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Chapter 7: Problem 11

How many NADH molecules are produced on each turn of the citric acid cycle? a. one b. two c. three d. four

Short Answer

Expert verified
c. three

Step by step solution

01

Understand the Citric Acid Cycle

The citric acid cycle (also known as the Krebs cycle) is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins into carbon dioxide and water.
02

Identify the Key Steps Producing NADH

In the citric acid cycle, three specific steps involve the reduction of NAD+ to NADH: 1. Conversion of isocitrate to 伪-ketoglutarate by the enzyme isocitrate dehydrogenase 2. Conversion of 伪-ketoglutarate to succinyl-CoA by the enzyme 伪-ketoglutarate dehydrogenase3. Conversion of malate to oxaloacetate by the enzyme malate dehydrogenase
03

Count the Produced NADH Molecules

Each of these three steps produces one NADH molecule, resulting in a total of three NADH molecules being produced on each turn of the citric acid cycle.
04

Verify Answer Options

Given the information gathered, the correct answer must reflect that three NADH molecules are produced per cycle turn. Therefore, the answer is option c. three.

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Key Concepts

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

Krebs cycle
The Krebs cycle, also known as the citric acid cycle, is a fundamental part of cellular metabolism. It takes place in the mitochondria of cells. This cycle plays a crucial role in breaking down organic fuel molecules (like glucose, fats, and proteins) to produce energy. Each cycle begins with the combination of a four-carbon molecule called oxaloacetate and a two-carbon molecule from acetyl-CoA. Here's a simple breakdown of the steps involving NADH production:
  • Isocitrate is converted to 伪-ketoglutarate.
  • 伪-Ketoglutarate is converted to succinyl-CoA.
  • Malate is converted to oxaloacetate.
Each of these steps involves oxidation-reduction reactions, where NAD+ is reduced to NADH.
aerobic respiration
Aerobic respiration is a process that uses oxygen to generate energy from nutrients. This involves several stages: glycolysis, the Krebs cycle, and the electron transport chain.
Here's a quick summary of how it works:
  • Glycolysis occurs in the cytoplasm and breaks glucose down into pyruvate, producing a small amount of ATP and NADH.
  • The pyruvate then enters the mitochondria and is converted into acetyl-CoA, which enters the Krebs cycle.
  • The Krebs cycle generates more NADH and FADH2, as well as a small amount of ATP.
  • Finally, NADH and FADH2 transfer their electrons to the electron transport chain, creating a large amount of ATP through oxidative phosphorylation.
It鈥檚 called 'aerobic' because oxygen is the final electron acceptor in the electron transport chain. Without oxygen, this process cannot occur.
energy generation
Energy generation in cells is essential for maintaining all cellular functions. The main goal of processes like the Krebs cycle and aerobic respiration is to produce ATP, the energy currency of cells.
Here鈥檚 how energy is generated in these processes:
  • In the Krebs cycle, acetyl-CoA is oxidized, and high-energy molecules like NADH and FADH2 are produced.
  • NADH and FADH2 carry electrons to the electron transport chain in the inner mitochondrial membrane.
  • During oxidative phosphorylation, electrons move through the chain and help pump protons, creating a proton gradient.
  • This gradient generates a flow of protons back into the mitochondria through ATP synthase, converting ADP into ATP.
Ultimately, every NADH and FADH2 molecule generated in the Krebs cycle is crucial for ATP production, which powers virtually all cellular activities.

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Most popular questions from this chapter

E. coli are enteric (gut-dwelling) facultative anaerobic bacteria. (Facultative anaerobes can grow either with or without free oxygen. Obligatory anaerobes grow only in the absence of free oxygen.) Researchers planned to grow cultures of \(E .\) coli under a range of conditions to model the transition from strictly anaerobic to aerobic respiration. The oxygen content of atmospheres at constant total pressure will be controlled by volumes of nitrogen and oxygen gases. Ratios of volume, \(r=\mathrm{V}_{\mathrm{O}_{2}} / \mathrm{V}_{\mathrm{N}_{2}}\) between 0 and 0.25 of shaken growth flasks can be measured in terms of optical density, which is the percent of transmission of light through a sample of the growing \(E\) . coli culture. A rule of thumb is that the range of strict anaerobes is when r \(<0.01,\) and the boundary for aerobic respiration is when \(\mathrm{r}\) \(=0.05 .\) A large number of flasks that can be constantly shaken at fixed temperature, and from which samples can be taken without atmospheric contamination, are available for this study. These results of the experiment will be used to infer growth rates of \(E\) . coli along the entire 7.5 \(\mathrm{m}\) length of the average human intestine (small intestine and large intestine), where the oxygen content varies from atmospheric to anaerobic conditions. The retention time of food in the small intestine, whose average length is \(2.5 \mathrm{m},\) is approximately four hours. The retention time of food over the entire length of the intestine is between 24 and 72 hours. A. Describe and apply a mathematical model that can be used to represent the variation of oxygen environments of a bacterium that is being transported with the food along the length of the intestine. B. Design the experimental sampling times in terms of growth intervals of interest in this study: i) the time when the bacteria is passing the small-large intestine boundary; ii) the time when the bacteria reaches the end of the large intestine; and iii) the time when the bacterium reaches facultative anaerobic conditions, r \(<0.05 .\)C. C. Sketch a graph that predicts the distribution of aerobic, facultative anaerobic and obligatory anaerobic bacteria along the length of the entire intestine based on these parameters. Keep in mind that anaerobes have a lower respiration rate.

Nearly all organisms on earth carry out some form of glycolysis. How does this fact support or not support the assertion that glycolysis is one of the oldest metabolic pathways? a. To be present in so many different organisms, glycolysis was probably present in a common ancestor rather than evolving many separate times. b. Glycolysis is present in nearly all organisms because it is an advanced and recently evolved pathway that has been widely used as it is so beneficial. c. Glycolysis is absent in a few higher organisms. This contradicts the fact that it is one of the oldest metabolic pathways. d. Glycolysis is present in some organisms and absent in others. The mentioned fact may or may not support this assertion.

Which of the following molecules are oxidizing agents? a. \(\mathrm{FAD}^{+}\) and \(\mathrm{NAD}^{+}\) b. \(\mathrm{FADH}_{2}\) and \(\mathrm{NADH}\) c. FAD and \(\mathrm{FADH}_{2}\) d. \(\mathrm{NAD}^{+}\) and \(\mathrm{NADH}\)

What is the primary difference between fermentation and anaerobic respiration? a. Fermentation uses only glycolysis and its final electron acceptor is an organic molecule, whereas anaerobic respiration uses glycolysis, TCA and the ETC but finally give electrons to an inorganic molecule. b. Fermentation uses glycolysis, TCA and ETC but finally gives electrons to an inorganic molecule, whereas anaerobic respiration uses only glycolysis and its final electron acceptor is an organic molecule. c. Fermentation uses glycolysis and its final electron acceptor is an inorganic molecule, whereas anaerobic respiration uses glycolysis, TCA and ETC but finally give electrons to an organic molecule. d. Fermentation uses glycolysis, TCA and ETC but finally gives electrons to an organic molecule, whereas anaerobic respiration uses only glycolysis and its final electron acceptor is an inorganic molecule.

Cellular respiration breaks down glucose and releases carbon dioxide and water. Which steps in the oxidation of pyruvate produces carbon dioxide? a. Removal of a carboxyl group from pyruvate releases carbon dioxide. The pyruvate dehydrogenase complex comes into play. b. Removal of an acetyl group from pyruvate releases carbon dioxide. The pyruvate decarboxylase complex comes into play. c. Removal of a carbonyl group from pyruvate releases carbon dioxide. The pyruvate dehydrogenase complex comes into play. d. Removal of an acetyl group from pyruvate releases carbon dioxide. The pyruvate dehydrogenase complex comes into play
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