Question

Describe how pyruvate is converted into a substance that enters the Krebs cycle. (2)

a) Pyruvate is directly converted into ATP.
b) Pyruvate is transformed into glucose.
c) Pyruvate is converted into acetyl-CoA, which enters the Krebs cycle.
d) Pyruvate is broken down into oxygen.

Answer 1

Pyruvate is converted into acetyl CoA by the enzyme pyruvate dehydrogenase, releasing CO2 and forming NADH in the process. This acetyl CoA then enters the Krebs cycle.

Step-by-step explanation:

In aerobic conditions, the conversion of pyruvate into a substance that can enter the Krebs cycle is an essential step for energy production in cells. This process occurs as follows:

• Pyruvate, produced during glycolysis, moves from the cytoplasm into the mitochondrial matrix.
• An enzyme called pyruvate dehydrogenase catalyzes the conversion of pyruvate into acetyl coenzyme A (acetyl CoA), which is an oxidative decarboxylation reaction.
• Carbon dioxide (CO2) is released and high-energy electrons are transferred to NAD+, forming NADH during this reaction.
• The two-carbon acetyl CoA then combines with a four-carbon molecule, oxaloacetate, to form the six-carbon molecule citrate, or citric acid, and enters the Krebs cycle (Citric Acid Cycle).

To summarize, the correct option for the initial question is (c): Pyruvate is converted into acetyl-CoA, which enters the Krebs cycle.