MCB 2050 Molecular Biology of the Cell -
W21 complete midterm exam notes (get well
prepared) University of Guelph
Gene Regulation
Gene Expression, RNA polymerases and Promoters
Control of Gene expression in Bacteria
- Prokaryotic gene expression is regulated by simple mechanisms that control transcription by
RNA polymerase
- A group of proteins called σ factors recognize promoter elements (-10, --35) and load RNA
polymerase at the start site
- Transcription activators and repressors regulate the loading and release of RNA polymerase
o Most bacteria and single-celled organisms regulate gene expression to adjust cell
enzymatic machinery and structural components to change in nutritional and physical
environment
o Bacteria cells normally synthesize only proteins that are required for survival under
current conditions
The lac operon (structural gene) is a classic example of a regulated prokaryotic promoter
- activated by an activator protein (CAP, catabolite activator protein), that binds next to a
promoter and recruits RNA polymerase
- the lac operon is repressed by a repressor protein (lac repressor)
RNA polymerase
- Binds to -10 position
- Needs a σ factor to initiate transcription
- σ factor associates with -30 protein
- -10 and -30 elements act as basal
elements found in all promoters
Bacterial gene expression is regulated by simple
transcriptional activators and repressors that
bind promoters of the gene
- CAP activator: binds to CAP site
- Lac repressor: binds to operator
, lOMoARcPSD|6353920
Lac repressor (Lac I) binds to DNA downstream of
transcription initiation site and prevents
transcription by RNA polymerase
- Presence of lactose drives the binding of
Lac repressor to its binding site
CAP (catabolite activator protein)
- Activated by cAMP (glucose -)
- Binds to DNA upstream of initiation site
and stimulate recruitment of RNA
polymerase
, lOMoARcPSD|6353920
In absence of glucose (↑cAMP, CAP binds the
promoter) and in presence of lactose (LacI
doesn’t bind to promoter)
- The lac operon is expressed
, lOMoARcPSD|6353920
Eukaryotic gene Control
- The primary purpose of gene control in multicellular organisms is the execution of precise
developmental programs
o So that the proper genes are expresses in the proper cells at the proper times during
embryologic development and cellular differentiation
o In eukaryotes we have three RNA polymerases
o In eukaryotes, general transcription factors are involved in elaborate process of
recognition of promoter element and assembly of pre-initiation complex then load RNA
polymerase
- In eukaryotes, transcription takes place on DNA that is wrapped in chromatin
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller smartzone. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £12.28. You're not tied to anything after your purchase.
