Which statement describes the first chemical reaction in the Krebs Cycle?

Question

Which statement describes the first chemical reaction in the Krebs Cycle?

A. Pyruvate is converted to lactic acid.
B. Pyruvate is converted to acetyl CoA.
C. Citric acid loses a molecule of carbon dioxide to form a five-carbon compound.
D. Acetyl CoA combines with a four-carbon compound to form citric acid.
E. A five-carbon compound releases a molecule of CO2 to form a four-carbon compound.

Answer 1

D. The first step of the Krebs cycle (aka Citric acid cycle), is Acetyl-CoA is converted into Citrate by the addition of Oxaloacetate with help of citrate synthase. Co-enzyme A is released in this step.

Answer 2

In step 1 of the Krebs cycle, the two-carbon compound, acetyl-S-CoA, participates in a condensation reaction with the four-carbon compound, oxaloacetate, to produce citrate: The answer is D.

This reacion is moderately exergonic. Thermodynamically, the equilibrium is in favor of the products. Thus, this is considered to be the first committed step of the Krebs cycle
Being the first committed step, this is a likely step to have some kind of regulatory control mechanism (which will effectively regulate the entire cycle)
The Krebs cycle is also known as the citric acid cycle. Citrate is a tricarboxylic acid, and the Krebs cycle is also known as the tricarboxylic acid (or TCA) cycle

Answer 3

First Step Of Krebs Cycle

Answer 4

The citric acid cycle begins with the oxidation of pyruvate (to Acetyl-CoA) produced during glycolysis.

At least, that's what Wikipedia says...

(Do you trust them?)

Answer 5

D

Answer 6

D