Practice: Amino Acid Oxidation 2 - Online Tutor, Practice Problems & Exam Prep

Amino acids can be classified as glucogenic or ketogenic, with all generating urea during metabolism. In the liver, glutamate undergoes oxidative deamination to form α-ketoglutarate. Glucogenic amino acids like serine, cysteine, and alanine are converted to pyruvate. Phenylketonuria arises from a defect in converting phenylalanine to tyrosine, leading to elevated phenylacetate levels in infants. Early dietary intervention is crucial to prevent neurological issues. Understanding these metabolic pathways is essential for grasping amino acid catabolism and its implications for health.

Practice

The amino acids from the previous question are both glucogenic and ketogenic. All amino acids will generate urea, and no amino acid is capable of directly interacting with complex 2 of the electron transport chain. That's the job of FAD. So, the answer to this question is all of the above.

Now, the cofactor required for all amino acid degradation pathways is the first transaminase. And in the liver mitochondria, glutamate is converted to alpha-ketoglutarate by a process that can be described as oxidative deamination.

The amino acids serine, cysteine, and alanine are catabolized to yield pyruvate, and these are glucogenic amino acids. Phenylketonuria, which is a genetic disease, can result from the inability to convert phenylalanine, and it's actually the first enzyme in this pathway. A defect in the first enzyme in this pathway that converts phenylalanine to tyrosine. So, babies are checked for certain compounds called phenylacetate, which is just a marker of the inability to convert phenylalanine to tyrosine. If they find phenylacetate in babies, they keep them on a low phenylalanine diet in the early years when their brains are still developing to prevent any problems.

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Here’s what students ask on this topic:

What are glucogenic and ketogenic amino acids?

Glucogenic amino acids are those that can be converted into glucose through gluconeogenesis. They are catabolized to intermediates like pyruvate or citric acid cycle intermediates. Examples include serine, cysteine, and alanine. Ketogenic amino acids, on the other hand, are those that can be converted into ketone bodies. They are catabolized to acetyl-CoA or acetoacetate. Some amino acids, like isoleucine and phenylalanine, are both glucogenic and ketogenic. Understanding these classifications is crucial for studying metabolic pathways and their implications for energy production and disease states.

What is the role of oxidative deamination in amino acid metabolism?

Oxidative deamination is a process where an amino acid, typically glutamate, loses an amino group to form α-ketoglutarate and ammonia. This reaction occurs in the liver mitochondria and is catalyzed by the enzyme glutamate dehydrogenase. The ammonia produced is then converted to urea in the urea cycle for excretion. This process is essential for the removal of excess nitrogen from the body and for the production of intermediates that enter the citric acid cycle, contributing to energy production.

How does phenylketonuria (PKU) affect amino acid metabolism?

Phenylketonuria (PKU) is a genetic disorder caused by a defect in the enzyme phenylalanine hydroxylase, which converts phenylalanine to tyrosine. This defect leads to the accumulation of phenylalanine and its byproducts, such as phenylacetate, in the body. High levels of phenylalanine can cause severe neurological damage, especially in developing infants. Early detection through newborn screening and dietary management with a low-phenylalanine diet are crucial to prevent cognitive impairment and other health issues associated with PKU.

Why are newborns screened for phenylketonuria (PKU)?

Newborns are screened for phenylketonuria (PKU) to detect the disorder early and prevent its severe consequences. PKU is caused by a defect in the enzyme phenylalanine hydroxylase, leading to the accumulation of phenylalanine and its toxic byproducts. High levels of phenylalanine can cause irreversible brain damage and cognitive impairment. Early detection allows for immediate dietary intervention, specifically a low-phenylalanine diet, which can prevent the neurological damage and allow for normal development. This screening is a critical public health measure to ensure the well-being of affected infants.

What is the significance of pyruvate in amino acid catabolism?

Pyruvate plays a crucial role in amino acid catabolism as it is a key intermediate in several metabolic pathways. Glucogenic amino acids like serine, cysteine, and alanine are catabolized to yield pyruvate. Pyruvate can then be converted into acetyl-CoA for entry into the citric acid cycle, or it can be used in gluconeogenesis to produce glucose. This versatility makes pyruvate a central molecule in energy production and metabolic regulation, linking amino acid catabolism to broader metabolic processes.