What happens when lactose is absent in the lac operon?

What happens when lactose is absent in the lac operon?

When lactose is not available, the lac repressor binds tightly to the operator, preventing transcription by RNA polymerase. However, when lactose is present, the lac repressor loses its ability to bind DNA. It floats off the operator, clearing the way for RNA polymerase to transcribe the operon.

How does beta galactosidase react with lactose?

β-Galactosidase has three enzymatic activities (Fig. 1). First, it can cleave the disaccharide lactose to form glucose and galactose, which can then enter glycolysis. The enzyme can hydrolyze lactose to galactose plus glucose, it can transgalactosylate to form allolactose, and it can hydrolyze allolactose.

What happens to the expression of the LACZ gene If lactose is not available in the cell?

What happens to the expression of the lacI gene if lactose is not available in the cell? There is no change—the lacI gene is constitutively expressed. The lacI gene turns off.

Why is lactose called an inducer?

The three structural genes are expressed as three enzymes to metabolise lactose to galactose and glucose. Lactose, thus, acts as the inducer for its own breakdown. Lactose binds with the repressor gene and inactivates ,it such that it can no longer bind to operator gene to stop it.

Why do some hormones require a second messenger?

Second Messenger Systems are called that because the hormone (the 1st messenger) doesn’t enter the cell (too big, usually) but initiates production of a chemical messenger within the cell (second messenger). The hormone binds to a receptor protein imbedded in the cell membrane.

Can testosterone diffuse through the membrane?

Testosterone is produced in the testes and travels through the blood in carrier proteins such as serum albumin or sex hormone binding globulin. It passively diffuses through the cell membranes of target cells.

Can steroid hormones diffuse through membrane?

Steroid hormones are generally thought to pass easily across a plasma membrane into a cell, interacting once inside with soluble nuclear receptors, but recent experiments have demonstrated the importance of membrane-bound receptors in mediating the activity and the metabolism of steroid hormones.

Can protein hormones pass through cell membrane?

They are water-soluble but cannot pass through the plasma membrane alone. Glyco-protein hormones have a carbohydrate moiety attached to the protein. Lipid hormones include steroid and eicosanoid hormones. They are lipid-soluble and can pass through the plasma membrane.