WEEK 12 (Gene mutation, DNA repair and transposition)

Question 1

Single nucleotide substitutions are repaired by which DNA enzymes?

Answer 1

DNA polymerase & DNA Ligase

Question 2

What are the two types of single nucleotide (point) mutations?

Answer 2

Transition & Transversion mutations

Question 3

What is the difference between Transition and Transversion mutations?

Answer 3

Transition mutations involve PURINE TO PURINE substitutions or PYRIMIDINE TO PYRIMIDINE

Transversion mutations involve PURINE TO PYRIMIDINE or PYRIMIDINE TO PURINE

Question 4

List three types of single nucleotide substitutions

Answer 4

• Silent mutation
• Missense mutation
• Nonsense mutation

Question 5

What is a silent mutation?

Answer 5

A silent mutation codes for the same amino acid & often involves the 3rd position of the codon

Question 6

What is a missense mutation?

Answer 6

A missense mutation results in a changed amino acid (called CONSERVATIVE if new amino acid has similar chemical structure)

Question 7

What is a nonsense mutation?

Answer 7

A nonsense mutation results in an early STOP codon (UGA, UAA, UAG) & usually generates a nonfunctional protein

Question 8

What are the three stop codons?

Answer 8

UGA, UAA & UAG

Question 9

What is the start codon?

Answer 9

Methionine

Question 10

What is a Frameshift mutation?

Answer 10

Deletion or insertion of any number of nucleotides not divisible by 3 resulting in the misreading of all nucleotides downstream. Protein may be shorter or longer and its function may be disrupted or altered.

Question 11

What is a Splice site mutation?

Answer 11

Retained intron remains in mRNA resulting in proteins with impaired or altered function

Question 12

What is a loss-of-function mutation?

Answer 12

A mutation that reduces or eliminates the function of the gene product

Question 13

Define Null mutations

Answer 13

Mutations that result in complete loss of function

Question 14

What is a recessive mutation?

Answer 14

Results in a wild-type phenotype when present in a diploid organism and the other allele is wild type

Question 15

What is a dominant mutation?

Answer 15

Results in a mutant phenotype in a diploid organism, even when the wild-type allele is also present

Question 16

What happens in a Dominant negative mutation?

Answer 16

One allele may encode a gene product that is inactive and directly interferes with the function of the product of the wild-type allele

Question 17

What is a Gain-of-function mutation?

Answer 17

Codes for a gene product with enhanced, negative or new functions

Question 18

What is a suppressor mutation?

Answer 18

A second mutation that either reverts or relieves the effects of a previous mutation. A suppressor mutation can occur within the same gene that suffered the first mutation (INTRAGENIC MUTATION) or elsewhere in the genome (INTERGENIC MUTATION).

Question 19

What is a nucleosome?

Answer 19

A repeating unit of chromatin

Question 20

Histone proteins usually have a high proportion of ____________ amino acids

Answer 20

positively charged

Question 21

The probability of a particular type of mutation per unit time is known as ____________________

Answer 21

Mutation rate