Chapter 23: Problem 32

Will an amino acid be glucogenic or ketogenic if it is catabolized to the following molecules? (a) Phosphoenolpyruvate (b) \(\alpha\) -Ketoglutarate (c) Succinyl-CoA (d) Acetyl-CoA (e) Oxaloacetate (f) Acetoacetate

Short Answer

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(a) Glucogenic (b) Glucogenic (c) Glucogenic (d) Ketogenic (e) Glucogenic (f) Ketogenic

Step by step solution

- Understanding Glucogenic and Ketogenic Amino Acids

Amino acids are classified based on the end products of their catabolism. Glucogenic amino acids are those that can be converted into glucose through gluconeogenesis, typically yielding pyruvate or intermediates of the citric acid cycle, which can then lead to glucose production. Ketogenic amino acids are those that yield acetyl-CoA or acetoacetate, which can go on to form ketone bodies.

- Phosphoenolpyruvate (PEP)

Phosphoenolpyruvate is an intermediate in the process of gluconeogenesis and glycolysis. Since it can eventually be converted into glucose, an amino acid catabolized to phosphoenolpyruvate is glucogenic.

- \( \alpha \) -Ketoglutarate

Alpha-Ketoglutarate is an intermediate in the citric acid cycle. Since intermediates of the citric acid cycle can be used for gluconeogenesis, an amino acid catabolized to alpha-ketoglutarate is glucogenic.

- Succinyl-CoA

Succinyl-CoA is another intermediate of the citric acid cycle. Therefore, an amino acid catabolized to succinyl-CoA is also classified as glucogenic.

- Acetyl-CoA

Acetyl-CoA is a precursor for ketone body synthesis and cannot be converted into pyruvate or intermediates of the citric acid cycle that can be used for gluconeogenesis. Therefore, an amino acid catabolized to acetyl-CoA is ketogenic.

- Oxaloacetate

Oxaloacetate is an intermediate in the citric acid cycle and a key substrate for gluconeogenesis. An amino acid catabolized to oxaloacetate is glucogenic.

- Acetoacetate

Acetoacetate is one of the ketone bodies. An amino acid catabolized to acetoacetate is classified as ketogenic.

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Key Concepts

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

amino acid catabolism

Amino acids are the building blocks of proteins, and they serve various functions in the body. When the body no longer needs them for building proteins, they undergo catabolism. Catabolism refers to the process of breaking down these amino acids for energy or other purposes. Some amino acids break down into products that can generate glucose, while others form products that can lead to ketone bodies. This differentiation splits amino acids into two main categories: glucogenic and ketogenic.

gluconeogenesis

Gluconeogenesis is an essential metabolic pathway that allows the body to generate glucose from non-carbohydrate sources, such as glucogenic amino acids. This process is critical during periods of fasting or intense exercise when glucose levels are low. Key intermediates in gluconeogenesis include pyruvate, oxaloacetate, and phosphoenolpyruvate. For example, amino acids broken down into oxaloacetate or alpha-ketoglutarate can enter the gluconeogenesis pathway and help sustain blood glucose levels.

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. It plays a crucial role in the catabolism of carbohydrates, fats, and proteins. The intermediates of this cycle, such as alpha-ketoglutarate and succinyl-CoA, can be quite versatile. They can be used either in energy production or as substrates for gluconeogenesis, making the amino acids that break down into these intermediates glucogenic.

acetyl-CoA

Acetyl-CoA is a key molecule in metabolism and plays a significant role in both the citric acid cycle and the synthesis of fatty acids. Unlike other intermediates of the citric acid cycle, acetyl-CoA cannot be converted back into carbohydrates through gluconeogenesis. Instead, it is a precursor for the production of ketone bodies, which are used as an alternative energy source when glucose is sparse. Therefore, amino acids that break down into acetyl-CoA are considered ketogenic.

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Will an amino acid be glucogenic or ketogenic if it is catabolized to the following molecules? (a) Phosphoenolpyruvate (b) \(\alpha\) -Ketoglutarate (c) Succinyl-CoA (d) Acetyl-CoA (e) Oxaloacetate (f) Acetoacetate

Short Answer

Step by step solution

- Understanding Glucogenic and Ketogenic Amino Acids

- Phosphoenolpyruvate (PEP)

- \( \alpha \) -Ketoglutarate

- Succinyl-CoA

- Acetyl-CoA

- Oxaloacetate

- Acetoacetate

Key Concepts

amino acid catabolism

gluconeogenesis

citric acid cycle

acetyl-CoA

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