Question

Like Watson and Holmes. Match each term with its description. (a) Acetyl CoA (b) Citric acid cycle (c) Pyruvate dehydrogenase complex (d) Thiamine pyrophosphate (e) Lipoic acid (f) Pyruvate dehydrogenase (g) Acetyllipoamide (h) Dihydrolipoyl transacetylase (i) Dihydrolipoyl dehydrogenase (j) Beriberi 1\. Catalyzes the link between glycolysis and the citric acid cycle 2\. Coenzyme required by transacetylase 3\. Final product of pyruvate dehydrogenase 4\. Catalyzes the formation of acetyl CoA 5\. Regenerates active transacetylase 6\. Fuel for the citric acid cycle 7\. Coenzyme required by pyruvate dehydrogenase 8\. Catalyzes the oxidative decarboxylation of pyruvate 9\. Due to a deficiency of thiamine

Short answer

(c)-1, (e)-2, (a)-3, (f)-4, (i)-5, (a)-6, (d)-7, (f)-8, (j)-9.

Step-by-step solution

Identify Terms and Descriptions

Let's begin by listing the terms and their corresponding descriptions: (a) Acetyl CoA (b) Citric acid cycle (c) Pyruvate dehydrogenase complex (d) Thiamine pyrophosphate (e) Lipoic acid (f) Pyruvate dehydrogenase (g) Acetyllipoamide (h) Dihydrolipoyl transacetylase (i) Dihydrolipoyl dehydrogenase (j) Beriberi 1. Catalyzes the link between glycolysis and the citric acid cycle 2. Coenzyme required by transacetylase 3. Final product of pyruvate dehydrogenase 4. Catalyzes the formation of acetyl CoA 5. Regenerates active transacetylase 6. Fuel for the citric acid cycle 7. Coenzyme required by pyruvate dehydrogenase 8. Catalyzes the oxidative decarboxylation of pyruvate 9. Due to a deficiency of thiamine.

Match Descriptions 1 and 8

To find the catalyzing link between glycolysis and the citric acid cycle (description 1), we focus on processes that bridge glycolysis to the cycle. The "Pyruvate dehydrogenase complex" (c) catalyzes this step, connecting pyruvate to acetyl CoA formation. Therefore, (c) matches description 1. Description 8 involves the oxidative decarboxylation of pyruvate, a function of "Pyruvate dehydrogenase" (f). Therefore, (f) matches description 8.

Match Description 6

The fuel for the citric acid cycle (description 6) is "Acetyl CoA" (a), which directly enters the cycle. Therefore, (a) matches description 6.

Match Descriptions 3, 4, and 7

The final product of pyruvate dehydrogenase (description 3) is "Acetyl CoA" (a), matched above. Therefore, it's confirmed (a) matches description 3. Involved in the formation of acetyl CoA (description 4), "Pyruvate dehydrogenase" (f) catalyzes its production directly from pyruvate. Pyruvate dehydrogenase requires "Thiamine pyrophosphate" (d) as a coenzyme, therefore (d) matches description 7.

Match Descriptions 2 and 5

The coenzyme required by transacetylase (description 2) is "Lipoic acid" (e), utilized during enzymatic processes to convert substrates. Description 5 pertains to the regeneration of active transacetylase, handled by "Dihydrolipoyl dehydrogenase" (i), ensuring the enzyme remains in its functional state.

Match Descriptions 9

A deficiency of "Thiamine" results in "Beriberi" (j), a disease condition related to thiamine deficiency, hence (j) matches description 9.

Key concepts

Acetyl CoA

Acetyl CoA is a crucial molecule in metabolism. It serves as the primary fuel for the citric acid cycle, also known as the Krebs cycle. This compound is formed when the pyruvate dehydrogenase complex, a series of enzymes, converts pyruvate into acetyl CoA during the transition from glycolysis to the citric acid cycle.
This transformation is vital, as it helps to funnel the energy contained within carbohydrates into a form that the citric acid cycle can use. The process generates high-energy molecules, like ATP, that the cell can utilize for energy-requiring reactions. Essentially, acetyl CoA acts as a critical junction in the energy flow of the cell, determining whether to store energy, convert it to ATP, or use it for biosynthesis.

Citric Acid Cycle

The citric acid cycle is a central part of cellular metabolism and takes place in the mitochondria. Once acetyl CoA enters the cycle, it undergoes a series of reactions that release stored energy through the oxidation of these compounds. This results in the reduction of NAD extsuperscript{+} and FAD to NADH and FADH extsubscript{2}, as well as the production of ATP and carbon dioxide.
Each turn of the cycle processes one molecule of acetyl CoA, releasing two molecules of CO extsubscript{2} and transferring energy to electron carriers. These carriers then move to the electron transport chain, where further ATP generation occurs. It is called a "cycle" due to the regeneration of the starting molecule, oxaloacetate, at the end of every turn, ready to begin the process again with a new acetyl CoA.

Pyruvate Dehydrogenase Complex

The pyruvate dehydrogenase complex (PDC) is an essential group of enzymes that catalyze the conversion of pyruvate to acetyl CoA. This step acts as a critical gateway between the breakdown of glucose (glycolysis) and the full oxidation of glucose in the citric acid cycle.
The PDC consists of three catalytic components:

• Pyruvate dehydrogenase (E1), which decarboxylates pyruvate, releasing carbon dioxide.
• Dihydrolipoyl transacetylase (E2), transferring the resultant acetyl group to CoA.
• Dihydrolipoyl dehydrogenase (E3), regenerating NADH from NAD extsuperscript{+}.

This complex is tightly regulated. It is turned on or off in response to the cell’s energy needs, preventing unnecessary acetyl CoA production when energy supplies are adequate.

Thiamine Pyrophosphate

Thiamine pyrophosphate (TPP) is a critical coenzyme, required by several key enzymes in metabolism including the pyruvate dehydrogenase complex. Its primary role is to stabilize carbanion transition states and enable the decarboxylation of alpha-keto acids, like those in glucose metabolism.
In the context of the PDC, TPP is essential for catalyzing the decarboxylation of pyruvate by Pyruvate dehydrogenase (E1). Without adequate levels of this coenzyme, the entire metabolic process would slow down, leading to less acetyl CoA and therefore decreased energy production for the cell. This dependency underlines the importance of dietary thiamine (vitamin B1), the precursor of TPP, for maintaining efficient energy production and overall metabolic health.