Biology 1002B Lecture Notes - Lecture 8: Tata-Binding Protein, Histone Acetyltransferase, Tata Box
13 Jun 2018
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Lecture 16 Outcomes:
Basic structure of eukaryotic vs prokaryotic cell with respect to gene expression
- Prokaryotes: are primarily controlled through transcription (because when the protein is no
longer needed, transcription stops)
- due to the lack of a defined nucleus; the DNA is free floating within the cytoplasm and
therefore both transcription and translation occur in the cytoplasm this also allows for
the DNA to be translated and transcribed at the same time
- operons
- Eukaryotic: regulation occurs after the DNA is uncoiled and loosened from nucleosomes and
is able to bind transcription factors
- DNA is transcribed (in the nucleus), then the mRNA is processed and exported to the
cytoplasm (post-transcriptional level), then the RNA is translated into protein on ribosomes
(translational level)
- there is also further modifications that can be made after translation (post-translational
level)
- have more options to regulate expression
Structure of eukaryotic promoters
- RNA polymerase II promoters have a TATA box that attracts TATA binding protein (which
assists in the formation of the RNA polymerase transcriptional complex)
Role of chromatin packaging and histone modification in transcription initiation
- the nucleosomes in normal chromatin prevent general transcription factors and RNA
polymerase II from binding so transcription does not occur
- regulatory transcription factors can bind to the DNA and lead to a change in chromatin to
make it active so transcription can occur
- A key regulatory event for regulating transcription initiation, then, is controlling the transition
between the inactive and active states of chromatin in the region of a promoter
- In inactive chromatin, the histone tails are not acetylated so the DNA is wrapped tightly
around the histone octamer
- when a regulatory transcription factor binds to a regulatory sequence associated with the
gene, a protein complex histone acetyltransferase acetylates (adds acetyl groups) to the
histone tails
- the acetylation changes the charge of the histone tails causing them to let go of the DNA
- DNA methylation: when the DNA is methylation is becomes highly coiled, which prevents
transcription factor from binding, therefore transcription cannot occur
Transcription Initiation
- Transcription factors recognize and bind to the TATA box (upstream of the start point for
transcription inside the promoter) then the RNA polymerase II is called
- further upstream from the promoter is the promoter proximal region (it contains regulatory
sequences called promoter proximal elements)
- Regulatory proteins that bind to promoter proximal elements may stimulate or inhibit the rate
of transcription initiation
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- Regulatory proteins binding to regulatory sequences within an enhancer also stimulate or
inhibit the rate of transcription initiation
- DNA binding domains are specialized parts of a protein that allow it to bind with DNA
- to initiate transcription, general transcription factors bind to the promoter region (near the
TATA box) to help RNA polymerase II bind
- the transcription initiation complex (RNA polymerase II & transcription factors) only produce a
few copies of transcript on their own (not efficient)
- Activators that bind to the promoter proximal elements interact directly with the general
transcription factors at the promoter to stimulate transcription initiation so many more
transcripts are synthesized in a given time
- repressors can also bind at the enhancer (blocking the activator from binding), they inhibit
transcription initiation
- Co-activators are multi protein complexes that form a bridge between the activators at the
enhancer and the proteins are the promoter proximal region to greatly increase the rate of
transcription
Protein motifs common in DNA binding proteins
- Protein motifs functions as activators
- Helix-turn-helix: motif is part of a protein bound to DNA, one of the alpha-helices binds to the
base pairs in the major grooves of the DNA, a looped section of the protein (the turn)
connects the second alpha-helix to hold the 1st one in place
- Zinc finger: are parts of proteins named for their resemblance to fingers projecting from the
protein, and the presence of a bound zinc atom, they bind to specific base pairs in the
grooves of DNA
- Leucine zipper: proteins are dimers, with each monomer consisting of alpha-helix segments
Hydrophobic interactions between leucine residues within the leucine zipper motif holds
the 2 monomers together. Other alpha-helices bind to DNA base pairs in the major groove
Mechanism of splicing and the advantages to alternative splicing - RNA processing
- splicing occurs in the nucleus to pre-mRNA as a part of RNA processing by removing introns
and joining exons together
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Basic structure of eukaryotic vs prokaryotic cell with respect to gene expression. Prokaryotes: are primarily controlled through transcription (because when the protein is no longer needed, transcription stops) Eukaryotic: regulation occurs after the dna is uncoiled and loosened from nucleosomes and is able to bind transcription factors. Dna is transcribed (in the nucleus), then the mrna is processed and exported to the cytoplasm (post-transcriptional level), then the rna is translated into protein on ribosomes (translational level) There is also further modifications that can be made after translation (post-translational level) Rna polymerase ii promoters have a tata box that attracts tata binding protein (which assists in the formation of the rna polymerase transcriptional complex) Role of chromatin packaging and histone modification in transcription initiation. The nucleosomes in normal chromatin prevent general transcription factors and rna polymerase ii from binding so transcription does not occur.
