12-6 Link Reaction (Cambridge AS A Level Biology, 9700)

Summary

The video explains the process following glycolysis, known as the link reaction. After glycolysis, pyruvate molecules are transported into the mitochondrial matrix, where they undergo decarboxylation (removal of carbon dioxide) and oxidation (removal of hydrogen). The hydrogen is accepted by NAD, forming reduced NAD. The remaining two-carbon molecule, the acetyl group, combines with coenzyme A (derived from vitamin B5) to form acetyl CoA, which enters the citric acid (Krebs) cycle. The process repeats for two pyruvate molecules, producing two acetyl CoA, two carbon dioxide molecules, and two reduced NAD molecules.

Takeaways

• 🧪 Glycolysis results in two pyruvate molecules, two reduced NAD molecules, and four ATP molecules.
• 🚶‍♂️ Pyruvate needs to enter the mitochondrial matrix for the link reaction to occur.
• 🔗 The link reaction has three steps: decarboxylation, oxidation (dehydrogenation), and addition of coenzyme A.
• ⚛️ Decarboxylation removes one carbon from pyruvate, producing carbon dioxide.
• 💧 Dehydrogenation removes hydrogen, which is accepted by NAD, forming reduced NAD.
• 🧩 The remaining two-carbon molecule is called the acetyl group.
• 🔬 Coenzyme A is needed to transport the acetyl group into the Krebs cycle.
• 🍽️ Coenzyme A is derived from vitamin B5 in the diet.
• 🚗 The combination of the acetyl group and coenzyme A forms acetyl CoA, which can enter the Krebs cycle.
• 🔄 Each pyruvate produces one carbon dioxide, one reduced NAD, and one acetyl CoA during the link reaction.

Q & A

What happens at the end of glycolysis?

At the end of glycolysis, glucose is broken down into two pyruvate molecules, and the process produces two reduced NAD molecules and four ATP molecules.

Where does the link reaction take place?

The link reaction takes place in the matrix of the mitochondria.

How does the pyruvate molecule enter the mitochondrial matrix?

The pyruvate molecule is actively transported into the mitochondrial matrix for the link reaction to occur.

What are the three steps involved in the link reaction?

The three steps of the link reaction are decarboxylation (removal of carbon dioxide), oxidation (dehydrogenation), and the addition of coenzyme A.

What is decarboxylation in the link reaction?

Decarboxylation in the link reaction is the removal of one carbon from the pyruvate molecule in the form of carbon dioxide.

What happens during oxidation in the link reaction?

During oxidation (dehydrogenation), the two-carbon molecule loses hydrogen, which is accepted by NAD to form reduced NAD (also known as NADH).

What is the role of coenzyme A in the link reaction?

Coenzyme A is added to the two-carbon acetyl group to form acetyl CoA, which is then able to enter the Krebs cycle.

Where does coenzyme A come from?

Coenzyme A is derived from vitamin B5 in the diet, which the body converts into coenzyme A.

What is the significance of acetyl CoA?

Acetyl CoA is the molecule that enters the Krebs cycle, allowing the acetyl group to participate in further energy-producing reactions.

How many pyruvate molecules undergo the link reaction, and what are the final products?

Two pyruvate molecules undergo the link reaction, producing two carbon dioxide molecules, two reduced NAD molecules, and two acetyl CoA molecules.