Urea vs Uric Acid
Human body produces a lot of unnecessary and toxic products in the metabolism. These substances should be converted to less toxic substances till they are removed from the body. Excretory system is important for the removal for these substances. Our main excretory organ is kidney. Urine is produced in the kidneys, and this is the primary method of excreting the excess and unnecessary substances from our bodies. Except the kidneys, our skin also acts as an excretory organ. Through sweat, some things are excreted. Ammonia, urea and uric acid are nitrogenous excretory products which are removed from the body like this. Depending on the water availability and habitat of the organisms, the type of excretory product they produce differs. Ammonia is highly toxic, and it is produced as a by-product in the protein metabolism. This is the excretory product of fresh water fish. Since they can easily remove ammonia into water, they can dilute its toxicity but, in humans, the water availability is somewhat lower than fish, and until it is removed from the body it has to be stored inside. So a toxic excretory product like ammonia is converted to less toxic urea.
Urea has the molecular formula of CO(NH2)2 and the following structure.
It is a carbamide with the functional group C=O. Two NH2 groups are bonded to the carbonyl carbon from two sides. Urea is naturally produced in mammals in nitrogen metabolism. This is known as the urea cycle, and oxidation of ammonia or amino acids produce urea inside our bodies. Most of urea is excreted through kidneys with urine, whereas some are excreted with sweat. The high water solubility of urea is helpful when excreting it from the body. Urea is a colorless, odorless solid, and it is non toxic. Other than being a metabolic product, its main use is to produce fertilizer. Urea is one of the most common nitrogen releasing fertilizers, and it has a high nitrogen content compared to other solid nitrogenous fertilizers. In soil, urea is converted to ammonia and carbon dioxide. This ammonia can be converted to nitrite by soil bacteria. Further, urea is used to produce explosives like urea nitrate, and as a raw material to produce chemicals like plastics and adhesives.
Uric acid is a cyclic compound containing nitrogen. Its formula is C5H4N4O3 and has the following structure.
The water solubility of uric acid is generally low. This is produced in the purine (a nucleotide) metabolism. In humans, the produced uric acid is excreted with urine. This is the main excretory product of reptiles and birds. In them, uric acid is excreted with feces as a dry mass, so the water loss is very low. Uric acid is a diprotic acid. Therefore, at high pH values it forms a urate ion.
What is the difference between Urea and Uric Acid?
• Uric acid is a bicyclic molecule and urea is not so.
• Producing uric acid needs a high energetic metabolic pathway compared to urea production.
• Water loss, when excreting uric acid, is lower than the water loss with urea.
• Uric acid is the main nitrogenous excretory product of reptiles and birds whereas urea is the main excretory product of humans.
• Uric acid is excreted as a solid with fecal matter in birds and reptiles where urea in humans is excreted with urine as a liquid.