RNA Transcription In Eu Genes Flashcards
What are the 6 stages of regulation of eukaryotic gene expression?
1) transcription (most important regulatory step)
2) RNA processing
3) mRNA transport
4) mRNA translation
5) mRNA degradation
6) protein degradation
Steps 2-6 are dependent on transcription having taken place correctly
When is gene transcription regulated?
1) during differentiation and development (highly ordered)
2) as a response to the environment (food, hormones, toxins)
3) depending on the function of the cell (tooth cells will need different proteins to kidney cells)
What type of diseases do problems in gene transcription result in?
1) cancer: absence of T off switch leads to wrong genes being expressed and cell division.
Oncogenes and proto-oncogenes = mutated or missing:
Cells continue to divide and can’t differentiate because T has not been switched off.
So absence of an off switch can lead to cancer.
2) developmental diseases: mistakes in transcription, early in embryogenesis can lead to serious organ developmental problems.
Wilms’ tumour (kidney cancer affecting young children): caused by mutation on ch 11 (WT1 gene). It is a transcriptional regulator, so a mutation means the kidney doesn’t differentiate properly (parts keep growing)
3) chronic diseases: eg obesity.
Abnormal GE as a result of the wrong signals in the cell cause inflammation and increased risk of other disease eg cardiovascular disease
What is needed for transcription?
1) DNA template with correct signals
2) enzymes which can copy DNA into RNAs
The output of transcription is RNAs which can be used by the cell to make proteins
What are the 3 main types of RNA produced by T in Eu cells?
1) mRNA - code for proteins (3% of total RNA)
2) ribosomal rRNA - form basic structure of ribosome and catalyse PS (71%)
3) transfer tRNA - act as adaptors between mRNA and AAs (15%)
When extract RNA from human tissue, mRNA is only a small % of the total RNA in a cell, but it has a big job - to code for all cell’s proteins
What are the features of mature mRNA?
1) initiation codon: where the first AA (methionine) will be coded
2) termination codon: end of coding sequence
ORF in between 1&2 = codon triplets which code for a peptide
3) polyadenylation signal: in the 3’ UTR where here are signals - 95% of the time it’s AAUAAA
4) poly A tail: lots of adenosine nucleotides added to increase stability
- untranslated regions in both ends all copied from DNA (5’ and 3’ UTR)
What do RNA polymerases (multi-subunit enzymes) do?
Make RNA from DNA.
1) RNA pol I synthesises rRNA
2) RNA pol II synthesises mRNA
3) RNA pol III synthesises tRNA, 5S rRNA, snRNAs
- These enzymes were purified by elution at different salt concentrations
- Each has a different sensitivity to the fungal toxin a-amanitin (inhibits RNA polymerase)
- RNA pol II cannot transcribe mRNA from DNA on its own - needs many helpers
How is transcription initiated?
To transcribe a gene, a pre-T initiation complex has to assemble upstream of the start site which helps RNA polymerase II to get started
- A number of proteins come together in a specific order to help RNA pol II transcribe genes = GTFs
- GTFs position RNA pol II at promoter resulting in a PIC
- Polymerase then copies DNA into RNA
- Major regulatory point in Eu cells
What are regulatory molecules?
Regulatory molecules: trans - not on the same molecule as DNA
- proteins which control T initiation by binding to DNA
- made in cytoplasm and go back into nucleus and bind to DNA
- can diffuse through cell from site of synthesis to bind to the regulatory sequence (such as a promoter) and affect T
- usually have 2 domains, a DNA binding domain and a T activation domain
- eg GTFs needed for T initiation
What are regulatory sequences?
Cis - usually very close to the start site of the gene
- short sequences of DNA which control T initiation
- usually found in non-coding (no protein being made) regions of genome
- these regions have a high affinity to GTFs
- interact with DNA binding proteins eg. TFs resulting in induction or repression of TFs resulting in induction or repression of T initiation
- called “cis” bc they influence genes on the same DNA molecule
- eg. TATA box, HREs (hormone responsive elements)
What is the link between cis acting regulatory sequences and trans acting regulatory sequences?
1) DNA > mRNA > Protein (TAF)
2) TAF goes back into the nucleus where it binds to a different bit of DNA which regulates something (binds to CAS)
3) RNA pol II comes to copy
GTF (TAF) > Promoter eg TATA > RNA pol II > Copy
What is the TATA box?
- the most common promoter
- highly conserved (across different life forms) promoter in many Eu genes
- located ~25-35bp upstream from the start site of transcription
- involved in positioning of the RNA pol II (via GTFs) for correct T initiation (large % of gene had the TATA box motif)
How is gene expression regulated?
- expressed selectively under certain conditions/specific cells
- eg. Cyclins required for cell division expressed at a specific stage in cell cycle OR a gene expressed only in skin cells
What are promoters?
- short sequence found upstream of a coding region
- important in initiation of transcription
- site where PIC is assembled
- eg the TATA box
What are TFs?
- Proteins which ensure that genes are correctly expressed at a specific time and in response to internal or external stimuli
- Can bind specific DNA sequences and specific proteins eg promoter or RNA pol II
