Control of Gene Expression in Prokaryotes

Question 1

What is an operon?

Answer 1

An operon is a cluster of genes, transcribed as a single mRNA, that regulate gene expression levels.

Question 2

What is the Jacob-Monod Model?

Answer 2

The Jacob-Monod Model is a specific structure of an operon. Upstream you have a regulator region/sequence, followed by a promotor region, an operator region, and then structural sequence.

• The structural gene codes for the protein of interest that is having its expression regulated
• The operator is a nontranscribable region that binds a repressor if needed.
• The promoter region is the site/location where RNA polymerase (RNAP) binds to DNA.
• The regulator gene codes for a repressor protein that prevents the structural gene from being transcribed.
  
  • Repressor protein blocks RNAP from moving downstream to transcribe.

Question 3

What are the two different types of operon systems?

Answer 3

The two different types of operon systems are inducible and repressible systems.

• In an Inducible Operon System, the repressor is always bound to the operator region until an inducer is present to bind to the repressor. When the inducer binds to the repressor, it prevents the repressor from binding to the operator region and the protein is made.
  
  • Postive Control Mechanism: causes production
  • Ex: Lac Operon
• In a Repressible Operon System, there is constant production of the protein. The repressor must have a corepressor bind to it in order for the repressor to bind to the operator region. Once the repressor-corepressor complex is bound, protein production ceases.
  
  • Negative Control Mechanism: stops production
  • Ex: Trp Operon

Question 4

What is the difference between a region and a gene in DNA?

Answer 4

A gene is transcribed whereas a region is not and is involved with regulation.