Energy value of proteins 1 g of proteins provides 4 kcal of energy (17 kJ).
Digestion of proteins
During digestion, water and enzymes break protein chains into separate amino acids. This process is called hydrolysis. Mouth: food is chewed into small pieces by the teeth. Stomach: secretes gastric juice containing: • hydrochloric acid (HCL), which denatures proteins
• the enzyme rennin, which breaks down caseinogen into casein
• the enzyme pepsin, which breaks down proteins into peptones.
Pancreas: secretes pancreatic juice into the duodenum (the first part of the small intestine). The juice contains the enzyme trypsin that breaks down peptones into peptides.
Small intestine: the ileum (final section of the small intestine) secretes intestinal juice containing the enzyme peptidase that breaks down peptides into amino acids.
The amino acids are now ready to be absorbed and utilised by the body.
Gastric juice Rennin Pepsin
Pancreatic juice Trypsin Liver
Duodenum Pancreas
Large intestine Ileum
Anus Digestive system
Organ or gland Secretion Enzymes Substrate Product Stomach
Caseinogen Proteins
Pancreas
Small intestine (ileum)
Peptones Intestinal juice Peptidase Peptides
Casein Peptones
Peptides
Amino acids
? Complete the following statement in relation to the digestion of protein using the words listed below.
enzyme pancreas casein
In the stomach the _______________ rennin changes caseinogen to ______________.
In the duodenum the enzyme trypsin from the _______________ changes peptones to peptides. (6) OL
Leaving Certificate Home Economics 15
A product is the outcome of a reaction between an enzyme and a substrate.
L i
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A substrate is the substance on which an enzyme acts.
