Lecture 2 - Genetic Variation

Question 1

Define heterozygosity

Answer 1

2 copies of genes to minimise loss of function due to mutations still have one functional copy and we can survive off this

Question 2

Define apoptosis

Answer 2

Damaged cells killed to prevent transmission of mutated genes and it is not passed onto daughter cells

Question 3

Define cell cycle control

Answer 3

Checkpoints during cell division to ensure the cell is healthy to damaged DNA that could be passed onto daughter cells - could lead to excess cell proliferation

Question 4

What is the role of tumour suppressor genes?

Answer 4

ACT as a break on cell growth
Push cell towards apoptosis and death
Stop the cell cycle and repair the DNA prevent it being passed onto daughter cells

Question 5

Define translocations

Answer 5

Aberrant crossovers between chromosomes during cell division
Can lead to genes normally regulated by one promoter becoming separated from this and being controlled by another
Can dys-regulate gene expression and may lead to alterations in cell growth and susceptibility to death

Question 6

Give an example of a translocation

Answer 6

Bcl-2 - has been translocated to come under control of the ig promoter (gene expression)
Bcl-2 is over expressed in these cells => reduced ability to die by apoptosis

Question 7

How do mutations occur?

Answer 7

environmental factors
inherited factors
viral factors

Question 8

How do insertions/ deletions of nucleotide bases affect protein function?

Answer 8

Might scramble the encoded mRNA - loss of functional protein due to different amino acids and proteins (non-sense proteins)

Question 9

What are single base mutations?

Answer 9

Can lead to single amino acid difference in the altered protein which could lead to a change in functional activity

Question 10

Define oncogenes

Answer 10

Mutated forms of normal cellular genes which control cell growth
usually dominant
usually encode for GF, receptors, signal transducers or nuclear transcription factors

Question 11

Describe the role of p53

Answer 11

Unstable, degraded if it approaches damaged DNA
Allows the cell cycle to be paused and the damaged DNA fixed and prevents it being passed onto daughter cells

Question 12

What does the loss of p53 function lead to?

Answer 12

cancer
cant induce cell death
pass damaged DNA onto daughter cells eventually leading to a tumour

Question 13

How does lung cancer occur?

Answer 13

Mutagen causes G>T transversions in DNA - mutations lie within the DNA binding regions

Question 14

Describe the inherited mutation of CF?

Answer 14

3 nucleotide deletion of phenylamine - incorrect folding and therefore degradation before its expressed in the membrane therefore there is no chloride channels in the membrane

Question 15

Describe the inherited mutation in sickle cell anameia

Answer 15

A>T
glutamic acid substituted by valine
hydrophobic amino acid - doesn’t bond well in aqueous solution so the haemoglobin and valine molecules clump together leading to distortion to the red blood cell decreasing its ability to carry oxygen around the body

Question 16

Describe the inherited mutation in X-SCID

Answer 16

Mutation in cytokine receptor signalling chain
WBCs cant function properly so we get immune deficiency

Question 17

Define ECF

Answer 17

Growth factor
drives cell proliferation
intrinsic kinase domain leading to activation of Ras/MAPK

Question 18

Define ligand independence

Answer 18

Doesnt require GF anymore sits in the membrane and is always signalling

Question 19

Define overexpression

Answer 19

gene amplification - copying DNA and slips on the template and copies the gene again, 2 copies of gene