Transcription Flashcards
stages of initiation of transcription
RNA polymerase II complex binds to promoter and opens DNA double helix
what binds to start site in eukaryotes vs prokaryotes
general transcription factors vs sigma factor
what is the TATA box
short sequence of T and A nucleotides in the promoter region where general transcription factors bind
recruits protein complex
which strand is used as the template strand
antisense
TFII
general transcription factor that recruits RNA polymerase II
elongation- compared to DNA replication
can be synthesised de novo (no primers needed)
5’-3’
true or false: many RNA molecules can be synthesised from the same gene
true
feather like structure seen with short transcripts extending from 5’ end of gene and long transcripts from 3’ end
what is transcriptional stress
DNA damage induced by breaks during transcription
can be relieved by topoisomerases
how is transcription terminated
termination signal-not same as stop codons (translation)
RNA folds into hairpin secondary structure to aid displacement from DNA
3 stages of mRNA processing
capping
polyadenylation
splicing
modification of guanine nucleotide that makes the 5’ cap
methyl group added
3’ UTR role
mRNA is cleaved after polyA signal in 3’ UTR and polyA tail added
done by polyA complex
function of polyA tail
protects mRNA from degradation
exportation from nucleus to cytoplasm
what is the spliceosome made of
complex of proteins and snRNPs and snRNA
what are snRNPs
small nuclear ribonucleoproteins
what is a ribonucleoprotein
complex of protein and RNA
snRNA
small nuclear RNA
recognise splice sites
catalyse splicing reaction
ribozymes
complex secondary structure
alternative splicing
splice variant proteins (isoforms) can have different functions in tissues
cis regulatory elements
DNA sequences around the protein coding regions that control when and how much mRNA is transcribed
eg enhancers, promoters, silencers
can active or repress transcription synergistically or antagonistically
role of activators
recruit PIC proteins
role of mediator protein complex
links activator transcription factors with PIC
co factors
bind to TFs for extra regulation
recruitment of general TFs, modifiers, PIC complex etc
chromatin modifiers
facilitate access to DNA by adding/removing modifications from histones
can modify DNA itself
nucleosome
147 bps
protein core of 8 histones: 2 tetramers of H2A H2B H3 H4 subunits
forms octamer
H1 associates with linker DNA between histones
chromatin remodelling factors
slide along DNA strand to slide nucleosomes relative to each other
exchange histone octamers or subunits (eg is DNA damage is detected, can swap out some histones and put a tag that recruits DNA repair complexes)
remove core histones
alter structure by wrapping more tightly
histone tail modification
by chromatin modifiers
methyl groups and acetyl groups mainly added to lysines
also phosphorylation
effects of acetylation
causes steric interactions
reduce affinity of nucleosome tails to each other
loosen chromatin
recruitment of PIC
effect of methylation
increase affinity of nucleosome tails
recruitment of proteins that repress transcription
attract proteins that pack dna into heterochromatin
exception to methylation
lysine 4 of histones
induces gene expression
