatch
• Cross-link

Question 28

What are the two ways the cell can repair DNA damage

Answer 28

• Direct repair
• DNA excision repair (damaged piece of DNA is removed, then reinstated)

Question 29

Define ‘Direct Repair’ of DNA

Answer 29

A reversal of the chemical reaction causing the lesion

Question 30

What is the name of the process which causing mispairing of G with T
How it is reversed

Answer 30

O⁶-Methylguanine
Using the enzyme methyltransferase

Question 31

Define ‘DNA excision repair’

Answer 31

Removal and resynthesis of a damaged DNA section

Question 32

Thymine dimer is an example of DNA excision
What does it involve

Answer 32

A bond between two adjcent thymines on the same DNA strand
Makes it difficult for polymerase to replicate the DNA strand