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Chapter 21: Problem 3

Energy harvest. What is the yield of ATP when each of the following substrates is completely oxidized to \(\mathrm{CO}_{2}\) by a mammalian cell homogenate (p. 71)? Assume that glycolysis, the citric acid cycle, and oxidative phosphorylation are fully active. (a) Pyruvate (b) Lactate (c) Fructose 1,6 -bisphosphate (d) Phosphoenolpyruvate (e) Galactose (f) Dihydroxyacetone phosphate

Short Answer

Expert verified
a) 12.5 ATP b) 12.5 ATP c) 30 ATP d) 13.5 ATP e) 32 ATP f) 16 ATP

Step by step solution

01

Understand ATP Yield from Pyruvate

When pyruvate is completely oxidized to CO2, it undergoes conversion to acetyl-CoA, entering the citric acid cycle. This oxidation indirectly generates ATP via NADH and FADH2 as electron carriers. 1 pyruvate gives: - Pyruvate to Acetyl-CoA: 1 NADH (equivalent to 2.5 ATP) - Citric Acid Cycle: 3 NADH (7.5 ATP), 1 FADH2 (1.5 ATP), 1 GTP (1 ATP) Therefore, total ATP from 1 pyruvate: 12.5 ATP.
02

Calculate ATP Yield from Lactate

Lactate is first converted to pyruvate, yielding no direct ATP or NADH. Then, pyruvate goes through the same oxidation process as described in Step 1. Therefore, total ATP from 1 lactate: 12.5 ATP.
03

Determine ATP Yield from Fructose 1,6-bisphosphate

Fructose 1,6-bisphosphate enters glycolysis, converting to two molecules of glyceraldehyde 3-phosphate, then undergoing glycolysis to pyruvate. It yields: 1 Fructose 1,6-bisphosphate gives: - Glycolysis yields: 4 ATP (2 net ATP) and 4 NADH (5 ATP) for 2 Glyceraldehyde 3-phosphate - Pyruvate (from glycolysis) oxidized further (see Step 1): 2 pyruvate yield 2 x 12.5 ATP = 25 ATP Therefore, total ATP from 1 fructose 1,6-bisphosphate: 30 ATP.
04

Analyze ATP Yield from Phosphoenolpyruvate (PEP)

Phosphoenolpyruvate converts to pyruvate in glycolysis, contributing to net ATP and NADH. 1 Phosphoenolpyruvate gives: - 1 ATP directly from conversion to pyruvate - Pyruvate oxidized further (see Step 1), which gives 12.5 ATP Therefore, total ATP from 1 phosphoenolpyruvate: 13.5 ATP.
05

Identify ATP Yield from Galactose

Galactose enters glycolysis similar to glucose, converting to glucose 6-phosphate before proceeding through glycolysis. 1 Galactose yields: - Glycolysis yields: 2 net ATP and 2 NADH from the resulting glucose (5 ATP) - 2 Pyruvate generated earlier in glycolysis further oxidized (see Step 1): 2 x 12.5 ATP = 25 ATP Therefore, total ATP from 1 galactose: 32 ATP.
06

Evaluate ATP Yield from Dihydroxyacetone Phosphate (DHAP)

Dihydroxyacetone phosphate is an intermediary in glycolysis, converting to glyceraldehyde 3-phosphate, sharing the pathway towards generating pyruvate. 1 DHAP gives: - Forms glyceraldehyde 3-phosphate which yields 1 ATP and 1 NADH (2.5 ATP) - Yields 1 pyruvate further oxidized (see Step 1), contributing 12.5 ATP Therefore, total ATP from 1 dihydroxyacetone phosphate: 16 ATP.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Biochemical Pathways
Biochemical pathways refer to a series of chemical reactions occurring within a cell. These reactions lead to the conversion of one or more substrates into different products. In the context of ATP yield, pathways like glycolysis, the citric acid cycle, and oxidative phosphorylation are crucial.
  • Glycolysis: This is a pathway that breaks down glucose to pyruvate, producing a net gain of ATP and NADH. It's essential for energy production in cells.
  • Citric Acid Cycle: Also known as the Krebs cycle, this pathway further oxidizes acetyl-CoA, yielding ATP and other high-energy electron carriers.
  • Oxidative Phosphorylation: It involves the electron transport chain and uses the energy from electrons to form ATP.
These pathways are interconnected, where the output of one can feed into another, maintaining the cell鈥檚 energy balance. Understanding these pathways helps explain how cells manage energy efficiently.
Oxidative Phosphorylation
Oxidative phosphorylation is a critical process that occurs in the mitochondria. It generates the majority of ATP in aerobic organisms. This complex process involves several key components and functions to create a gradient used to produce ATP.
  • Electron Transport Chain (ETC): Electrons from NADH and FADH2 are transferred through a series of protein complexes in the mitochondrial membrane.
  • Proton Gradient: As electrons move through the ETC, protons are pumped across the membrane, creating a gradient.
  • ATP Synthase: The energy from the proton gradient drives ATP synthase to produce ATP from ADP and inorganic phosphate.
The complete oxidation of one molecule of glucose can result in approximately 34 ATP molecules through oxidative phosphorylation. It highlights how crucial this process is for energy yield.
Glycolysis
Glycolysis is the first step in the breakdown of glucose, occurring regardless of oxygen presence. It occurs in the cytosol and is vital for cellular respiration.
  • Initial Investment: Glycolysis consumes 2 ATP to start the breakdown process of glucose.
  • Energy Payoff: It produces 4 ATP and 2 NADH, making a net gain of 2 ATP per glucose molecule.
  • End Products: The main products are 2 molecules of pyruvate, which can then be used in anaerobic processes or further oxidized in the presence of oxygen.
Glycolysis plays a crucial role in cellular metabolism by providing intermediates for other pathways and serving as a primary energy source when oxygen is scarce.
Citric Acid Cycle
The citric acid cycle, also known as the Krebs cycle, is an essential metabolic pathway that occurs in the mitochondria. It follows glycolysis and is a central component of energy production.
  • Acetyl-CoA Entry: Pyruvate from glycolysis is converted to acetyl-CoA, which enters the cycle.
  • High-Energy Carriers: For each acetyl-CoA, the cycle produces 3 NADH, 1 FADH2, and 1 GTP (equivalent to ATP).
  • CO2 Release: Two molecules of carbon dioxide are released, completing the oxidation of acetyl groups.
The citric acid cycle is vital for extracting high-energy electrons used in oxidative phosphorylation to produce ATP. It's also crucial for other biosynthetic pathways in the cell.

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Most popular questions from this chapter

Currency exchange. For a proton-motive force of 0.2 \(\mathrm{V}\) (matrix negative), what is the maximum [ATP]/[ADP][P_i] ratio compatible with ATP synthesis? Calculate this ratio three times, assuming that the number of protons translocated per ATP formed is two, three, and four and that the temperature is \(25^{\circ} \mathrm{C} . \sqrt{3}\)

Runaway mitochondria 2. Years ago, it was suggested that uncouplers would make wonderful diet drugs. Explain why this idea was proposed and why it was rejected. Why might the producers of antiperspirants be supportive of the idea?

Mitochondrial disease. A mutation in a mitochondrial gene encoding a component of ATP synthase has been identified. People who have this mutation suffer from muscle weakness, ataxia (uncoordinated movement), and retinitis pigmentosa. A tissue biopsy was performed on each of three patients having this mutation, and submitochondrial particles were isolated that were capable of succinatesustained ATP synthesis. First, the activity of the ATP synthase was measured on the addition of succinate and the following results were obtained. (a) What was the purpose of the addition of succinate? (b) What is the effect of the mutation on succinate-coupled ATP synthesis? (c) Why was succinate omitted from the reaction? (d) What is the effect of the mutation on ATP hydrolysis? (e) What do these results, in conjunction with those obtained in the first experiment, tell you about the nature of the mutation?TABLES CANT COPY Next, the ATPase activity of the enzyme was measured by incubating the submitochondrial particles with ATP in the absence of succinate.

Alternative routes. The most common metabolic sign of mitochondrial disorders is lactic acidosis. Why?

Imposing a gradient. Mitoplasts are mitochondria that lack the outer membrane but are still capable of oxidative phosphorylation. Suppose that you were to soak mitoplasts in a pH 7 buffer for several hours. Then, you rapidly isolated the mitoplasts and mixed them in a pH 4 buffer containing ADP and \(P_{i}\). Would ATP synthesis take place? Explain.
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