Which of the following is a term usually used to describe the type of ligand that binds enzymes and membrane transporters

Which of the following is a term usually used to describe the type of ligand that binds enzymes and membrane transporters?

1) reaction intermediate

2) substrate

3) reactant

4) regulatory protein

The correct answer and explanation is:

Correct Answer: 2) Substrate

Explanation:

In biochemistry and molecular biology, the term “substrate” is commonly used to describe the molecule that binds to an enzyme or membrane transporter and is acted upon in some way.

Understanding the Terms:

1. Substrate – A substrate is the specific reactant that binds to the active site of an enzyme or transporter protein. In the case of enzymes, the substrate undergoes a chemical transformation to become the product of the reaction. In transporters, the substrate is typically the molecule being moved across a membrane.
2. Reaction Intermediate – This refers to a short-lived molecule formed in the middle steps of a chemical reaction pathway. While important in the progression of reactions, intermediates are not the original molecules that bind enzymes.
3. Reactant – This is a more general term that refers to any starting material in a chemical reaction. While a substrate is a type of reactant, not all reactants are substrates. The term “substrate” is preferred when describing enzyme interactions.
4. Regulatory Protein – These proteins control the function of other proteins, often by binding to enzymes or DNA, but they are not substrates. Instead, they modulate activity, such as turning enzymes “on” or “off.”

Why “Substrate” is Correct:

• Enzyme Example: In the reaction catalyzed by the enzyme lactase, the sugar lactose is the substrate. Lactase binds lactose, breaks it down into glucose and galactose, and releases the products.
• Transporter Example: In glucose transporters like GLUT1, glucose acts as the substrate that is transported across the cell membrane.

Conclusion:

The term substrate is the most specific and accurate term for the molecule that binds to the active site of an enzyme or transporter and undergoes some kind of biochemical process. Therefore, option 2 is correct.