Topic 7-2 Flashcards
eukaryotic DNA is condensed into chromatin structure and is often:
inaccesible
regulate access to DNA
nucleosome modifications
where do chromatin remodeling complexes bind?
DNA sites and reposition nucleosomes
acetylation of histone proteins _______ nucleosomes and makes DNA _______
destabilize, accesible
what is the function of chromatin remodelling complexes?
to reposition the nucleosomes, allowing transcription factors and RNA polymerase to bind to promoters and initiate transcription
what is the function of acetylation of histone proteins?
alters chromatin structure and permits some transcription factors to bind to DNA
what is an example of histone modifications allowing for gene expression?
acetylation of histones controlling flowering in arabidopsis thaliana (FLC and FLD genes)
a gene that encodes a deacetylase enzyme
flowering locus D (FLD)
what does FLD do?
encodes an enzyme that removes acetyl groups adn restores the chromatin structure, allowing flowering
what does FLC do?
encodes a regulatory protein that represses flowering
how many types of RNA polymerases do eukaryotes have?
three
the promoters of genes trascribed by RNA polymerase II consist of two primary parts:
a core promoter and a regulatory promoter
just upstream of the gene and similar to a bacterial promoter
core promoter
upstream of the core promoter and has a more varied consensus sequence:
regulatory promoter
eukaryotic transcription requires ________ that bind directly to DNA and recruit _______
accessory proteins, RNA polymerases
any DNA binding protein that affects the levels of transcription
transcription factors (TF)
about how many trascription factors are in humans
> 1000
what do TFs do?
bind regulatory promoter sequences and affect transcription by directly or indirectly contacting the basal transcription apparatus
general transcription factors and RNA polymerase II make up the:
basal transcription apparatus
the basal transcription apparatus is sufficient to initiate:
minimal levels of transcription
transcription is frequently controlled by:
DNA binding proteins
many types of DNA binding proteins have evolved with functional parts referred to as:
domains
many types have evolved that share characteristic domains called:
motifs
what are the five main steps to initiate basal transcription in eukaryotes?
1) TFIID binds to the TATA box in the core promoter
2) TFs and RNA pol. II bind to the core promoter
3) transcriptional activator proteins bind to sequences in enchancers
4) DNA loops out, allowing the proteins bound to the enhancer to interact with the basal transcription apparatus
5) transcriptional activator proteins bind to sequences in the regulatory promoter and interact with the basal transcription apparatus through the mediator
the TATA-binding protein (TBP) binds to the:
minor groove of DNA, straddling the double helix
more distant from the gene, but the DNA can loop over allowing interaction with DNA binding proteins and polymerase
enhancers
once RNA pol. II and general TFs are assembled on the core promoter…
- 11-15 bp of DNA unwinds around the transcription start site
- open complex: template strand positioned in RNA pol’s active site
- RNA synthesis begins
after the first ~30 nucleotides are polymerized, RNA pol. II will:
move off the promoter and proceed downstream to elongate the RNA molecule
how many nucleotides of RNA with remain paired with the DNA template strand as transcription progresses downstream?
~8
molecular structure of RNA pol. II and how it functions during elongation have been revealed through the work of:
Roger Kornberg and colleagues
what three things happen after RNA pol. II moves downstream
- the DNA double helix enters RNA pol. II through a cleft in the enzyme and unwinds
- the DNA-RNA duplex is bent at a right angle, which positions the 3’ end of the RNA at the active site of the enzyme
- new nucleotides are added to the 3’ end of the RNA molecule
during eukaryotic termination, RNA pol. I and III have similar mechanisms to:
bacteria
during eukaryotic termination, RNA pol. II continues to synthesize DNA well past the end of the coding sequence, creating:
pre-mRNA
pre-mRNA is cleaved at the consensus site, creating:
- mRNA –> protein
- stil transcribing peice with 5’ hanging
binds 5’ hanging end and “eats” its way to the polymerase/transcription –> causes termination
exonuclease protein Rat1
