Carbamoyl phosphate

Carbamoyl phosphate.

When amino acids are used for energy, their carbon skeletons are transformed by a variety of pathways into acetyl CoA or intermediates of glycolysis or the citric acid cycle. While the degradative pathways of some amino acids are complex and beyond the scope of the MCAT, the simpler transaminase pathways are within the scope of study. It is very good to have a general sense of this subject even though you don't need to memorize all six steps in the breakdown of leucine.

One very important topic is the fate of α-amine group when the breakdown of an amino acid occurs. As a general rule these amine groups will be converted into urea and then excreted. The pathway by which this occurs is called the urea cycle. The urea cycle takes place primarily in the liver, and to a lesser extent in the kidney. It was the first metabolic cycle discovered (Hans Krebs and Kurt Henseleit, 1932), five years before the discovery of the citric acid cycle.

WikiPremed Resources

Learning Goals

Proficiency 

Be prepared to describe the roles of transaminase and glutamate dehydrogenase in funneling nitrogen from amino acid degradation to the urea cycle.

Understand how the coenzyme pyridoxal phosphate assists in the transaminase mechanism.

Be able to name the reagents and products of the carbamoyl phosphate synthetase reaction.

Know the steps of the urea cycle.

Comprehend how the urea cycle is linked to the citric acid cycle through the output of fumarate and the return of aspartate.

Possess a sense of what factors (metabolic entry points) determine whether an amino acid is glucogenic, ketogenic, or both.

Suggested Assignments

The question server contains a general section covering basic concepts from gluconeogenesis, the pentose phosphate pathway, glyocogen metabolism, fatty acid metabolism, the urea cycle, and metabolic integration. After review complete the crossword puzzle for energy metabolism. Here is the solution to the puzzle.

Read pg. 75 in ExamKrackers Biology I.

Review the web resources for amino acid degradation and the urea cycle.

Conceptual Vocabulary for Amino Acid Degradation and the Urea Cycle