The digestion of proteins begins in the stomach and is completed in the small intestine. The enzymes that act on proteins are known as proteases.Digestion in\xa0the stomach: The digestive juice\xa0secreted in the gastric glands present on the stomach walls is called gastric juice. The main components of gastric juice are HCl, pepsinogen, and rennin. The food that enters the stomach becomes acidic on mixing with this gastric juice.The acidic medium converts inactive pepsinogen into active pepsin. The active pepsin then converts proteins into proteases and peptides.Proteins {tex}\\begin{array}{l}\\xrightarrow{Pep\\sin}\\\\\\end{array}{/tex} Proteoses + PeptidesThe enzyme rennin\xa0plays an important role in the coagulation of milk.Digestion in\xa0the small intestine: The food from the stomach is acted upon by three juices present in the small intestine – pancreatic juice and intestinal juice (known as succus entericus).Action of pancreatic juicePancreatic juice contains a variety of inactive enzymes such as trypsinogen, chymotrypsinogen, and carboxypeptidases. The enzymes are present in an inactivated state. The enzyme enterokinase secreted by the intestinal mucosa activates trypsinogen into trypsin.Trypsinogen{tex}\\begin{array}{l}\\xrightarrow{\\;Enterokinase}\\\\\\end{array}{/tex}Trypsin + Inactive peptideThe\xa0activated trypsin then activates the other enzymes of pancreatic juice.Chymotrypsinogen\xa0is a proteolytic enzyme that breaks down proteins into peptides.Chymotrypsinogen\xa0{tex}\\begin{array}{l}\\xrightarrow{Tryp\\sin}\\\\\\end{array}{/tex}\xa0ChymotrypsinProteins{tex}\\begin{array}{l}\\xrightarrow{Chymotryp\\sin}\\\\\\end{array}{/tex}\xa0PeptidesCarboxypeptidases act on the carboxyl end of the peptide chain and help in releasing the last amino acids.Peptides{tex}\\begin{array}{l}\\xrightarrow{\\;Carboxypeptidase}\\\\\\end{array}{/tex}Smaller peptide chain + Amino acidsAction of bile juiceBile juice has bile salts such as bilirubin and biliverdin which break down large, fat globules into smaller globules so that pancreatic enzymes can easily act on them. This process is known as emulsification of fats. Bile juice also makes the medium alkaline and activates lipase. Lipase then breaks down fats into diglycerides and monoglycerides.Action of intestinal juiceIntestinal juice\xa0contains a variety of enzymes. Pancreatic amylase digests polysaccharides into disaccharides. Disaccharidases such as maltase, lactase, sucrase, etc., further digest the disaccharides.The\xa0proteases hydrolyse peptides into dipeptides and finally into amino acids.\xa0{tex}\\begin{array}{l}\\xrightarrow{dipeptides}\\\\\\end{array}{/tex} Amino acidsPancreatic lipase breaks down fats into diglycerides and monoglycerides.The nucleases break down nucleic acids into nucleotides and nucleosides.\xa0