Gene Expression Control I Flashcards
What is RNA sequencing?
Every single RNA ina
cell is isolated from cells and sequenced
What is beta-actin?
A major component of the cell cytoskeleton and is expressed in all cells
What is tyrosine aminotransferase?
Enzyme that is only expressed in liver hepatocytes.
What does constitutively expressed?
The gene is always on
What can happen to genes before and after differentiation?
Some genes are turned on
Some genes are turned off
Some genes are constitutively expressed
Does RNA differences indicate protein differences?
No, RNA expressed in a cell does not always reflect large difference in protein expression in the cell. Proteins can be modified after they are expressed.
What percentage of genes are expressed in a typical human cell?
30 - 60%
What factors influence gene expression?
Signals:
Cell-cell contact
Hormones
Morphogens
Transcription factors
What are morphogens?
Molecules that specify cellular identity: Concentration of these is important.
Many morphogens are transcription factors
What are transcription factors?
Proteins which bind to regulatory elements of a gene. They control transcription and are often activated in response to external stimuli.
2 main catergories; general or tissue/cell specific.
Where in the promoter region do transcription factors bind?
Assembly of transcription factors and transcription machinery occurs in the TATA box.
What are the levels of regulation of gene expression?
DNA -> RNA (transcription control)
RNA processing to mRNA control
mRNA transport and localization control
Translation control
mRNA degradation control
Protein activity control
What is the primary means of regulating gene expression?
Transcriptional control.
cis-acting control elements regulate transcription
What are promoters?
Sequences that determine the transcription start site and direct binding of RNA pol II
What do enhancers and repressors do?
They help regulate a particular gene and are often tissue specific and function only in specific diffrentiated cell types
Where are promoters located?
Near start site (5’ end)
Where are enhancers located?
Anywhere near the gene and may also be many kb away
What do cis-acting control elements do?
They regulate transcription
What is combinatorial control?
Eukaryotic genes are controlled by combinations of transcription factors binding to DNA binding sites in the promoter this form of control is called combinatorial control
What is combinatorial control of gene expression dependent on?
DNA sequences present
TFs present
Interactions between regulatory proteins.
How do transcriptional elements and bound TFs interact with the RNA pol?
DNA/TF complex loops back to interact with the TATA factors. They stabilize the binding between RNA pol and the TATA box.
What do TFs do to transcription initiation?
They serve to increase or decrease the rate of transcription initiation.
What are some examples of transcription factors?
Leucine zipper proteins (2 alpha helices that bind major group of DNA that it is specific to)
Helix-Loop-Helix proteins (Bind directly to a specific sequence of DNA like leucine zipper (using 2 alpha helices)
What domains do regulatory proteins commonly have?
Domain that recognizes correct DNA promoter or enhancer element
Domain that interacts with one or more proteins of the initiation complex
Domain that interacts with TFs bound to their cis-element
Domain that influences chromatin remodelling
Domain that acts as a sensor of conditions within or outside the cell
How do transcription factors work together (cooperative binding)?
Sometimes they only have an important effect on transcription when they are combined together. (eg NFAT and AP1 cooperative binding)
How do glucocorticoid receptors work?
When hormone binds to its receptor, the TFs bounds to the receptor can be translocated to the nucleus.
How does chromatin environment affect transcription?
Tightly packaged regions are not expressed and are called heterochromatin
Non-tightly packaged regions are expressed and are called euchromatin.
What does nuclease (DNase I) do?
Digests DNA dependent on access to the DNA and chromatin structure. DNase I sensitivity depends on gene activity (more active = more digestion)
