How are proteins absorbed in the small intestine?

Proteins are absorbed in the small intestine through the process of enzymatic breakdown and active transport.

In the small intestine, proteins undergo a complex process of digestion and absorption. Initially, proteins are broken down into smaller units, known as peptides, by enzymes such as pepsin in the stomach and trypsin and chymotrypsin in the small intestine. These enzymes cleave the protein molecules at specific points, resulting in smaller peptide chains.

The next step in the process involves the action of peptidases, which are enzymes that break down these peptides into individual amino acids. This process is known as hydrolysis. Peptidases are located on the brush border (the microvilli) of the small intestine cells, which increases the surface area for absorption.

Once the proteins have been broken down into amino acids, they are ready to be absorbed. This is achieved through a process known as active transport. Active transport requires energy as it involves the movement of substances against a concentration gradient, from an area of lower concentration to an area of higher concentration. In the case of amino acids, they are transported across the cell membrane of the small intestine cells into the bloodstream.

Specific transport proteins in the cell membrane recognise and bind to the amino acids, facilitating their transport into the cell. Once inside the cell, these amino acids can be used for various functions, such as the synthesis of new proteins, energy production, or other metabolic processes.

In summary, the absorption of proteins in the small intestine involves a series of enzymatic reactions that break down proteins into amino acids, followed by active transport of these amino acids into the cells of the small intestine and then into the bloodstream.