Transcription & Translation Flashcards
pre transcription factors on gene expression
Transcription stages
same as replication:
Initiation: RNA polymerase binds to promoter, &opens helix
Polymerisation (Elongation): polymerase bring free nucleotides to synthesise new mRNA strand using complementary base pairing off of template strand (antisense) = copy of coding strand => chain elongation
Termination: RNA polymerase detaches at termination region, polymerisation stops, end of RNA strand folds over on itself to make hairpin loop = easier to detach (‘displace’) from DNA strand.
once displaced, DNA strand reassociates with sigma factor or transcription factors to repeat process
promoter (region) vs start codon
promoter (region):
- sequence of bases/nucleotides where polymerase binds to start transcription (upstream (5 end) of transcription)
start codon:
- first codon (bases) to be translated on mRNA strand
how are start sites found
prokaryotes: by binding of singular stigma factor
eukaryotes: by binding of multiple general transcription factors
operon
for Prokaryotes:
set of genes grouped together when being transcribed = all OPERate under same transcription factors
one promoter per operon, therefore along DNA, multiple promoters/ start sites = complete transcription (simple)
gene pathway
group of genes to make one eventual protein/ structure
how does eukaryotic transcription differ from prokaryotic
Eukaryotes have:
- genes within same pathway are often distributed over different chromosomes
- eukaryotic genes are packaged into nucleosomes / higher-order arrangements (secondary, tertiary, quaternary structures)
- 3 RNA polymerases, not 1, Polymerase II is responsible for transcription
- more complex gene processing - pre/post modification
General transcription factors in the pre-initiation complex PIC
DEFINITIONS~
(start sites in transcription)
- TFII (TF2) = transcription factor for RNA Polymerase II
TFII A, B, D, E, F, H + Polymerase II = form a large complex binding to area in the promoter region = ‘pre-initiation complex’ - Helicases (TFII H), ATPases = opening + unwinding DNA
role of TFII in pre-initiation complex
- TFII D binds to TATA box (repeating TA nucleotide sequence in promoter region)
- TFII A + B bind to D = recruits RNA Pol. II to DNA strand
- TFII E + F opens double stranded DNA (helicase, ATPase)
- TFII H stabilises complex
falls apart once polymerisation starts, recycled to start of the gene
specific (TF) transcription factor in gene regulation TF binding site + role
TFs bind even further upstream than pre-initiation complex - beginning of promoter region = ‘enhancer’ sites/ regions
function:
- help to recruit pre-initiation proteins to bind
- 1000s of different types - aid in differentiating?
transcription modulators - upstream regulatory sites
Co-factors: modulate activity of TFs, bind to TFs - influence gene expression
Co-activators: enhance gene expression
Co-repressors: dampen effect of TF (lower gene expression)
Chromatin modifiers: work within the promoter region to either add/remove acetyl/methyl groups - influences gene accessibility, expression
Mediator (protein)
acts as a bridge to fold DNA on itself so that upstream transcription factors can directly act on PIC (pre-initiation complex)/ general transcription machinery
- useful bc upstream regulatory sites may be many bases away from general transcription machinery - may be bent within chromosome to be adjacent/ higher-order of DNA.
Cis-regulatory elements
encompassing name for all transcriptional modifiers in DNA:
- can activate/ inhibit transcription synergistically or antagonistically with one another = subtle control of expression
types:
- strong activators: e.g, TFs, chromatin opening factors, PIC
- strong/weak inhibitors (repressors): weaker influencers of initiating transcription
core promoter region
TATA box (general transcription factors binding site) + transcription start site + binding site for RNA polymerase (II)
termination sequence
nucleotide sequence at end of genes to release mRNA
