Urea Cycle Overview

Urea Cycle Overview

The urea cycle (also known as the ornithine cycle) is a metabolic pathway that occurs in the liver and kidneys. It is the primary mechanism by which the body disposes of excess ammonia, a toxic waste product.

Location and Importance

• Takes place in the liver and kidneys
• Essential for removing ammonia from the body, which is toxic to the brain and other organs

Reactions and Enzymes

The urea cycle consists of five reactions, catalyzed by five enzymes:

1. CPSI (Carbamoyl Phosphate Synthase I): converts ammonia and CO2 into carbamoyl phosphate
2. OTC (Ornithine Transcarbamylase): converts carbamoyl phosphate and ornithine into citrulline
3. ASS (Argininosuccinate Synthase): converts citrulline and aspartate into argininosuccinate
4. ASL (Argininosuccinate Lyase): converts argininosuccinate into arginine and fumarate
5. ARG (Arginase): converts arginine into ornithine and urea

Regulation

• The urea cycle is regulated by N-acetylglutamate, which is an allosteric activator of CPSI
• The cycle is also regulated by the availability of substrates, such as ammonia and aspartate

Defects and Disorders

• Defects in the urea cycle can lead to hyperammonemia, a condition characterized by elevated ammonia levels in the blood
• Symptoms of hyperammonemia include vomiting, lethargy, and seizures
• Inherited disorders of the urea cycle include CPSI deficiency, OTC deficiency, and ARG deficiency

Urea Cycle Overview

• The urea cycle is a metabolic pathway that occurs in the liver and kidneys to dispose of excess ammonia, a toxic waste product.

Location and Importance

• The urea cycle takes place in the liver and kidneys.
• It is essential for removing ammonia from the body, which is toxic to the brain and other organs.

Reactions and Enzymes

• The urea cycle consists of five reactions catalyzed by five enzymes.
• CPSI converts ammonia and CO2 into carbamoyl phosphate.
• OTC converts carbamoyl phosphate and ornithine into citrulline.
• ASS converts citrulline and aspartate into argininosuccinate.
• ASL converts argininosuccinate into arginine and fumarate.
• ARG converts arginine into ornithine and urea.

Regulation

• N-acetylglutamate is an allosteric activator of CPSI.
• The urea cycle is regulated by the availability of substrates, such as ammonia and aspartate.

Defects and Disorders

• Defects in the urea cycle can lead to hyperammonemia, a condition characterized by elevated ammonia levels in the blood.
• Symptoms of hyperammonemia include vomiting, lethargy, and seizures.
• Inherited disorders of the urea cycle include CPSI deficiency, OTC deficiency, and ARG deficiency.

Learn about the urea cycle, a metabolic pathway that occurs in the liver and kidneys, responsible for removing excess ammonia from the body.