Chapter 15; The Jacob-Monod model for gene regulation

pictures of Jacob and Monod ... JacobMonod1965.GIF

 

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

Two types of mutations.... OperonMutationsFinal.GIF

 Key phenotypes ......... operonPhenotypes.gif

Key genotypes ...... operonKeyGenotypes.gif

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

Lactose present....operon5.GIF

Simple movie: ... operonmovie.gif

Another .... OperonMovie.html

Reality: structure of repressor...OperonModelScience.GIF 

Show cover of Science 1 March 1996

Partial DNA sequence for operon (not on web) .. operonDNA

Analysis: Mutations of the lac operon 

 

Mutation in repressor gene i^- ... repressorminus.GIF

Mutation in repressor gene i^s...repressorS.GIF

Mutation in operator o^c ... OperatorMutation.GIF

Overview... OperonMutationsOverview.GIF.

...................................................

important: repressor protein may act on all chromosomes - trans acting

important: operator DNA cis acting

 

List of steps.....operonWorkbook2.gif 

from workbook: operonWorkBook.gif

 

A tutorial which may help with the complex genotypes OperonHome.html

In gene regulation we have cis sequences vrs trans acting molecules.

for cis, the effect must a sequence of DNA on the same chromosome

for trans, there is some movable object which may influence another chromosome