Library · Physiology
Protein metabolism
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A protein is a chain of amino acids, or several chains together. When the body needs to take one apart, it uses enzymes called proteases, which cut the chain into shorter pieces and finally into free amino acids.
Of all the amino acids that exist, there are nine the human body simply cannot make. Those are called essential, and they can only come from outside the body, in food or in a supplement. It is like a wall the body builds, except for nine kinds of brick it cannot make.
There is a way to tell which way the balance tips: compare how much nitrogen goes into the body with how much is excreted. That is called nitrogen balance. If more comes in than goes out, the balance is positive, which means protein is being built up overall.
And when an amino acid is broken down it does not vanish: it is deaminated, that is, it loses its amino group, and ends up as a metabolic intermediate such as acetyl-CoA or pyruvate.
In brief
A protein is one or more chains of amino acids, and proteases break it into peptides and free amino acids.
Nine amino acids are essential because the body cannot make them and they must come from food or supplements.
A brick wall the body builds, except for nine kinds of brick it cannot make.
Nitrogen balance compares what goes in with what comes out; positive means net protein synthesis.
As they break down, amino acids are deaminated and converted into metabolic intermediates, such as acetyl-CoA or pyruvate.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingBiochemistry, Amino Acid Synthesis and Degradation, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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