What is the purpose of the urea cycle?
Table of Contents
- 1 What is the purpose of the urea cycle?
- 2 Why is it important for urea to be excreted?
- 3 What are the five main reactions involved in urea cycle?
- 4 What role does urea have in tubular reabsorption?
- 5 Which answer best describes the formation of urea in mammals?
- 6 What is the implication of urea formation during protein metabolism?
What is the purpose of the urea cycle?
The urea cycle helps to excrete two harmful gases, ammonia and carbon dioxide, from the body. The steps of this cycle take place in the mitochondria and cytoplasm.
Why is it important for urea to be excreted?
Urea serves a second function in the medulla: it is the major source for excretion of nitrogenous waste; large quantities of urea need to be excreted daily. The kidney’s ability to concentrate urea reduces the need to excrete water simply to remove nitrogenous waste.
Do all mammals produce urea?
Nitrogenous wastes in the body tend to form toxic ammonia, which must be excreted. Mammals such as humans excrete urea, while birds, reptiles, and some terrestrial invertebrates produce uric acid as waste.
What is the role of the urea cycle in amino acid metabolism?
The amino acid arginine is synthesized as a product of the urea cycle. The two entering nitrogen atoms exit the cycle as urea, which the liver releases into the blood for disposal, in urine, by the kidneys.
What are the five main reactions involved in urea cycle?
Reactions
| Step | Reactants | Products |
|---|---|---|
| 1 | NH3 + HCO − 3 + 2ATP | carbamoyl phosphate + 2ADP + Pi |
| 2 | carbamoyl phosphate + ornithine | citrulline + Pi |
| 3 | citrulline + aspartate + ATP | argininosuccinate + AMP + PPi |
| 4 | argininosuccinate | arginine + fumarate |
What role does urea have in tubular reabsorption?
The urea reabsorbed increases the medullary concentration of the solute, which is critical for the reabsorption of water from the thin inner medullary part of the descending limb of the loop of Henle. Here, there is no osmotic gradient to cause water movement in the diluting kidney.
What is the function of urea reabsorption in the collecting ducts of the kidney?
In the collecting ducts, urea is reabsorbed together with water. These mechanisms enable the formation of a high-osmolar urea gradient in the renal medulla, which is important for the renal urine concentration.
How is urea produced in mammals?
The urea cycle is the primary mechanism by which mammals convert ammonia to urea. Urea is made in the liver and excreted in urine. The overall chemical reaction by which ammonia is converted to urea is 2 NH3 (ammonia) + CO2 + 3 ATP + H2O → H2N-CO-NH2 (urea) + 2 ADP + 4 Pi + AMP.
Which answer best describes the formation of urea in mammals?
Which answer best describes the formation of urea in mammals? It forms in the kidneys from glycerol and fatty acids.
What is the implication of urea formation during protein metabolism?
Amino acids may also be metabolized through the liver to form urea, which is then excreted in the urine. Body protein stores can be converted back to essential and nonessential amino acids or may be metabolized, forming waste products and ions, which, as previously detailed, are excreted in the urine.