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42 Cards in this Set

  • Front
  • Back
Proaryotes regulate gene expression in response to what?
Environmental Conditions
Enzymes in gene regulation may be (3 things)
Inducible (adaptive), constitutive, and repressible
Regulation may be under (2 things)
Positive Control and Negative control
Regulatory elements that are almost always located upstream of the gene cluster they control
The molecules that bind cis-acting sites
Trans-acting elements
Lactose Metabolism in E. Coli is regulated by an
Inducible System
-were the enzymes responsible for lactose metabolism are inducible and lactose is the inducer
Has 3 strucural genes (lacZ, lacY, and lacA) with an upstream regulatory region consisting of an operator and a promoter.
Lac operon
The lacZ gene encodes what enzyme that converts the disaccharide lactose to the monosaccharides glucose and galactose?
The lacY gene specifies the primary structure of what enzyme that facilitates the entry of lactose into the bacterial cell?
The lacA gene codes for what enzyme that may be involved in the removal of toxic by-products of lactose digestion from the cell?
The structural genes of the lac operon are transcribed as a
Polcistronic mRNA (see slide 6 for picture)
Scientists who proposed the the operon model in which a group of genes is regulated and expressed together as a unit
Jacob and Monod
Why is the lac operon subject to negative control?
Because transcription occurs only when the repressor fails to bind to the operator region. (See slides 8-10)
The lacI gene regulates transcription of the structural genes by producing what?
A repressor molecule
The repressor created by the lacI is _______, meaning that it interacts reversibly with another molecule, causing both a conformation change in 3-d shape and a change in chemical activity
What did the analysis of lac expression in the absence or presence of lactose in partial diploid merozygotes prove?
The operon model for the lac operon (Slides 13 & 14)
What exerts positive control over the lac operon and is involved in repressing expression of the lac operon when glucose is present?
Catabolite-Activating Protein (CAP)
Inhibition from the catabolite-activating protein
Catabolite repression
In the absence of glucose and the presence of lactose...
CAP exerts positive control by binding the CAP-binding site and faciliatating RNA polymerase binding at the promoter (See slide 17)
For maximal expression, the repressor must not be...
And CAP must be...
bound at the operator
bound at the CAP-binding site
What is required for CAP binding
cyclic adenosine monophosphate (cAMP)
Glucose represses expression of ____________, the enzyme that catalyzes the production of cAMP, and thus prevents CAP from binding when glucose is present.
Adenylyl cyclase
Confirmed the Operon Model
Crystal Structure Analysis of Repressor
A detailed structure of the lac operon and regulatory regions reveals how many sites for repressor binding? And why must all three operators be bound?
3 sites
For maximum repression
See Slide 20
Binding of the repressor to operators O1 and O3 creates a ________, which prevents access of RNA polymerase to the promoter.
Repression loop
1. The Tryptophan Operon in E. Coli is a ...
2. The enzymes for tryptophan production form an...
3. In the presence of tryptophan, the (answer to #2) is ....
1. Repressible Gene System
2. Operon
3. Repressed
Tryptophan functions as a _________, which is required for the repressor to bind to the operator.
Corepressor (See slides 23-25)
The trp structural genes are preceded by a leader sequence containing a regulatory site called an...
The mechanism by which expression of the rest of the trp operon is repressed after transcription of the leader sequence.
In the absence of tryptophan, transcription is...
Not terminated in the leader region and proceeds through the entire operon.
In the presence of tryptophan, the hairpin structures formed act as a transcriptional ________.
In the absence of tryptophan, a different hairpin forms and acts as an __________, and transcription proceeds.
antiterminator (Slide 30)
Contains two tryptophan codons
Leader region
Forms in the abscence of tryptophan because the ribosome stalls at these codons as there is not adequate charged tRNA(trp)
The antiterminator hairpin structure
In the presence of tryptophan, the ribosome proceeds through this sequence and the __________ can form.
Terminator hairpin
The attenuation mechanism is common to several operons for enzymes responsible for synthesis of other amino acids such as...
(don't know if we'll need to know this)
Threonine, histidine, leucine, and phenylalanine
Instead of ribosome stalling, the mechanism of attenuation for the trp operon involves a protein called_______. It has 11 subunits, each of which can bind one molecule of tryptophan. When fully saturated, it can bind to the 5' leader sequence to form the terminator hairpin and prevent formation of the antiterminator hairpin.
TRAP (trp RNA-binding attenuation protein)
See slide 35.
Uncharged tRNA(trp) induces expression of the...
anti-TRAP(AT) gene
_________ associates with TRAP in the tryptophan-activated state and inhibits binding to the target leader RNA sequence.
The AT protein
The ara Operon is controlled by a regulator protein that exerts...
...both positive and negative control
_________ is subject to both postive and negative regulation by the _AraC_.
Arinose (ara) operon
_______ interacts with 2 regulatory regions: araI and araO2. It also bnds to araI in the presence of arabinose and CAP-cAMP to induce expression. In the absence of arabinose and CAP-cAMP, it binds to both araI and ara O2 to form a loop that causes repression.
AraC (See slide 39-40)