RNA Transcription and Processing Flashcards
what is basic overview of gene expression?
which step is the most important?
DNA —–(1)——> RNA -—–(2)—–> Protein
1 = transcription
2 = translation
most important: synthesis of mRNA from the gene / transcription
where does transcription and translation occur?
transcription: nucleus
translation: cytoplasm
- what acts as template for RNA synthesis?
- DNA acts as a template for RNA synthesis in the nucleus
what regulates DNA regulation / why? *come back and edit*
temporal and spatial controls of DNA replication -> get multiple control points in the process
e.g. transcriptional control
which enzymes synthesiss RNA?
RNA and DNA are synthesised in which directions?
which DNA stand can be used as template for RNA synthesis?
- RNA polymerases
- RNA is synthesised in 5’-3’ direction only (DNA synthesised in both directions)
- DNA template is therefore read in 3’-5’ direction
what does RNA polymerase I do?
what does RNA polymerase II do?
(- RNA polymerase 1: makes rRNA -> structural and catalytic subunits of ribosomes)
- polymerase II makes (among other things) mRNA - code for proteins
what are the 5 steps in mRNA synthesis?
- initiaition - RNA polymerase binds to the gene
2. Elongation: (of mRNA). the RNA polymerase transcribes the gene
3. termination: RNA polymerase stops transcribing the gene
4. processing: pre mRNA -> mature mRNA is formed
5. export: mRNA leaves nucleu
which DNA stand is used as a template for transcription / which isnt? why?
what are the strands called?
- only one of the 2 DNA strands is transcribed. only the 3’ - 5’ ->called the antisense or template strand. means we get correct 5’ - 3’ direction
- the sense strand / non template stand has same sequence as the RNA -> also called the coding strand
describe how initiation of transcription works
- DNA unwinds close to a gene, RNA polymerase binds to a promoter sequence: how?:
- the promoter sequence acts as a template for the assembly of the multi component complex of proteins, called the pre-initiation complex, which brings pol II to gene
- once bound, the RNA polymerase II can then start trancribing the gene. (get transcription intition, elongation and termination)
- transcription always starts at ATG on Exon 1
name some upstream features of transcriptional start site that are important
proximal promoter region:
- TATA box: allows RNA polymerase II to orientate correct position on the gene.
- upstream and downstream elements (from the start site ) that have a positive and negavively effect the rate of transcription in a gene.
what determines the rate of transcription of gene?
how do transcription factors interact with RNA polymerase II?
- rate of assembly of complex (of transcription factors): determines the rate of transcription of the gene.
- transcription factors interact with the RNA polymerase II and general transcription factors either directly or via bridginf proteins co-factors. its complex!
explain elongation of RNA synthesis
Elongation:
- RNA polymerase synthesises complementary RNA in the 5’ - 3’ direction. uses NTP (ribonucleoside triphosphates)
- ’ DNA is transcribed from the antisense / template strand
what are the differences between the structure of RNA and DNA?
differences:
DNA: 2’C on sugar ring: H
RNA: 2’C on sugar ring: OH
what connects different nucleotide units?
phosphodiester bonds
what processes are involved to ensure that primary mRNA is modified before the export into cytoplasm?
- capping: at 5’ end.
- splicing: introns are cut out of RNA transcript
- poly adenine tail: lots of A added at 3’ end to make a poly A tail
how does capping occur?
as the first nucleotide is transcribed, cap is added onto the 5’ prime end. cap made from:
7-methly guanoside and triphosphate linkage (added onto the first transcribed nucleotide)
explain how RNA splicing works
what is alternative splicing of mRNA? what does it result in?
INTRONS (non-coding RNA) are spliced out of pre mRNA. leaving the EXONS in mature RNA
alternative splicing: alternative exons might or might not be included, and there may be exon skipping, intron retention, alternative 5′ and 3′ splice sites and mutually exclusive exons [7] , leading to the generation of potentially hundreds of proteins from a single mRNA. get different isoforms of proteins. (baso different
explain RNA termination
- RNA polymersae reaches terminator sequence, transcription stops.
- poly-A tail added on
- transcript is cleaved
describe structure of mature RNA have
- 5’ cap.
- 3’ poly A tail
- only coding sequences on
how is mRNA exported into cytoplasm?
through nuclear pores (via complex of proteins) into cytoplasm
infer the mRNA sequence from this DNA sequence
what can mutations within transcription factors lead to ?
loss of function of nucleosome remodelling (its in wrong shape) can lead to?
- fibroids, prostate cancer and developmental disorders
- nucleosome remodelling: cancers
what is a transcription factor that is amplified going to do?
give example of this
= get lots of TF. switches on more genes for longer. if that gene codes for growth protein -> lead to cancer. (therefore theyre an oncogene)
- e.g. cMYC-one is most commonly amplified oncogene
AIRE-gene defects leads to autoimmune disorders
what can misregulating of splicing cause?
a) due to mutated splice sites
b) mutate splice machinery
- *mutated splice sites:**
- cancer (BRAC1 and 2)
- Frasier syndrome
- spinal muscular atrophy (SMN2)
- atypical CF (CFTR)
mutated splicing machinery:
- retinitis pigmentosa
- spinal muscular atrophy (
- myotonic dystrophy
