What Happens to Amino Acids When They Are Absorbed?

Amino acids are small biological molecules that serve two purposes in your body: as the building blocks of large proteins and as molecules that par

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Amino acids are small biological molecules that serve two purposes in your body: as the building blocks of large proteins and as molecules that participate in metabolic reactions, such as energy production, within your cells. Protein digestion creates a pool of single amino acids from your dietary protein, which your small intestine then absorbs. The cells throughout your body use these amino acids in a variety of ways.


All amino acids have a similar chemical structure. They contain a central carbon atom, and to this carbon is attached a carboxyl group, consisting of carbon and oxygen, and an amino group made of nitrogen and hydrogen. Amino acids differ, however, in the third group attached to the central carbon. This R-group, or side chain, gives each specific amino acid a different chemical nature, which affects both how it interacts when incorporated into a protein molecule and how your cells metabolize it. Before either of these events can happen, you must first absorb each amino acid.


The absorptive cells, or enterocytes, lining your small intestine create a barrier between your gut and your bloodstream. To reach the cells throughout your body, amino acids must travel from your gut, following digestion, to your blood, and your enterocytes accomplish this with the help of transporter molecules. These transporters are specific for individual amino acids depending on the chemistry of their R-groups. With the help of sodium, the transporter reaches through the cell membrane on the side of the enterocyte adjacent to your gut and grabs a single amino acid. It pulls it inside the enterocyte and releases it, where a different transporter – this one not dependent on sodium – picks it up and carries it to the side of the cell next to your bloodstream. Here it deposits the amino acid into capillaries that enter into your general circulation.

Protein Synthesis

One possible fate of absorbed amino acids is to become incorporated into a new protein. Your cells create new proteins as needed, determined by chemical signals within your cells that direct your genes to specify the order of amino acids required for that particular protein. Individual amino acids join together in a specific sequence, with the amino group of one linking to the carboxyl group of the next. When all necessary amino acids have joined together in this manner, the different R-groups interact to cause the protein to take on a certain conformation. For example, some R-groups may cause the amino acid chain to twist into a spiral or to fold into a sheet, causing the protein to take on a specific shape.


If not needed for protein synthesis, amino acids can take part in metabolism. Your body has the ability to manufacture a subset of amino acids, known as non-essential because you don’t have an absolute requirement for them in your diet. Your cells can make non-essential amino acids by modifying other amino acids or from what’s left over after excess amino acids are broken down. You can also break down amino acids and use their components either as a fuel source for your cells or as a precursor to fatty acids that then store in your adipose tissue.