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repressors
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∙ 12y ago
A repressor protein turns off transcription by binding to the operator region. By binding to the operator, the repressor prevents the RNA polymerase from binding to the promoter region and initiating transcription. This prevents the expression of the gene or genes downstream of the operator.
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What is a repressible operon?
is one that is usually on; binding of a repressor to the operator shuts off transcription
In E. coli the tryprophan switches off the trp operon by?
Binding to the repressor and increasing the latter's affinity for the operator
Describe how E. coli uses the negative and positive control of the lac operon to economize on RNA and protein synthesis?
if a regulatory protein in its active state turns off the expression of the operon, the operon is said to be negatively regulated by the regulatory protein. if the regulatory protein in its active state truns on the operon, the operon is positively regulated by the regulatory protein. an operon regulated by a repressor is therefore negatively regulated, because the presence of the active repressor prevents transcription of that operon. in contrast, an operon regulated by an activator is positively regulated, because in its active state the activator protein turns on transcription of the operon under its control. the lac operon of E. coli repressor(lac repressor) is synthesized through the activity of the gene lac I, known as regulator gene. the active form of the lac repressor, is a tetramer that contains four copies of the gene I product. in the absence of the inducer, the repressor binds to the lac operator sequence, preventing RNA polymerase from binding to the promoter and transcribing the structural genes. thus the lac operon is negatively regulated associated with the lac operon, there is another site, 16 base pairs upstream of the promoter, which is used for a positive control of the gene expression. this site is called catabolic activator protein site or cyclic AMP(cAMP) protein site or catabolite gene activator(cga) site, because it is utilized for binding of CAP or cga to stimulate gene expression. CAP can bind to this site only when it is bound with cAMP. by binding to it, the CAP-cAMP complex exerts a positive control over the transcription process. it has an effect exactly opposite to that of repressor binding to an operator. yhe effector molecule cAMP determines the effect of CAP on lac operon transcription. presence of glucose inhibits the formation of cAMP and prevents it to bind to CAP
When this is on the operator the genes are off?
When a mutation is on the operator a gene can die which leads to an evolution of the entire genetic makeup. Also when lactose is absent and the genes should be switched off.
What is the act of Binding or tying off blood vessals or ducts?
Ligature
What is a repressible operon?
is one that is usually on; binding of a repressor to the operator shuts off transcription
A lac repressor turns off the lac genes by binding to?
When the lac repressor binds to the O region, RNA polymerase is prevented from beginning the process of transcription. In effect, the binding of the repressor protein turns the operon "off" by preventing the transcription of its genes. (Prentice Hall Biology Book .....Chapter 12 page 310)
A lac repressor turns ff the lac genes by binding to?
A lac repressor turns off the lac genes by binding to the operator
What causes the lac genes in E. coli to turn off?
A lac repressor turns off the lac genes by binding to the operator.
What Piece of DNA that serves as an on-off switch for transcription?
The operator
What is the operon hypothesis and discuss how it explains the control of?
control of messenger RNA production? An operon is made up of a promoter, structural genes, and the operator. The operator is basically the on-off switch for DNA polymerase. Transcription relies on the cell's regulator, which codes for a repressor that bind to the operator. When the repressor binds to the operator, the promoter is blocked. Thus, preventing transcription to occur. However, an inducer can activate or deactivate the repressor. When deactivated, RNA polymerase can bind to the DNA molecule to begin transcription.
In E. coli the tryprophan switches off the trp operon by?
Binding to the repressor and increasing the latter's affinity for the operator
How do repressors affect promoters?
a repressor is a protein that binds to DNA, which turns off the genes that code for the digestive enzymes. the promoter, located near the digestive enzyme genes, is a section on DNA that serves as the binding site for the enzyme RNA polymers.
Why is the tryptophan operon turned off in the presence of tryptophan?
Tryptophan binds to and activates the repressor proteins; the repressor proteins, in turn, bind to the operator, preventing transcription.
How do cells control gene expression?
The promoter allows the gene to be transcribed. It helps RNA polymerase find where a gene starts. An operator is a DNA segment that turns the gene "on" or "off." It interacts with proteins that increase the rate of transcription or block transcription from occurring.
What is the purpose is the safety lanyard on a personal watercraft?
If the operator falls into the water a lanyard between operator and a switch turns the engine off. If engine continued to run the operator would be stranded, the craft would continue uncontrolled perhaps causing damage to other craft, structures, or people; perhaps even running don the operator.
What is the purpose of having a safety lanyard on a personal watercraft?
If the operator falls into the water a lanyard between operator and a switch turns the engine off. If engine continued to run the operator would be stranded, the craft would continue uncontrolled perhaps causing damage to other craft, structures, or people; perhaps even running don the operator.
