Digestion of proteins begins in the where and mix with food to break down protein into .
a. stomach; amylase; HCl; amino acids
b. mouth; pepsin; HCl; fatty acids
c. stomach; lipase; HCl; amino acids
d. stomach; pepsin; HCl; amino acids
The Correct Answer and Explanation is:
The correct answer is:
d. stomach; pepsin; HCl; amino acids
Explanation
Protein digestion in humans begins in the stomach, a key organ in the gastrointestinal tract responsible for breaking down food into smaller, absorbable components. The process is primarily driven by the action of hydrochloric acid (HCl) and the enzyme pepsin.
When food enters the stomach, specialized cells in the stomach lining secrete HCl, which serves multiple purposes. First, it creates a highly acidic environment (pH 1.5–3.5), which denatures proteins — this means it unfolds the complex structures of proteins, making them more accessible to enzymatic attack. HCl also converts the inactive form of pepsin, known as pepsinogen, into its active form, pepsin.
Pepsin is a protease enzyme that breaks the peptide bonds between amino acids in proteins, resulting in smaller chains known as peptides. Though the process in the stomach doesn’t completely break proteins down into individual amino acids, it marks the beginning of protein digestion. Complete digestion into amino acids continues later in the small intestine with the help of other enzymes like trypsin and chymotrypsin.
The mouth plays no significant role in protein digestion, as it primarily focuses on carbohydrate digestion through amylase. Lipase, mentioned in one of the incorrect options, is involved in fat digestion, not protein digestion.
Therefore, the most accurate and comprehensive choice is:
“stomach; pepsin; HCl; amino acids” — even though the final product of digestion isn’t fully amino acids until later stages, this choice best represents the initial breakdown process of proteins in the digestive system.
In summary, protein digestion starts in the stomach, where HCl and pepsin work together to initiate the breakdown of proteins into smaller peptide chains, ultimately leading to the production of amino acids further down the digestive tract.
