Question Video: Recalling the Primary Reactant of the Link Reaction Biology

Video Transcript

The link reaction occurs in between glycolysis and the Krebs cycle. What is the primary reactant of the link reaction?

Cells perform cellular respiration in order to extract energy from sugar and transfer this energy to a molecule called ATP. Aerobic cellular respiration is a multistep process. These steps are glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation. The question asks us to identify the primary reactant of the link reaction. To work out the answer, let’s first summarize what happens in glycolysis, since the products of glycolysis will become the reactants in the link reaction.

Glycolysis takes place in the cytoplasm of the cell. During glycolysis, one molecule of glucose, the most common respiratory substrate, is converted through a series of reactions into two molecules of pyruvate. In our diagram, each carbon is represented by a circle. So you can see that glucose has six carbons, while the two pyruvate molecules produced each have three carbons.

The next stage in cellular respiration is the link reaction, which takes place in the mitochondria. The pyruvate produced during glycolysis is transported from the cytoplasm into the mitochondria. The pyruvate molecule then undergoes a series of changes during the link reaction. The product of the link reaction, acetyl coenzyme A, then enters the Krebs cycle, the third stage of cellular respiration.

Now that we have reviewed how the link reaction connects glycolysis and the Krebs cycle, let’s take another look at our question. We are asked, what is the primary reactant of the link reaction? We have just seen how the main product of glycolysis is pyruvate, which is transported into the mitochondria to be used in the link reaction. So the correct answer to “What is the primary reactant of the link reaction?” is pyruvate.