Mod9 - Effects of DNA Mutations

Question 1

What is the difference between a transition and a transversion mutation?

Answer 1

Transition: purine -> purine (or pyrimidine -> pyrimidine)
Transversion: purine <-> pyrimidine

Question 2

Define a nonsense mutation

Answer 2

A codon for an amino acid is changed to a stop codon

Question 3

Define a readthrough mutation

Answer 3

A stop codon is changed to a codon for an amino acid

Question 4

What is the difference between a back mutation and a second site reversion?

Answer 4

In a back mutation, the original genotype is restored, whereas in second site reversion, the second mutation does not reverse the first one, but does restore the amino acid sequence that is encoded

Question 5

What type of mutation is the delta-F508, and what effect does it have on the CFTR protein?

Answer 5

Deletion of 3 nucleotides, removing a phenylalanine codon.
The CFTR protein is still made, but does not reach the cell membrane

Question 6

What type of mutation is the G542X, and what effect does it have on the CFTR protein?

Answer 6

It is a nonsense mutation - changes a Glycine to a stop codon
CFTR protein is not made (mRNA is degraded)

Question 7

What type of mutation is the G551D, and what effect does it have on the CFTR protein?

Answer 7

It is a missense mutation - changes a Glycine to an Aspartic Acid
CFTR protein is made and reaches the cell membrane, but only works at 4% of normal rate

Question 8

What do the two components of Orkambi do to treat patients with the F508del mutation?

Answer 8

Lumacaftor - improves the conformational stability of the F508de-CFTR protein, increasing the processing and transport of the protein to the cell membrane

Ivacaftor - facilitates increased Cl- ion transport by potentiating the channel-open probability of the CFTR protein at the cell membrane

Question 9

Describe the impact on pea phenotype of having two non-functional copies of the SBE1 gene

Answer 9

Less conversion of sucrose into starch by starch synthases
-> higher sucrose
-> mature pea loses water and becomes wrinkled

Question 10

Alagille Syndrome is an example of what genetic phenomenon (and what does this mean)?

Answer 10

Haploinsufficiency - a mutation in just one copy of the gene will cause disease as not enough functional product is formed

Question 11

Retinoblastoma (familial vs sporadic) is an example of what phenomenon?

Answer 11

Carrier predisposition

Question 12

How does the Philadelphia chromosome impact cell division?

Answer 12

The control region of the abl gene has been lost, so the gene is always switched on and cell division is uncontrolled