Question

Most amino acids are absorbed by in intestine.

• A. active transport
• B. simple diffusion
• C. osmosis
• D. $\mathrm{facilitated}\mathrm{diffusion}$

Answer 1

The correct option is D $\mathrm{facilitated}\mathrm{diffusion}$

The mechanism by which amino acids are absorbed is identical to that of monosaccharides. The lumenal plasma membrane of the absorptive cell bears three amino acid-sodium dependent transporters:

• For acidic amino acids
• For basic amino acids
• For neutral amino acids

These transporters bind amino acids only after binding to sodium. The fully loaded transporter then undergoes a conformational change that dumps sodium and the amino acid along with it, into the cytoplasm, followed by its reorientation to its original form. Some amino acids require active transport across the membrane while others, only facilitated transport.