Question

In an abstract written over forty years ago Nelson states that to solve this problem urea is reconverted to amino acids:

"The urea that is formed is hydrolyzed and the nitrogen released is combined with glycerol to form amino acids, which reenter protein synthetic pathways."
Is this correct and, if so, where does the process take place and what are the precise biochemical reactions involved?

Answer 1

The process described in the abstract is slightly misleading; urea is not converted back into amino acids. The urea cycle converts ammonia into urea in the liver, which is then excreted in the urine by the kidneys.

Step-by-step explanation:

The statement in the abstract is not entirely correct as urea itself is not reconverted into amino acids directly. Rather, the urea cycle facilitates the conversion of ammonia to urea for excretion, not the synthesis of amino acids from urea. The urea cycle takes place in the liver and involves five intermediate steps catalyzed by different enzymes. The urea cycle, or ornithine cycle, includes the transformation of ammonia, which is toxic, into urea, a much less toxic compound. This urea is then excreted by the kidneys.

Here's a concise breakdown of the urea cycle process:

1. Ammonia is formed through deamination during amino acid breakdown.
2. Ammonia combines with carbon dioxide in the liver, producing urea via the urea cycle.
3. The process involves key intermediates like L-ornithine and enzymes such as ornithine transcarbamylase.
4. Urea is then transported to the kidneys and excreted in urine.

While amino acids can be catabolized into glucose and ketones, urea does not contribute to these pathways directly but is a downstream byproduct meant to safely remove nitrogen from the body.

Answer 2

The statement is not accurate. Urea is not directly reconverted into amino acids.

Step-by-step explanation:

The process described in the abstract is not correct. Urea, a nitrogenous waste product, is typically produced in the liver through the breakdown of amino acids and other nitrogen-containing compounds.

However, urea is not directly reconverted into amino acids. Instead, urea is excreted from the body through the urine, primarily as a means to eliminate excess nitrogen.

The actual process of nitrogen metabolism involves the urea cycle, which takes place in the liver. In this cycle, ammonia, a toxic byproduct of protein metabolism, is converted into urea.

Urea is then transported to the kidneys and excreted in urine. The cycle is essential for maintaining nitrogen balance in the body.

The biochemical reactions involved in the urea cycle include the combination of ammonia with carbon dioxide to form carbamoyl phosphate, followed by a series of reactions that ultimately produce urea.

This cycle is crucial for detoxifying ammonia and preventing its accumulation in the bloodstream.

In summary, the abstract's statement is incorrect, as urea is not reconverted into amino acids.

Instead, urea is a product of the urea cycle, a biochemical process that occurs in the liver to eliminate excess nitrogen.