Transcription Flashcards
RNA: general features
- ribonucleic acid
- Uracil replaces Thymine
- single stranded (folds into itself)
- less stable than DNA
central dogma:
- flow of information:
- transcription
- translation
- protein
hypotheses on one gene one ?
- 1 gene 1 enzyme
- 1 gene 1 protein
- 1 gene 1 polypeptide
- not correct (alternative splicing)
transcription:
- synthesis of RNA using DNA
- similar to DNA replication
- uses DNA as template for complementary RNA strand
types of RNA and job:
mRNA:
- messenger RNA
- carries message from DNA to protein
rRNA:
- ribosomal RNA
- structural RNA which forms ribosome
tRNA:
- transfer RNA
- structural RNA involved in synthesis of amino acid chains
where does transcription occur in eukaryote and prokaryote:
prokaryote:
- no nuclei
eukaryote:
- transcription and RNA processing inside nucleus
- translation in cytoplasm
template strand:
- 1 of 2 strand of DNA
- 3’ to 5’
how does RNA synthesise to DNA template strand:
- antiparallel direction
- T replaced with U
- synthesised 5’ to 3’ direction
coding strand:
identical to RNA strand (but has T)
- non-template strand (5’ to 3’)
transcription process: overview
- RNA polymerase separate DNA double helix and adds RNA nucleotides
- RNA pol adds in 5’ to 3’ direction
- don’t need primer
- only 1 RNA pol in bacteria vs at least 3 in eukaryotes
promoter:
where RNA pol attaches and starts transcription
terminator:
in bacteria where transcription stops
upstream and downstream?
- promotor end is upstream
- terminator end is downstream
list stages of transcription:
- initiation
- elongation
- termination
initiation: prokaryote
RNA pol binds to promoter region
initiation: eukaryote
transcription factors mediate binding of RNA pol II
- TATA box needed to initate transcription
elongation: both
- RNA pol untwists double helix 10-20 nucleotides at a time
- adds to 3’ end
- in convoy, multiple RNA pol can transcribe same gene to make proteins quickly
adds 40 nucleotides/ sec in eukaryotes
termination: both
bacteria:
- transcribed terminator signal causes RNA pol to detach
eukaryotes:
- polydenylation signal AAUAAA signals proteins to bind RNA molecule, cut it, release RNA pol from RNA transcript
- proteins cleave off RNA pol II
RNA processing contd:
- pre-mRNA is produced in eukaryotes
- occurs in nucleus
- 5’ cap added and (50-250 As) are added to 3’ end to form poly A tail
purpose of poly A tail and 5’ cap
- help export mRNA out of nucleus into cytoplasm
- protect mRNA from degradation
- help ribosomes attach to 5’ end of mRNA
mRNA splicing:
- non coding regions are removed
- exons spliced together
- spliceosome cuts out introns
- mature RNA moves into cytoplasm
universal information flow:
almost universal flow of information from bacteria to eukaryotes
- supports common ancestry
- biotech: eg. insulin from humans into bacteria to mass produce
alternative mRNA splicing
when introns are cut out and different sections are spliced together to form proteins
