Card Set Information
gene expression in prokaryotes
Which of the following are used to regulate gene expression and function? (3)
What best defines the term operon?
-an operon is a region of DNA that codes for series of functionality related genes under the control of the same promoter
Under which conditions are the lac structural genes expressed most efficiently? (2)
- no glucose and high lactose
In what 3 levels can gene expression be controlled at?
What is the lac operon?
a model system for understanding fundamental mechanisms regulating gene expression
What two types of transcriptional control can a regulatory protein induce?
negative and positive
(transcriptional control) Negative control
(transcriptional control) Positive control
increases the transcription rate
Regulatory proteins AND distinct amino acid sequence AND type binds to different DNA sequences
Each type of regulatory protein has a distinct amino acid sequence therefore each binds to different DNA sequences
(regulation of gene expressions ) Transcriptional control (2)
- we can regulate to determine whether or not we will let RNA polymerase to produce a transcript
-it is slow but efficient with the energy expenditure
(regulation of gene expressions ) Transcriptional control (2)
-whether or not we will end up producing the protein from the ribosome
-allows quick change to which proteins are produced
*expends little energy
(regulation of gene expressions ) Post translational control (3)
-we can produce the protein then decide if it will have a potent function by modifying it
*putting a phosphate
-very rapid response
WHat two conditions does E.coli make machinery to process lactose? (2)
-no glucose around
-lots of lactose around
What is the galactoside permease?
protein that gives a channel to cross over the hydrophobic membrane
What is the Beta galactoside?
enzyme that breaks up lactose up into single units
*glucose and galactose
What are the two proteins that process the lactose?
What is lactose broken into? (2)
glucose and galactose
Mutant Phenotype: Cells cannot cleave indicator molecule even if lactose is present as an inducer
-gene for beta glucosidase is defective
Mutant Phenotype: Cells cannot accumulate lactose inside the cell
-No membrane protein required for import of lactose
-gene for galactoside permease is defective
Mutant Phenotype: Indicator is cleaved even if lactose is absent (no inducer)
-constitutive expression of lacZ and lacY
-gene for regulatory protein that shuts down lacZ and lacY is defective
-it does not need to be induced by lactose
What does lacZ + stand for?
does produce beta galactosidase
What does LacZ- stand for?
does not produce beta galactosidase
What does lacY+ stand for?
produces galactoside permease
What does LacY- stand for?
does not produce galactoside permease
produces the 2 proteins without lactose inducing the repressor
Does E.Coli continuously produce the 2 proteins?
no, because making these proteins expends alot of energy
What is a polycistronic system?
expression of many genes are turned up or down by a single regulatory factor
Which is the regulator in the lac operon?
(Regulation of the lac operon diagram) diagram A (4)
-repressor binds to DNA
-no transcription occurs
(Regulation of the lac operon diagram) diagram B (4)
-lactose binds to repressor causing to release from DNA
*acts as inducer
(Regulation of the lac operon diagram) diagram C (3)
-no repressor present
-lactose present or absent
What is the inducer of this system>
lactose induces this change
What is a domain?
a distinctive 3 dimensional structure and function that proteins have
What is a motif?
domain that is observed in many different proteins
What is a common structural design in the lac repressor?
What does helix turn helix do?
the motif fits easily into the major groove of the DNA double helix
What binds to operator region?
What binds to the promoter regions ?
What is negative control? (2)
-regulatory protein shuts down transcription
-repressor protein is normally present preventing transcription which saves energy
In the system when we have lactose inducing the prodcution of genes, is that negative control?
What is positive control?
regulatory protein triggers transcription
Regulation of the gene products of the lac Z and LacY by LacI is an example of?
(regulation of the lac operon by glucose) Catabolite repression
when glucose levels are high, trasncription is turned off even if lactose levels are high
*example of feedback inhibition
(regulation of the lac operon by glucose) Catabolism formula
-large reactant molecule >(enzyme)> small product molecule + small product molecule (catabolites
ex) Lactose >Beta galactosidase> galactose + glucose
(regulation of the lac operon by glucose) Catabolism
break down of a large product into small ones
(regulation of the lac operon by glucose)(catabolite repression) How does glucose inhibit hte catabolite repression?
glucose does not directly bind to DNA or RNA to inhibit process, it alters the concentration of other molecules
(regulation of the lac operon by glucose)(catabolite repression) WHat triggers transcription?
the CAP binds to the CAP binding site near the lac promoter
(regulation of the lac operon by glucose)(catabolite repression) What are the effects of the CAP binding?
lac promoter increases expression
(regulation of the lac operon by glucose)(catabolite repression) How is CAP regulated?
by cyclic AMP (cAMP) binding to it
(regulation of the lac operon by glucose)(catabolite repression) what needs to happen in order for the CAP to bind well with the DNA?
CAP needs to be binded with cAMP
(regulation of the lac operon by glucose)(catabolite repression) What happens if cAMP levels are low?
CAP is not active and transcription is not increased
(regulation of the lac operon by glucose)(catabolite repression) What happens when cAMP levels are high?
CAP protein binds to DNA and speeds up trasncription
(regulation of the lac operon by glucose)(catabolite repression) What does glucose lower the concentration of?
cAMP by altering the activity of the adenylate cyclase (makes cAMP)
(regulation of the lac operon by glucose)(catabolite repression)What happens if there is a large number of glucose present?
leads to a drop on cAMP
If cAMP are high, will we get an increase in beta glucosidase and mRNA?
Do we get an increase in beta glucosidase when glucose levels are high?
no, we dont need to produce enzymes and proteins needed for lactose