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Genetics, Third Exam: Lac Operon
Exam is on Chapters 16 & 17. This is just one segment
Terms in this set (50)
Regulation of gene expression permits what?
Regulation of gene expression improves efficiency.
What does it mean for a gene to be inducible?
Inducible genes are expressed only for specific conditions; they must be turned on. They often encode enzymes that catabolize a molecule.
What does it mean for a gene to be repressible?
A repressible gene is a gene whose transcription and expression are stopped when expression is no longer needed.
What is the molecule responsible for repressing gene expression of repressible genes?
Repressor. The repressor is often the end product of the biosynthetic pathway controled by the enzymes expressed by the gene.
Give an example of an inducible gene
What molecule is responsible for turning on a gene that is currently off?
This molecule is called the inducer; it induces transcription of the inducible gene, activating gene expression.
Describe positive regulation.
Positive regulation occurs when a regulatory molecule activates transcription. It binds the DNA and helps RNA polymerase bind to the promoter.
Describe negative regulation.
Negative regulation occurs when the regulatory molecule bind to the DNA and prevents the RNA polymerase from binding, thereby blocking transcription.
What role do metabolites play in gene expression?
The presence or absence of metabolites can turn a gene on or off.
What is a constitutive gene?
A gene that is transcribed at a relatively constant level regardless of the cell environmental conditions.
How may gene expression be regulated?
Gene expression may be under positive or negative control.
What is an activator?
An activator is a regulator molecule responsible for positive regulation of a gene.
What is a repressor?
A repressor is a regulator molecule responsible for negative regulation of a gene.
What defines the behavior of regulation molecules?
How do prokaryotes regulate multiple genes in a Metabolic pathway?
They group the genes on one operon. These are a defined group of genes on the control of one promoter. This produces polycistronic mRNA.
Where does the regulatory protein bind?
Promoter and operator
What scientists first figured out the Lac Operon? What else are they known for?
Jacob and Monod. They also first postulated the existence of mRNA.
The lac operon is under what kind of regulatory conrol?
Negative (but is also inducible)
The lac operon is involved in the metabolism of ___________.
Lactose is a ___________.
What is the chemical break down of lactose?
Lactose----> Glucose + Galactose
Give a general description of the lac operon.
The Lac Operon has structural genes, with an upstream regulatory region consisting of an operator (lacO) and a promoter (lacP)
What are the structural genes of the lac operon?
lacZ - beta-galactosidase (necessary to turn lactose into monosaccharides)
lacY - lactose permease (necessary to get lactose into the cell)
lacA - thiogalactoside transacetylase (not necessary for lactose metabolism)
What is the lacI gene?
The LacI gene encodes the repressor protein, which is a negative regulator of the transcription of the three structural lac genes.
Give an example of a constitutive gene.
The lacI gene is constitutive. (It is the structural segment of the lac operon that is inducible)
What is β-galactosidase?
Galactosides are a particular group of organic molecules. β-galactosidase is encoded by the lacZ gene. It is an enzyme that cleaves lactose in to monosacharides and converts lactose to allolacose.
What is encoded by the lacY gene?
What is encoded by the lacA gene?
What is so great about Monosaccharides?
They are useable; they are faster to metabolise than disaccharides.
What converts lactose to allolactose?
What is the permease function?
Permease transports lactose into the bacterium.
What is the function of transacetylase?
Likely protects the cell from toxic products created by action β-gal
Glucose and galactose are both______________
What is inducer for the lac operon?
How many regulatory elements does the lac operon have?
What are regulatory elements?
Segments of DNA involved in regulation of structural gene transcription.
What is the repressor gene of the lac operon?
What are the products of the LacI?
What does the LacI product do?
Binds the operator
What constitutes the regulatory region of the lac operon?
Promoter & Operator.
What is the function of RNA polymerase?
RNA pol binds the promoter to begin transcription.
What does the repressor protein bind?
What is the operator region?
The region between the promoter and structural genes to which the repressor protein binds. It enables control of structural gene expression.
The repressor protein has ______ binding sites, the _____________ and ___________.
The repressor protein has 2 binding sites, the operator region and allolactose region.
In the absence of lactose, the repressor protein ________
binds the operator.
If the repressor protein binds the operator, ________________________
RNA polymerase cannot initiate transcription.
What happens in the presence of lactose?
Allolactose binds the repressor protein and transcription is initiated.
What happens when Allolactose binds the repressor protein?
This binding causes a conformational change. The change alters the operator binding site and the repressor protein falls off the operator. RNA pol can now transcribe structural genes.
The lac operon repressor protein can be described as what kind of protein?
An allosteric protein.
When lactose is present, ezymes are required to metabolize it in order to produce allolactose. How does the cell get around this problem when the lac operon is repressed in the absence of lactose?
β-gal is made even in the absence of lactose because this enzyme is needed in case lactose becomes available. Transcription for the lac operon is not 100% inactive in the absence of lactose; enough transcription occurs to counter this conundrum.
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