Question

Which of these statements about lactate dehydrogenase is true? a. It is a protein. b. It oxidizes lactic acid. c. It reduces another molecule (pyruvic acid). d. All of these are true.

Short answer

All of the statements about lactate dehydrogenase are true: it is a protein, it oxidizes lactic acid, and it reduces another molecule (pyruvic acid). So, the correct answer is d. All of these are true.

Step-by-step solution

Statement a: "It is a protein."

Lactate dehydrogenase is an enzyme involved in the conversion of lactate to pyruvic acid, a key step in cellular metabolism. Enzymes are specialized proteins that act as biological catalysts, speeding up chemical reactions in cells. So, lactate dehydrogenase is a protein. Therefore, statement a is true.

Statement b: "It oxidizes lactic acid."

Lactate dehydrogenase indeed catalyzes the conversion of lactate to pyruvic acid. During this reaction, lactate is oxidized to pyruvic acid. In other words, lactate dehydrogenase oxidizes lactic acid. Therefore, statement b is true.

Statement c: "It reduces another molecule (pyruvic acid)."

The function of lactate dehydrogenase is to catalyze the reversible conversion of lactate to pyruvic acid. In one direction, the enzyme oxidizes lactate, and in the other direction, it reduces pyruvic acid back to lactate. So, lactate dehydrogenase reduces another molecule, i.e., pyruvic acid. Therefore, statement c is true.

Comparing all statements

Upon analyzing statements a, b, and c, we found that all of them are true. Therefore the correct answer to this question is: d. All of these are true.