Question

Match the following ATP yields to reactions \(\mathbf{a}-\mathbf{g}\) : \(\begin{array}{llll}2 \text { ATP } & \text { 3 ATP } & \text { 6ATP } & \text { 12 ATP }\end{array}\) \(\begin{array}{lll}\text { 18 ATP } & \text { 36 ATP } & \text { 44 ATP }\end{array}\) a. Glucose forms two pyruvates. b. Pyruvate forms acetyl CoA. c. Glucose forms two acetyl CoAs. d. Acetyl CoA goes through one turn of the citric acid cycle. e. Caproic acid \(\left(\mathrm{C}_{6}\right)\) is completely oxidized. f. \(\mathrm{NADH}+\mathrm{H}^{+}\) is oxidized to \(\mathrm{NAD}^{+}\). g. FADH \(_{2}\) is oxidized to FAD.

Short answer

a-2, b-3, c-6, d-12, e-44, f-3, g-2

Step-by-step solution

- Match Glucose forming two pyruvates

Glucose forming two pyruvates yields 2 ATP. Therefore, match 2 ATP to reaction a.

- Match Pyruvate forming acetyl CoA

When pyruvate is converted to acetyl CoA, no direct ATP is produced. However, it produces NADH which yields 3 ATP when oxidized. Therefore, match 3 ATP to reaction b.

- Match Glucose forming two acetyl CoAs

Glucose forming two acetyl CoAs yields 2 pyruvates, each generating 1 NADH. Total yield is 2 NADH which is equivalent to 6 ATP. Therefore, match 6 ATP to reaction c.

- Match Acetyl CoA going through one turn of the citric acid cycle

Each turn of the citric acid cycle yields 1 ATP, 3 NADH (equivalent to 9 ATP), and 1 FADH2 (equivalent to 2 ATP). In total, it generates 12 ATP. Therefore, match 12 ATP to reaction d.

- Match Caproic acid (C6) being completely oxidized

The complete oxidation of a six-carbon fatty acid like caproic acid will go through multiple cycles and produce 44 ATP in total. Therefore, match 44 ATP to reaction e.

- Match NADH + H+ being oxidized to NAD+

One NADH + H+ yields 3 ATP when oxidized. Therefore, match 3 ATP to reaction f.

- Match FADH2 being oxidized to FAD

One FADH2 yields 2 ATP when oxidized. Therefore, match 2 ATP to reaction g.

Key concepts

glycolysis

Glycolysis is the first step of cellular respiration and occurs in the cytoplasm. It involves breaking down one molecule of glucose (6 carbons) into two molecules of pyruvate (3 carbons each). This process generates a net gain of 2 ATP molecules and 2 NADH molecules. Here's how it works in steps:

• Glucose is phosphorylated to form glucose-6-phosphate.
• It undergoes a series of transformations to become fructose-1,6-bisphosphate.
• This molecule splits into two 3-carbon molecules: glyceraldehyde-3-phosphate (G3P).
• Through oxidation and rearrangement, G3P gets converted into pyruvate, producing a net gain of 2 ATP and 2 NADH.

Glycolysis is essential because it doesn't require oxygen (anaerobic process). In the exercise, we matched glycolysis with yielding 2 ATP.

citric acid cycle

The citric acid cycle, also known as the Krebs cycle, occurs in the mitochondria. It plays a key role in energy production by oxidizing acetyl CoA to carbon dioxide and transferring energy to NADH and FADH2. Each turn of the cycle processes one acetyl CoA and yields:

• 1 ATP
• 3 NADH (equivalent to 9 ATP)
• 1 FADH2 (equivalent to 2 ATP)

Making a total of 12 ATP equivalents per turn. The citric acid cycle progresses as follows:

• Acetyl CoA combines with oxaloacetate to form citrate.
• Citrate undergoes a series of transformations losing two CO2 molecules, regenerating oxaloacetate.

During the exercise, this process was matched with 12 ATP.

oxidative phosphorylation

Oxidative phosphorylation takes place in the inner mitochondrial membrane and is the final step of cellular respiration. It involves the electron transport chain (ETC) and ATP synthase. Here’s how it works:

• NADH and FADH2 donate electrons to the ETC, which moves protons (H+) across the membrane.
• This creates a proton gradient, powering ATP synthase to produce ATP from ADP.
• Oxygen, the final electron acceptor, combines with protons to form water.

Oxidative phosphorylation is highly efficient and accounts for approximately 34 of the 36-38 total ATP produced from one molecule of glucose. In the exercise context:

• NADH yields 3 ATP when oxidized.
• FADH2 yields 2 ATP when oxidized.

These yield matches were specifically noted for NADH (3 ATP) and FADH2 (2 ATP).

metabolism

Metabolism encompasses all chemical reactions that occur within cells to maintain life. These reactions are divided into two categories: catabolism and anabolism.

• Catabolism breaks down molecules to produce energy. Key processes include glycolysis, the citric acid cycle, and oxidative phosphorylation.
• Anabolism builds up molecules like proteins and nucleic acids from smaller units using energy.

Integrating the whole concept, metabolism ensures that cells have the energy needed for various functions. The ATP yield from glucose metabolism demonstrates how these processes convert energy stored in food into usable ATP. For example, the complete oxidation of glucose yields 36-38 ATP. Each step of metabolism, such as glycolysis (2 ATP), conversion of pyruvate to acetyl CoA (3 ATP via NADH), the citric acid cycle (12 ATP per turn), and more, contributes to this total ATP production.