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Which one of the following enzymes carries on the initial step in the digestion of milk in humans?
A
Trypsin
B
Pepsin
C
Rennin
D
Lipase
Detailed Solution
Milk proteins are first acted upon in the stomach, by the enzymes of gastric juice.
Rennin is the milk-coagulating proteolytic enzyme found in the gastric juice of infants; in calves it is the main milk-digesting enzyme.
In adult humans rennin is absent, and the initial step in the digestion of milk protein (casein) is carried out by pepsin in the acidic medium of the stomach.
Trypsin acts later, in the small intestine, and lipase acts on fats, not on milk protein.
The answer accepted in the key is pepsin.
Note: some books give rennin for this question on the basis of its presence in infants; the key of the source PDF (pepsin) is retained here.
Rennin is the milk-coagulating proteolytic enzyme found in the gastric juice of infants; in calves it is the main milk-digesting enzyme.
In adult humans rennin is absent, and the initial step in the digestion of milk protein (casein) is carried out by pepsin in the acidic medium of the stomach.
Trypsin acts later, in the small intestine, and lipase acts on fats, not on milk protein.
The answer accepted in the key is pepsin.
Note: some books give rennin for this question on the basis of its presence in infants; the key of the source PDF (pepsin) is retained here.