How does the activator protein control lac operon?
The activator protein CAP, when bound to a molecule called cAMP (discussed later), binds to the CAP binding site and promotes RNA polymerase binding to the promoter. The lac repressor protein binds to the operator and blocks RNA polymerase from binding to the promoter and transcribing the operon.
What would be the effect of a mutation in the operator that blocked the lac repressor binding?
b) Mutations in the repressor that prevent its binding to the operator will lead to constitutive expression (no repression in the absence of inducer). An “up” mutation would make the lac operon no longer dependent on the positive regulation by the cAMP‑CAP complex (when the operon is induced).
What happens when tryptophan is absent?
When tryptophan is absent, the repressor protein does not bind to the operator and the genes are transcribed. When tryptophan is present in the cell, two tryptophan molecules bind to the trp repressor, which changes shape to bind to the trp operator.
Does the activator bind to the operator?
Some genes are modulated by activators, which have the opposite effect on gene expression as repressors. Inducers can also bind to activator proteins, allowing them to bind to the operator DNA where they promote RNA transcription.
What is the function of catabolite activator protein?
Catabolite activator protein (CAP), also known as cyclic AMP receptor protein (CRP), is activated by cyclic AMP and stimulates synthesis of the enzymes that break down non-glucose food molecules.
How does mutation affect operon?
For example, mutations affecting the promoter can prevent all of the operon’s genes from being expressed, because RNA polymerase will be unable to bind and commence transcription. Other mutations may affect expression of only some of the genes in the operon.
How does glucose affect the lac operon?
Glucose therefore stops activation of the lac operon (a cluster of coordinately regulated genes involved in lactose catabolism), which prevents lactose use and leads to preferential use of glucose.
How do activators affect transcription?
Transcription factors are proteins that help turn specific genes “on” or “off” by binding to nearby DNA. Transcription factors that are activators boost a gene’s transcription. Groups of transcription factor binding sites called enhancers and silencers can turn a gene on/off in specific parts of the body.
How do activators affect enzymes?
Enzyme activators are chemical compounds that increase a velocity of enzymatic reaction. Their actions are opposite to the effect of enzyme inhibitors. Cations can bind not only with enzyme but also with the substrate increasing its affinity to the enzyme that activate enzyme.
What happens to the trp operon when tryptophan is absent?
These five genes are next to each other in what is called the tryptophan (trp) operon. This physically blocks the RNA polymerase from transcribing the tryptophan genes. When tryptophan is absent, the repressor protein does not bind to the operator and the genes are transcribed.
Which of the following takes place when tryptophan levels are low?
Explanation: Formation of the attenuator stem-and-loop structure depends on the events that occur during translation of regulatory sequence 1, which encodes a leader peptide. Explanation: b, c and d take place when tryptophan levels are low.
What are the two conditions for the lac operon to be expressed?
The lac operon will be expressed at high levels if two conditions are met: 1 Glucose must be unavailable: When glucose is unavailable, cAMP binds to CAP, making CAP able to bind DNA. Bound CAP… 2 Lactose must be available: If lactose is available, the lac repressor will be released from the operator (by binding of… More
What is the function of lac operon in E coli?
The lac operon of E. coli contains genes involved in lactose metabolism. It’s expressed only when lactose is present and glucose is absent. Two regulators turn the operon “on” and “off” in response to lactose and glucose levels: the lac repressor and catabolite activator protein (CAP). The lac repressor acts as a lactose sensor.
What happens when glucose is absent in the lac operon?
Glucose absent, lactose present: Strong transcription of the lac operon occurs. The lac repressor is released from the operator because the inducer (allolactose) is present. cAMP levels are high because glucose is absent, so CAP is active and bound to the DNA. CAP helps RNA polymerase bind to the promoter, permitting high levels of transcription.
What is the function of the lac repressor in lactose intolerance?
It’s expressed only when lactose is present and glucose is absent. Two regulators turn the operon “on” and “off” in response to lactose and glucose levels: the lac repressor and catabolite activator protein (CAP). The lac repressor acts as a lactose sensor.