Gene expression

Question 1

central dogma of molecular biology

Answer 1

DNA -> RNA -> protein
RNA -> DNA retroviruses
not all RNA becomes a protein - tRNA, rRNA, miR

Question 2

DNA definition

Answer 2

a long molecule made up of a string of deoxyribonucleic acids - the sequence contains information to generate a new organism

Question 3

Genome definition

Answer 3

sequence of all the DNA in an organism (genes + non-coding regions)

Question 4

gene definition

Answer 4

unit of inheritance (many code for proteins, but not all)

Question 5

5’ UTR

Answer 5

CAP addition site

Question 6

START

Answer 6

ATG

Question 7

introns

Answer 7

non-coding DNA

Question 8

exons

Answer 8

coding DNA

Question 9

STOP

Answer 9

e.g. TAA

Question 10

3’ UTR

Answer 10

PolyA addition site

Question 11

process of transcription

Answer 11

initiation, elongation, termination

Question 12

Initiation

Answer 12

RNA polymerase II to the start of the gene, DNA strands pull apart

Question 13

Elongation

Answer 13

RNA gets longer (forms a transcription bubble)

Question 14

Termination

Answer 14

RNA synthesis

Question 15

processing in nucleus

Answer 15

5’ CAP
3’ PolyA tail
splicing by spliceosome (removal of introns)
now it mRNA

Question 16

what are transcription factors

Answer 16

proteins
bind to short but very specific sequences of DNA
affect rate of transcription (positively or negatively)
- turns genes ‘on’ or ‘off’
- ‘activators’ or ‘repressors’ respectively
master regulators
mutation TFs and TF-binding site underline many diseases

Question 17

examples of TFs

Answer 17

p53 and E2F in control of cell cycle
nuclear hormone receptors -> ligand-dependant TFs
- glucocorticoid receptor
- oestrogen receptor
- testosterone receptor
- retinoic acid receptor
steroid act on TFs

Question 18

transcription initiation complex (TIC)

Answer 18

RNA polymerase II cannot bind directly to DNA
general or basal transcription factors acts as a bridge

Question 19

mutations in TATA box of B-globin (HBB) gene promotor

Answer 19

THALASSAEMIA (SEVERE ANAEMIA)

Question 20

mutation in CCR5 promotor

Answer 20

AFFECTS RATE THAT HIV PROGRESSES TO AIDS

Question 21

mutations in factor IX promotor

Answer 21

HAEMOPHILIA B

Question 22

mutations in LDLR promotor

Answer 22

FAMILIAL HYPERCHOLESTEROLEMIA

Question 23

enhancers and silencers

Answer 23

DNA sequences where transcription factors bind to affect rate of transcription
can be upstream or downstream of a gene
can be close or very far away
makes it more likely (enhancer) or less likely (silencer) that a promotor is activated
are required for expression of most genes

Question 24

examples of enhancers and silencers

Answer 24

p53 - activator of transcription of p21 -> cell cycle arrent and DNA repair
- repression of transcription of surviving -> apoptosis
E2F - activator of transcription of genes needed for S phase (Lamins etc)
Oct-1 - repressor of transcription of TSH (thyroid stimulation hormone) in all cells apart from thyrotropes in the pituitary
Snail - repressor of E-cadherin in epithelial cancers -> less cell-cell adhesion, more invasive ability

Question 25

single nucleotide polymorphisms (SNP)

Answer 25

mutations frequently found in enhancers or silencers

Question 26

nucleosomes

Answer 26

keep DNA ‘closed’
DNA is not always accessible to TFs

Question 27

locus control regions

Answer 27

open chromatin spanning several genes
example: globin genes
- transcription factors bind to globin LCR (only in erythrocytes)
- opens DNA of all globin genes
- gene expression possible

Question 28

clinical significance -> mutations in LCR

Answer 28

locus stays closed, globin expression very low
Hispanic (GDB) Thalassaemia
no mutations in the globin genes, it is amount made which is affected