Proteins are turned into which acids by our digestive system?

Question

Accepted Answer

The correct option is (3):
Proteins are complex, large-chain biological molecules known as polymers. Their fundamental building blocks, or monomers, are **Amino acids**. The purpose of the digestive system, through a process called hydrolysis, is to systematically break down these large protein chains (polypeptides) into their smallest, absorbable units. This breakdown is facilitated by specific enzymes, such as pepsin in the stomach and trypsin and peptidases in the small intestine. The end product of complete protein digestion is the release of individual amino acids, which are then absorbed across the intestinal wall into the bloodstream to be used by the body for growth, repair, and synthesis of new proteins.

The incorrect option is (1):
Ascorbic acid is the chemical name for Vitamin C, which is an essential water-soluble micronutrient. It is obtained through the diet (from fruits and vegetables) and is absorbed directly into the body; it is not the product of breaking down larger macromolecules like proteins. Its primary roles include acting as an antioxidant and serving as a co-factor in collagen synthesis, completely unrelated to the digestive end-product of proteins.

The incorrect option is (2):
Hydrochloric acid (HCl) is a strong acid secreted by the parietal cells in the stomach. Its function is to create the highly acidic environment necessary to denature (unfold) proteins and activate the protein-digesting enzyme pepsin, thus *initiating* protein digestion. HCl is an active agent or catalyst of the digestive process, not the final product that results from the breakdown of the protein itself.

The incorrect option is (4):
Lactic acid is a byproduct of anaerobic metabolism, which occurs when muscle cells produce energy (ATP) without sufficient oxygen, such as during intense, short-duration exercise. It is a metabolic substance related to muscle function and fatigue. It is not involved in the chemical breakdown of dietary proteins within the stomach or small intestine.