Gene expression Flashcards
central dogma of molecular biology
DNA -> RNA -> protein
RNA -> DNA retroviruses
not all RNA becomes a protein - tRNA, rRNA, miR
DNA definition
a long molecule made up of a string of deoxyribonucleic acids - the sequence contains information to generate a new organism
Genome definition
sequence of all the DNA in an organism (genes + non-coding regions)
gene definition
unit of inheritance (many code for proteins, but not all)
5’ UTR
CAP addition site
START
ATG
introns
non-coding DNA
exons
coding DNA
STOP
e.g. TAA
3’ UTR
PolyA addition site
process of transcription
initiation, elongation, termination
Initiation
RNA polymerase II to the start of the gene, DNA strands pull apart
Elongation
RNA gets longer (forms a transcription bubble)
Termination
RNA synthesis
processing in nucleus
5’ CAP
3’ PolyA tail
splicing by spliceosome (removal of introns)
now it mRNA
what are transcription factors
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
examples of TFs
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
transcription initiation complex (TIC)
RNA polymerase II cannot bind directly to DNA
general or basal transcription factors acts as a bridge
mutations in TATA box of B-globin (HBB) gene promotor
THALASSAEMIA (SEVERE ANAEMIA)
mutation in CCR5 promotor
AFFECTS RATE THAT HIV PROGRESSES TO AIDS
mutations in factor IX promotor
HAEMOPHILIA B
mutations in LDLR promotor
FAMILIAL HYPERCHOLESTEROLEMIA
enhancers and silencers
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
examples of enhancers and silencers
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
single nucleotide polymorphisms (SNP)
mutations frequently found in enhancers or silencers
nucleosomes
keep DNA ‘closed’
DNA is not always accessible to TFs
locus control regions
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
clinical significance -> mutations in LCR
locus stays closed, globin expression very low
Hispanic (GDB) Thalassaemia
no mutations in the globin genes, it is amount made which is affected
