Which one of the following statements is true of enzyme catalysts? A. They bind

Question

Which one of the following statements is true of enzyme catalysts?

A. They bind to substrates, but are never covalently attached to substrate or product.

B. They increase the equilibrium constant for a reaction, thus favoring product formation

C. They increase the stability of the product of a desired reaction by allowing ionizations, resonance, and isomerizations not normally available to substrates

D. They lower the activation energy for the conversion of substrate to product

E. To be effective they must be present at the same concentration as their substrates

Explanation / Answer

The answer is , D. They lower the activation energy for the conversion of substrate to product

Enzymes do reduce activation energy like chemical catalysts. For example, activation energy for hydrolysis of sucrose using an acid is 6.22 kJ mol-1 but when sucrose is hydrolysed by enzyme sucrase, the activation energy is 2.15kJ mol-1.

Statements A, B, C and E are false.

A is wrong since covalent binding of enzyme to substrate is also known.

B is wrong since equilibrium constant is never affected by enzyme catalyst or chemical catalyst.

C is wrong since enzymes act as catalysts by a path which decreases activation energy and do not influence product stability.

E. is wrong is because like chemical catalysts, enzymes are required only in small quantities.

The answer is , D. They lower the activation energy for the conversion of substrate to product

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