Final answer:
The uptake of amino acids into intestinal cells is described as active transport, where cellular energy is used to move amino acids against their concentration gradient.
Step-by-step explanation:
The mechanism of uptake of amino acids into intestinal cells is termed active transport. Active transport mechanisms are responsible for absorbing most proteins as amino acids, the breakdown products of proteins, primarily in the duodenum and jejunum of the small intestine. Proteins within the cell membrane act as "pumps," utilizing cellular energy (ATP) to move amino acids from an area of lower concentration to one of higher concentration. This is necessary because amino acids are polar molecules and cannot easily pass through the hydrophobic lipid bilayer of the cell membrane. Notably, the transport of amino acids is typically linked to the active transport of sodium.