Prokaryotic Regulation Regulation of Gene Expression – Part I Spring Althoff Reference: Mader & Windelspecht Ch. 13) Lec 18

Bacteria do not always ________ their entire complement of enzymes and proteins …because their environment is ever changing. In 1961, French microbiologists Francois Jacob and Jacques Monod showed that Escherichia coli is capable of regulating the expression of its genes. They observed that ________________ for a __________________ are grouped on a chromosome…and transcribed at the same time Prokaryotic Regulation

The ___________ Model Jacob and Monod proposed a model to explain gene regulation in prokayotes An operon has these components:

_______________ – normally located outside the operon. Codes for the DNA-binding protein that acts as a ______________ _____________ - a _______________ of DNA where RNA polymerase first attaches to begin transcription (remember this happens in the nucleus) of the grouped genes. The Operon Elements 1 3 2

__________– a short portion of DNA where an active repressor binds. When present, RNA polymerase _____________ to the promoter— thus ____ transcription possible _________________– genes that ______ for the enzymes and proteins that are involved in the metabolic pathway of the operon The Operon Elements 4 5

Jacob and Monod…and others…found that some E. coli operons usually existed in the “___” condition vs. the “____” condition This means tryptophan is not presence and the active repressor is “inactive” When “___”, their products—5 different enzymes— are part of _________________ for the synthesis of the amino acid tryptophan. If tryptophan present in the medium, then these enzymes are not needed…and the tryptophan _____ to the repressor making it an __________________ The trp Operon: on vs. off

The trp operon – making or not making tryptophan Tryptophan ABSENT…enzymes needed are produced ▲Tryptophan ABSENT…needed enzymes not produced A A B B

When the trytophan binds to the repressor, it ________________…result: RNA polymerase can’t bind to the polymerase The trp Operon: on vs. off…con’t

The lac Operon Bacteria metabolism is very efficient…when there is ___________ for certain proteins or enzymes, the genes needed to make them are usually inactive. Example: if the milk sugar lactose is not present, there is no need to “___________” genes for enzymes involve in lactose ____________. There are ________ encoded for the enzymes needed to break down lactose: β-galatosidase, permease, and transacetylase.

The lac Operon…con’t The 3 structural genes that code for producing those enzymes are ____________ to one another… …and are under control of a __________ promoter and a ___________ operator. Because the presence of lactose brings about expression of genese, it is called an ___________ of the lac operon The entire “unit” is called an ________________ because they have “inducible” enzymes.

Further Control of the lac Operon E. coli preferentially breaks down glucose…and the bacterium has a way to ensure that the lactose operon is maximally turned on ______ when glucose is absent. Cyclic AMP (cAMP) _____________ when glucose is absent. cAMP, which is a derivative of ATP, has a single phosphate group—which is attached to the ribose at two locations

cAMP binds to a molecule called catabolite activator protein = _____…and that complex attaches to the CAP binding site next to the lac promoter. When CAP binds to DNA, ____________, exposing the promoter to RNA polymerase…. …the result: RNA polymerase is now __________ to bind to the promoter aiding transcription which leads to their expression More on cAMP…

Lactose present, glucose absent…cAMP level _______ Lactose present, glucose absent…cAMP level _____

CAP’s protein regulation of the lac operon is an example of _________ control. Why? When CAP is active it ___________ the activity of the operon. Positive Control Negative Control The use of repressors is an example of a _________ control Why? When the repressor is active ____________ the operon.

Positive Control of gene expression Negative Control of gene expression