5. Control of Gene Expression and Transcription
Chromatin
Nucleosomes
Upstream
Downstream
Chromatin Remodeling
30-nm Fiber
Silencer
Activators
Exon/ Intron
Promoter Proximal Elements
Alternative Splicing
Mediator Complex
DNA Regulatory Regions
o Enhancer
o Silencer
o Promoter Proximal Sequence
Promoter
Acetylation
Repressors
Enhancer
Proteins
o Activator
o Repressor
o RNA Polymerase
1. Describe the process that takes place to form the chromatin.
Chromatin formation can be put in this sequence:
1)
DNA Double Helix wraps around the 8 histone proteins.
2)
The H1 protein attaches to linker DNA and the nucleosome.
3)
A 30-nm fiber is formed when nucleosomes interact.
4)
The chromosome forms.
2. Determine whether every cell in our body has the same genome or not. Then
determine how this relates to variance in protein production.
Every single cell in our body contains the same genome. However, since
not every gene is expressed (transcription and translation), different kinds of
proteins are synthesized in cells of different tissues. Consider as an example
the abundance of the protein myosin in muscle cells and the abundance of
Na+/K+ pumps – they are proteins – in nerve cells.
3. Draw on a linear DNA double helix: Refer to the PDF on the SI website.
a. Where introns, exons, enhancers, silencers, and promoter proximal sequences
would be;
b. Where the following proteins would bind: activators, repressors, and RNA
polymerase;
c. Put Extra Thought: What is the TATA box? Where would it be located on the
DNA and what is the protein that binds it?
TATA box is a specific promoter sequence located almost in every cell
of our body. The protein that binds it is TATA bob binding protein (TBP).
4. Describe how the mediator complex brings together regulatory transcription factors
and basal transcription factors.
A transcription factor is an assembly of proteins. Basal transcription factors
interact with the promoter and are not cell specific – they are also required for
transcription. Regulatory transcription factors interact with enhancers,
silencers, and promoter-proximal sequences and are responsible for
transcription of only some genes – depending on the type of cell.
The mediator complex binds basal transcription factors and regulatory
transcription factors at the same time, bringing them together in order for
regulatory transcription factors to control gene expression. [Think of a
sandwich. The bread would be transcription factors and the jelly is the
mediator complex that holds the two bread slices together].