Digestive Enzymes

Question 1

Carbohydrate Digestive Enzymes:
Mouth (2 in oral cavity)
Small Intestine (1 in lumen, 6 on brush border)

Answer 1

Mouth: salivary alpha-amylase and lysozyme
Small Intestine: pancreatic alpha-amylase (lumen) and glucoamylase, dexrinase, sucrase-isomaltase, maltase, lactase-cerebrosidase, trehalase (brush border)

Question 2

Salivary alpha-Amylase:
Area of Operation
Specific Cleavage Function (Factors and Products)
Limitations

Answer 2

Mouth
Cleaves alpha(1-4) glycosidic bonds of starch to glucose, maltose, maltotriose and alpha-limit dextran
Limited by pH - operates in saliva, digested in stomach

Question 3

Lysozyme:
Area of Operation
Specific Cleavage Function (Factors and Products)
Main Physiological Function

Answer 3

Mouth
Cleaves beta(1-4) glycosidic bonds in peptidoglycans
Kill bacteria in mouth

Question 4

Pancreatic alpha-Amylase:
Areas of Production and Operation
Specific Cleavage Function
Factors and Products

Answer 4

Produced in pancreas and secreted into small intestine
Cleaves alpha(1-4) glycosidic bonds of starch to glucose, maltose, maltotriose and alpha-limit dextran

Question 5

Glucoamylase:
Area of Operation
Specific Cleavage Function
Factors and/or Products

Answer 5

Small intestine brush border
Exoglycosidase of alpha(1-4) bonds at nonreducing end of starches
Products - maltose and maltotriose

Question 6

Dextrinase:
Area of Operation
Specific Cleavage Function
Factors and/or Products

Answer 6

Small intestine brush border
Cleaves dextrins (low molecular weight oligosaccharides) produced by earlier hydrolysis
Factor - alpha-limit dextran

Question 7

Sucrase-Isomaltase:
Area of Operation
Specific Cleavage Function
Factors and/or Products

Answer 7

Small intestine brush border
Sucrase: cleaves sucrose into fructose and glucose, maltose into 2 glucose molecules, and maltotriose into 3 glucose molecules
Isomaltase: cleaves alpha(1-6) bonds in isomaltose and alpha-limit dextran

Question 8

Maltase:
Area of Operation
Factors and Products

Answer 8

Small intestine brush border

Cleaves maltose into 2 glucose molecules

Question 9

Lactase-Cerebrosidase:
Area of Operation
Factors and/or Products

Answer 9

Small intestine brush border
Lactase: cleaves lactose into glucose and galactose, and cellobiose into 2 glucose molecules
Cerebrosidase: cleaves glucocerebroside and galactocerebroside (glycosphingolipids)

Question 10

Trehalase:
Area of Operation
Factors and/or Products
Where it is Found

Answer 10

Small intestine brush border
Cleaves trehalose into 2 glucose molecules
Common in mushrooms and insects

Question 11

Protein Digestive Factors and Enzymes:
Stomach (1 factor, 1 enzyme)
Small Intestine (7)

Answer 11

Stomach: gastric acid, pepsin

Small intestine: trypsin, chymotrypsin, elastase, carboxypeptidases A and B, aminopeptidases, dipeptidases

Question 12

Significance of gastric acid for proteins.

Answer 12

Facilitates denaturing of dietary protein

Makes peptide bonds more accessible for proteases

Question 13

Pepsin:
Production and Activation
Area of Operation
Specific Cleavage Function
Factors and/or Products
Inactivation

Answer 13

Produced and secreted as pepsinogen by gastric chief cells and stimulated by gastric acid for autocleavage from N-terminus
Stomach (operational at pH 1.5 - 2.0)
Endopeptidase - cleaves nonterminal and terminal peptide bonds on amino side of hydrophobic AAs
Carboxyl protease - Asp protease (catalyzed by Asp)
Produces peptone (mixture of oligopeptides and free AAs)
Inactivated by high pH in duodenum

Question 14

Trypsin:
Production and Activation
Area of Operation
Specific Cleavage Function
Factors and/or Products

Answer 14

Produced and secreted as trypsinogen by pancreas and activated by trypsin or enteropeptidase
Endopeptidase - cleaves peptide bonds on carboxyl side of Lys and Arg except when followed by Pro
Ser protease

Question 15

Chymotrypsin:
Production and Activation
Area of Operation
Specific Cleavage Function
Factors and/or Products

Answer 15

Produced and secreted as chymotrypsinogen by pancreas and activated in intestinal lumen by trypsin (active forms - pi-chymotrypsin and alpha-chymotrypsin)
Endopeptidase - cleace peptide bonds on carboxyl side of hydrophobic AAs

Question 16

Elastase:
Production and Activation
Area of Operation
Specific Cleavage Function
Factors and/or Products

Answer 16

Produce and secreted as proelastase by pancreas and activated in intestinal lumen by trypsin
Endopeptidase - cleaves peptide bonds on carboxyl side of small amino acids (ex. Gly)
Ser protease

Question 17

Carboxypeptidases A and B:
Production and Activation
Area of Operation
Specific Cleavage Function
Factors and/or Products

Answer 17

Produce and secreted as procarboxypeptidases by pancreas and activated in intestinal lumen by trypsin
Exopeptidases
A: cleaves of hydrophobic AAs
B: cleaves off basic AAs
Zn2+ metalloprotease

Question 18

Aminopeptidase:
Area of Operation
Specific Cleavage Function

Answer 18

Small intestine brush border

Exopeptidase - cleaves off one AA from N-terminus

Question 19

Dipeptidase:
Area of Operation
Specific Cleavage Function

Answer 19

Small intestine brush border

Cleaves dipeptides into AAs

Question 20

Lipid Digestive Enzymes:
Preparation (1 mouth, 1 stomach)
Small Intestine (1 factor, 2 enzymes)
Define “Emulsification”

Answer 20

Mouth: lingual lipase
Stomach: gastric lipase
Small intestine: bile salts (factor), pancreatic lipase, colipase
Emulsification - creation of a mixture of a two-phase solution (ex. fat and water)

Question 21

Bile Salts:
Production, Storage and Secretion
Purpose (2)

Answer 21

Produced and secreted in bile by hepatocytes
Stored in gallbladder
Secreted into small intestine
Leads to greater emulsification (mixed micelle formation)
Necessary for absorption of other dietary lipids (ex. cholesterol and fat-soluble vitamins)

Question 22

Lingual Lipase:
Specific Cleavage
Products

Answer 22

Cleaves small percentage of dietary fat

Produces monoglycerides, diglycerides and free fatty acids

Question 23

Gastric Lipase:
Description
Specific Cleavage
Products

Answer 23

Acid-tolerant emulsification enzyme that digests 10 to 20% of dietary fat
Cleaves triglycerides
Produces monoglycerides, diglycerides and free fatty acids

Question 24

Pancreatic Lipase:
Production and Secretion
Specific Cleavage
Products

Answer 24

Produced by pancreas and secreted into small intestine
Binds to fat emulsion droplets and cleaves triglycerides
Produces 2 free fatty acid anions and a 2-monoacylglycerol molecule

Question 25

Colipase:
Production, Secretion and Activation
Purpose

Answer 25

Produced by pancreas as procolipase and secreted into small intestine to be activated by trypsin
Maintains activity of pancreatic lipase in presence of bile salts

Question 26

Nucleic Acid Digestive Enzymes:
Small Intestine Lumen (4)
Small Intestine Brush Border (2)

Answer 26

Lumen: DNAases, RNAases, exonucleases, endonucleases

Bursh border: nucleosidases and phosphatases

Question 27

DNAases, RNAases, Exonucleases and Endonucleases:
Function
DNAase Products (given DNA strand)
RNAase Products (given RNA strand)

Answer 27

Break down nucleic acids into monomeric nucleotides
DNAase: dATP, dGTP, TTP, dCTP (notice TTP)
RNAase: ATP, GTP, UTP, CTP

Question 28

Nucleosidases:
Specific Cleavage
Products

Answer 28

Cleave ribose or deoxyribose and nitrogenous bases

Adenine, guanine, cytosine, thymine, uracine)

Question 29

Phosphatases:
Specific Cleavage
Products

Answer 29

Cleave phosphate groups and nucleotides

Adenosine, deoxyadenosine, cytidine, deoxycytidine, thymidine, guanosine, deoxyguanosine, uridine

Question 30

Microbial-Based Digestion in Humans:
Define “Dietary Fiber” and Give Examples (6)
Products of Bacterial Digestion (7)

Answer 30

Dietary fiber - plant polymers resistant to human digestive enzymes that help move food along GI tract by providing bulk (ex. cellulose, hemicellulose, inulin, pectin, lignin, suberin)
Products - hydrogen gas, methane, carbon dioxide, acetate, propionate, butyrate, lactate