Final answer:
Only individual amino acids, not intact proteins, are absorbed into the blood after digestion. The transport of amino acids is facilitated by hormones and can be affected by pH changes. Small changes in amino acid sequences can have major effects on protein function, as seen in disorders like sickle cell anemia.
Step-by-step explanation:
Only separate amino acids enter the blood, which is a true statement. During digestion, proteins in food are broken down into amino acids or small peptides such as dipeptides and tripeptides. These are then actively transported into the absorptive epithelial cells of the intestine. Within these cells, peptides are further broken down into amino acids before they are released into the capillary blood via diffusion.
The transport of amino acids into the blood capillaries of the mucosa is essential for them to be carried in the plasma to the liver and other tissues. Hormones like insulin and glucagon play a role in mediating the reabsorption and transportation of amino acids, minimizing their loss in urine and facilitating their physiological use. If the pH outside the cell decreases, the transport of amino acids into the cell typically decreases due to altered transporter activity in most cases.
Furthermore, not all amino acid changes lead to functional deficiencies in proteins. For instance, the substitution of a single amino acid in hemoglobin can result in sickle cell anemia, showcasing the critical role that the correct amino acid sequence plays in protein function.