Anatomy & Physiology: Digestive Enzymes

Digestive Enzymes

During digestion, four different groups of molecules are commonly encountered. Each is broken down into its molecular components by specific enzymes:

Complex carbohydrates, or polysaccharides (such as starches), are broken down into oligosaccharides (consisting of two to ten linked monosaccharides), disaccharides (such as maltose), or individual monosaccharides (such as glucose or fructose). Enzymes called amylases break down starch.
Proteins are broken down into short chains of amino acids (peptides) or individual amino acids by enzymes called proteases.
Lipids are broken down into glycerol and fatty acids by enzymes called lipases.
Nucleic acids are broken down into nucleotides by enzymes called nucleases.

A summary of enzymes and their substrates (substances upon which enzymes operate) appears in Table 1.

Table 1. Enzymes and Their Substrates
Enzyme	Substrate	Products of Enzyme Activity
Saliva
salivary amylase	starches	maltose, oligosaccharides
Gastric enzyme (chief cells of stomach)
pepsin	proteins	peptides
Pancreatic enzymes (acinar cells of pancreas)
pancreatic amylase	starches	maltose, oligosaccharides
trypsin	proteins	peptides
chymotrypsin	proteins	peptides
carboxypeptidase	proteins	peptides, amino acids
pancreatic lipase	fats	fatty acids, monoglycerides
nucleases	RNA, DNA	nucleotides
Small intestine (brush border cells on the villi of the small intestine)
dextrinase	oligosaccharides	glucose
maltase	maltose	glucose
sucrase	sucrose	glucose, fructose
lactase	lactose	glucose, galactose
aminopeptidase	peptides	peptides, amino acids
dipeptidase	dipeptides	amino acids
nucleosidases	nucleotides	nitrogen bases, ribose, deoxyribose, phosphates
phosphatases	nucleotides	nitrogen bases, ribose, deoxyribose, phosphates

Digestive Enzymes