Optometry Admission Test (OAT) Practice

Which substance is produced in the liver when excess amino acids are broken down?

1. Glycogen

2. Glucose

3. Urea

4. Lactate

The correct answer is: Urea

When excess amino acids are broken down in the liver, the primary substance produced is urea. This process occurs through a series of reactions known as deamination, where the amino group is removed from the amino acids. The removal of the amino group results in the production of ammonia, a toxic compound. The liver then converts the ammonia into urea through the urea cycle, allowing it to be safely excreted by the kidneys in urine. The production of urea is a critical metabolic pathway because it helps to regulate nitrogen balance in the body and prevent toxicity from high levels of ammonia. This metabolic process is significant for maintaining homeostasis, particularly when protein intake is high or during periods of fasting when the body may need to utilize proteins for energy. This context is essential for understanding why the other substances mentioned, like glycogen, glucose, and lactate, are not produced directly from the breakdown of excess amino acids. Glycogen is a storage form of glucose, primarily generated from carbohydrate metabolism. Glucose itself can be synthesized through gluconeogenesis, but it is not the primary product of amino acid catabolism. Lactate is produced from anaerobic metabolism of glucose and is not directly related to the breakdown of amino acids.