prokaryotic regulation regulation of gene expression – part i spring 2013 - althoff reference:...
TRANSCRIPT
• Prokaryotic Regulation
Regulation of Gene Expression – Part ISpring 2013 - Althoff Reference: Mader & Windelspecht Ch. 13)
Lec18
• 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:
1
3 4
5
2
• _______________ – 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 Elements1
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 Elements4
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 Controlof gene expression
Negative Control of gene expression