Describe the process of digestion of protein in the stomach.

(N/A) The digestion of proteins begins in the stomach and is completed in the small intestine.
The digestive juice secreted by the gastric glands present in the stomach wall is called gastric juice. The food that enters the stomach becomes acidic upon mixing with this gastric juice.
The main components of gastric juice are hydrochloric acid $(HCl)$, pepsinogen, mucus, and rennin (in infants). Hydrochloric acid creates an acidic medium $(pH \approx 1.8)$ so that the inactive enzyme pepsinogen is converted into its active form, pepsin.
$Pepsinogen \xrightarrow{HCl} Pepsin$
Pepsin is a proteolytic enzyme that converts proteins into proteoses and peptones.
$Proteins \xrightarrow{Pepsin} Proteoses + Peptones$
Rennin is a proteolytic enzyme found in gastric juice of infants, which helps in the digestion of milk proteins. It is released in an inactive form called prorennin, which is activated by $HCl$.
$Prorennin \xrightarrow{HCl} Rennin$
$Casein (milk protein) \xrightarrow{Rennin} Paracasein \to Calcium \ Paracaseinate$