The process of protein turnover includes:
a. excreting old amino acids that are left from cell breakdown.
b. synthesizing intestinal cells, which live for 3 to 4 months.
c. eating food sources of amino acids every day to grow new cells and replace worn-out ones.
d. preserving all old amino acids in the body to be re-circulated.
e. circulating proteins in the bloodstream to replenish peptide chains.

c. eating food sources of amino acids every day to grow new cells and replace worn-out ones.

Explanation:

Proteins are one of the macromolecules present in cells to serve both structural and functional roles. Cells continuously form new proteins to replace the worn-out ones. Proteins are polymers of amino acids. Many amino acids are synthesized in cells while the food we eat serves as a source of essential amino acids that cannot be formed in the body.

Digestion of proteins present in the food item releases the amino acids that become part of the amino acid pool of the cell. These amino acids serve as a monomer for protein synthesis. This process of protein synthesis and protein breakdown is called protein turn over.