Q.Describe the process of digestion of protein in stomach.

Protein digestion begins in the stomach. The gastric glands of the stomach wall secrete gastric juice, made up of:

• Hydrochloric acid (HCl), from the oxyntic (parietal) cells — it produces the strongly acidic environment of the stomach (around pH 1.8), kills ingested microorganisms, and, most importantly for protein digestion, converts the inactive pepsinogen into active pepsin.
• Pepsinogen, from the chief (peptic) cells — the inactive precursor of the main gastric protease. Once activated to pepsin by HCl, it can also activate further pepsinogen molecules (autocatalysis).
• Mucus, which protects the stomach lining from the acid and from pepsin itself.
• Rennin (mainly in infants) — coagulates/curdles the milk protein casein into paracasein, which is then acted upon by pepsin; this is important for digesting milk in early life. …

Identify the gastric secretions involved (HCl, pepsinogen, mucus, rennin), state how pepsinogen is activated (by HCl, then autocatalytically), and describe what pepsin actually does to …

• Stating that proteins are broken all the way down to amino acids in the stomach — pepsin only produces proteoses/peptones; full breakdown happens later in the small intestine. …