Chapter 15; The Jacob-Monod model for gene regulation
Regulation of gene activity via the operon
Enzymes may be divided into two categories
Constitutive enzymes are always present
Regulative enzymes may or may not be present
What controls the regulative enzymes; a problem of turning genes
on and off
Answer via mutation analysis
Mutations may be in structural genes (for enzymes) or
regulation sequences of DNA
Wild type E.
coli will produce the enzyme beta-galactosidase when
lactose is present.
Some mutant E.
coli will produce beta-galactosidase if lactose is present
or absent; they are constitutive mutations
Other mutations are in the beta-galactosidase gene
The model:
Location of the lac operon.... OperonMap.GIF
Model of a portion of the E. coli chromosome: operon2.GIF
Concept of the allosteric protein operon3.GIF
Lactose not present....operon4.GIF
Analysis: Mutations of the lac operon
Mutation in repressor gene...repressorS.GIF
Genotypes and the operon model (some partial diploids for cis
trans analysis)
important: repressor protein may act on all
chromosomes - trans acting
important: operator DNA cis acting
A tutorial which may help with the complex genotypes OperonHome.html
In gene regulation we have cis vrs trans effects.
for cis, the effect must be between adjacent segments
of DNA
for trans, there is some movable
object which may influence another chromosome
cover of Science 1 March 1996