SmartBook Assignment Module 11 - Gene expression regulation
What is an operon?
A cluster of genes under the transcriptional control of a single promoter
What is cyclic AMP (cAMP)?
A small effector molecule involved in the positive control of the lac operon
Gene expression can be regulated in two main ways. Repressor proteins are used for _____ control of gene expression, and activator proteins are used for _____ control of gene expression.
Blank 1: negative Blank 2: positive
An mRNA that encodes more than one protein is called _____ mRNA.
Blank 1: polycistronic, poly-cistronic, or poly cistronic
Regulatory transcription factors that bind to DNA and decrease the rate of transcription are termed _____.
Blank 1: repressors or repressor
What is the CAP site for the lac operon?
The sequence of nucleotides that is recognized by an activator protein
What is the function of the genes encoded by the trp operon?
The synthesis of the amino acid tryptophan
What is the role of repressor proteins in the regulation of transcription?
They bind to DNA and decrease the rate of transcription.
Glucose inhibits lactose metabolism by preventing the production of Blank______.
cAMP
Polycistronic mRNA Blank______.
encodes more than one protein
The genes in the trp operon encode enzymes that make the amino acid _____.
tryptophan
The transcription of the trp operon is turned off when there are high levels of _____ in the cell.
tryptophan, trp, or corepressor
High levels of tryptophan Blank______ the transcription of the trp operon.
will result in a decrease in
How does the presence of lactose in the cell influence the transcription of the lac operon?
-When lactose is present, the lac repressor protein does not bind to the operator site and transcription can occur. -When lactose is present, transcription of the lac operon is high.
What is a corepressor molecule?
A small effector molecule that binds to a repressor protein
What is an inducer?
A small effector molecule that increases the rate of transcription
What is a repressible operon?
An operon that can be inhibited by the presence of a small effector molecule
What is the advantage of operon organization in bacteria?
Bacteria can coordinate the expression of multiple genes in the same biological pathway.
The lac repressor protein prevents the transcription of the lac operon genes by the enzyme _____ _____.
Blank 1: RNA Blank 2: polymerase or pol
A conformational change in the lac repressor protein occurs upon binding of the sugar _____ to it. This change in shape prevents the repressor from binding to the _____ site.
Blank 1: allolactose Blank 2: operator or lacO
When the presence of a preferred energy source inhibits the use of other energy sources, the process is known as _____ _____.
Blank 1: catabolite Blank 2: repression
The small effector molecule that is involved in the positive control of the lac operon is _____ _____.
Blank 1: cyclic or c Blank 2: AMP
The genes found in the lac operon of E.coli are used for the metabolism of _____.
Blank 1: lactose
The lac operon is also under positive control by an activator protein called what?
CAP
An activator protein recognizes the Blank______ of the lac operon.
CAP site
The effector molecule cAMP enhances the transcription of the genes of the lac operon via binding to a protein called _____.
CAP, catabolite activator, or catabolite activator protein
When glucose is present in a bacterial cell, it can act to repress the expression of the lac operon because it is preferentially used compared to other sugars. What form of transcriptional regulation is this?
Catabolite repression
The functional product of genes arises from what process?
Gene expression
How does glucose repress the expression of the lac operon?
Glucose inhibits the production of cAMP, thereby preventing the activation of the lac operon.
The lac operon is an example of what type of operon?
Inducible operon
How does allolactose affect the lac repressor protein?
It binds to the repressor protein and prevents it from binding to the operator site of the lac operon.
What proteins are produced by the three structural genes in the lac operon?
Lactose permease Galactoside transacetylase β-galactosidase
What is the effect of low levels of tryptophan on the transcription of the trp operon?
Low levels of tryptophan will result in high levels of transcription.
What are the basic components of the lac operon?
Promoter lacA lacY lacZ
What does the lac operon region contain?
Promoter, operator, and three structural genes
What are regulatory transcription factors?
Proteins that bind to DNA and affect the transcription of one or more genes
What is the role of the corepressor in the expression of the trp operon?
The corepressor binds to the repressor protein and causes a conformational change, which allows the repressor to bind to the operator site.
What is the function of the genes that are expressed in the lac operon of E. coli?
The metabolism of lactose
The binding of the corepressor to the trp repressor results in what?
The repressor binds to the operator and prevents transcription.
What is the role of the repressor protein in the transcription of the trp operon?
The repressor protein binds to the operator site and prevents the transcription of the trp operon.
How do CAP and cAMP increase the transcription of the lac operon?
When CAP and cAMP bind to the CAP site, this enhances binding of RNA polymerase to the promoter site.
Why is the lac operon considered inducible?
When allolactose is produced, this causes the transcription of the lac operon.
Under what conditions does the lac repressor bind to the operator of the lac operon and prevent transcription?
When the concentration of lactose is low in the cell
The molecule that serves as the inducer of the lac operon is _____.
allolactose
What is the inducer molecule for the lac operon?
allolactose
How does cAMP play a role in the transcription of the lac operon?
cAMP binds to CAP and together they bind to the DNA, which enhances transcription of the lac operon.
When Blank______ binds to CAP, the resulting complex binds to the CAP site near the lac Blank______. This causes a bend in the DNA that enhances the ability of RNA polymerase to bind, and so the transcription rate is increased.
cAMP; promoter
A Blank______-effect is mediated by a DNA element that binds regulator proteins, whereas a Blank______-effect is mediated by genes that encode diffusible regulatory proteins.
cis; trans
Operons enable bacteria to Blank______.
coordinate the regulation of genes with related functions
A small effector molecule that binds to a repressor protein and decreases the rate of transcription is called a(n) Blank______.
corepressor
The process in which the information in a gene is made into a functional gene product, such as an RNA molecule or a protein, is termed gene _____.
expression
Transcription of the trp operon is Blank______ when levels of tryptophan are low in the cell.
increased
A small effector molecule that increases the rate of transcription is called a(n) _____.
inducer
An operon that can be turned on in the presence of a small effector molecule is said to be a(n) _____ operon.
inducible
The binding of an effector molecule increases the rate of transcription of the lac operon. Thus, it is said to be a(n) _____ operon.
inducible
The following diagram shows which type of operon?
lac operon in the absence of lactose
This diagram is a representation of which type of operon?
lac operon in the presence of lactose
Which of the following genes encodes the lac repressor protein?
lacI
The binding of a repressor protein turns off transcription of a gene. This phenomenon is termed _____ control.
negative
When transcription is regulated by repressor proteins, this is called Blank______ control.
negative
The lacO of the lac operon is the site where the repressor protein binds. It is referred to as the _____.
operator
A cluster of genes which forms a single transcription unit that is under the control of a single promoter is termed a(n) _____.
operon
The catabolite activator protein (CAP) is involved in Blank______ control of the lac operon.
positive
The protein encoded by the lacI gene functions to:
prevent transcription of the lac operon
Regulatory transcription factors influence the expression of genes by affecting the rate of transcription. They do so by binding directly to DNA at or near the _____ site.
promoter
An operon in which a small effector molecule prevents transcription is called a(n) Blank______ operon.
repressible
The lacI gene encodes the lac _____.
repressor
The trp operon is regulated by a(n) _____ protein that is encoded by the trpR gene.
repressor
The trp operon is under negative control by a(n) Blank______ protein.
repressor
In the lac operon, the operator is Blank______.
the DNA sequence at which the lac repressor binds
The transcription of the lac operon genes is inhibited when the lac repressor protein binds to Blank______.
the lac operator
The function of the protein encoded by lacI is Blank______.
to repress transcription of the lac operon
Which of the following is a repressible operon?
trp operon
