Video Transcript
In eukaryotes, what cellular organelle is the site of the link reaction and Krebs
cycle?
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 cellular organelle that is the site of the link
reaction and Krebs cycle. To work out the answer, let’s first summarize the stages of respiration and where
they occur.
Glycolysis is the first stage of cellular respiration and 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.
The next stage of cellular respiration is the link reaction, which takes place in the
mitochondria. The pyruvate produced during glycolysis moves into the mitochondria, where it becomes
the reactant for the link reaction. As there are two molecules of pyruvate produced during glycolysis, there are two link
reactions for each molecule of glucose. The product of the link reaction is acetyl coenzyme A, which then enters the third
stage of cellular respiration, the Krebs cycle.
Like the link reaction, the Krebs cycle takes place in the mitochondria. As mentioned, the acetyl coenzyme A produced in the link reaction enters the Krebs
cycle, where it joins with a four-carbon compound called oxaloacetic acid to form
the six-carbon compound citric acid. A series of reactions take place during the Krebs cycle, producing a range of
products, including reduced NAD and FAD, which are particularly important for the
final stage of respiration, oxidative phosphorylation.
We now have enough information to answer our question. We have just seen how both the link reaction and the Krebs cycle take place in the
mitochondria. So the correct answer to the question “In eukaryotes, what cellular organelle is the
site of the link reaction and Krebs cycle?” is mitochondria.
