Table of Contents
What does the lac repressor do?
The Lac repressor protein, LacI, prevents the transcription of genes involved in lactose utilization (lac genes) in E. coli. Like many other repressors, LacI utilizes multiple operators to increase the efficiency of repression.
What happens to the lactose repressor when lactose is present quizlet?
If lactose is present, it binds to and inactivates the repressor by causing it to fall off the operator.
How does the lac repressor regulate the lac operon quizlet?
How is the lac operon regulated? The lac operon is regulated by specific protein which turn it on when it is an environment where the food source is lactose, it would begin to turn the lactose into digestible galactose and glucose.
What happens in the presence of lactose quizlet?
In the presence of lactose allolactose goes and binds at the allosteric site of the repressor protein changing its shape which doesn’t allow the repressor protein to bind to the lac operator and the RNA polymerase transcribes the proteins.
What happens when the lactose binds with the repressor?
The lac repressor has a high affinity for lactose. When a small amount of lactose is present the lac repressor will bind it causing dissociation from the DNA operator thus freeing the operon for gene expression.
What does a lac repressor contain?
Structurally, the lac repressor protein is a homotetramer. More precisely, the tetramer contains two DNA-binding subunits composed of two monomers each (a dimer of dimers). Each monomer consists of four distinct regions: An N-terminal DNA-binding domain (in which two LacI proteins bind a single operator site)
When lactose is present what happens to the repressor?
When lactose is present, the lac repressor loses its DNA-binding ability. This clears the way for RNA polymerase to bind to the promoter and transcribe the lac operon.
How does lactose affect the lac operon quizlet?
How does the presence of lactose affect the lac operon? Lactose binds to the repressor protein, causing it to change shape and be unable to bind to the operator.
What do repressor proteins do?
Repressors are proteins that turn off or reduce gene expression, which is reflected by reduced messenger RNA production from the affected gene. Repressor proteins typically function through binding and blocking critical DNA sequences in the gene, such as the promoter where mRNA transcription starts.
How does the lac repressor bind to DNA?
The lac repressor (LacI) operates by a helix-turn-helix motif in its DNA-binding domain, binding base-specifically to the major groove of the operator region of the lac operon, with base contacts also made by residues of symmetry-related alpha helices, the “hinge” helices, which bind deeply in the minor groove.
What happens when the lactose is used up?
Lactase breaks down the lactose in food so your body can absorb it. People who are lactose intolerant have unpleasant symptoms after eating or drinking milk or milk products. These symptoms include bloating, diarrhea and gas.
What does the repressor protein do?
Repressor. Repressors are proteins that turn off or reduce gene expression, which is reflected by reduced messenger RNA production from the affected gene. Repressor proteins typically function through binding and blocking critical DNA sequences in the gene, such as the promoter where mRNA transcription starts.
When lactose is present the repressor protein?
If lactose is absent and glucose is present (see Fig. 16-13A), the gene products from the lac operon are not needed. Thus a regulatory factor, the repressor protein, prevents lac operon expression.
What is the function of a repressor protein quizlet?
A repressor is a type of protein that inactivates the expression of the lac operon genes by binding to the DNA of the lac operon. The lac operon in E. coli controls the gene expression of the enzymes that digest lactose in the cell. In the presence of lactose the lac operon will turn on and the genes will be expressed.
Where does the lac repressor bind?
upstream cis-activated operator
The lac repressor, which is constitutively expressed, binds to an upstream cis-activated operator and consequently blocks transcription of the genes necessary for the cell to utilize lactose as an energy source.
What is the enzyme that breaks down lactose?
lactase
Lactose intolerance happens when your small intestine does not make enough of a digestive enzyme called lactase. Lactase breaks down the lactose in food so your body can absorb it.