9.3 Digestive Enzymes

Question 1

What are digestive enzymes?

Answer 1

proteins that speed up specific chemical reactions

Question 2

What is starch?

Answer 2

a carbohydrate that’s digestion begins in the mouth

Question 3

What is salivary amylase?

Answer 3

an enzyme in saliva that digests starch to maltose

Question 4

What is maltose?

Answer 4

disaccharide molecule that cannot be absorbed by the intestine

Question 5

What is glucose?

Answer 5

a monosaccharide that can be absorbed, digestive action in the small intestine converts maltose to glucose

Question 6

Where does protein digestion begin?

Answer 6

in the stomach

Question 7

Why are gastric juices secreted by gastric glands very acidic?

Answer 7

(pH 2) because it contains hydrochloric acid

Question 8

What is pepsinogen?

Answer 8

a precursor that is converted to the enzyme pepsin when exposed to HCl that is present in gastric juice

Question 9

What is pepsin?

Answer 9

an enzyme that acts on proteins (polymers of amino acids) to produce peptides

Question 10

Describe peptides from the stomach.

Answer 10

usually too large to be absorbed by the intestinal lining, but later in the small intestine they are broken down to amino acids

Question 11

What is pancreatic juice?

Answer 11

enters the duodenum and has a basic pH because it contains NaHCO3 (sodium bicarbonate)

Question 12

What does NaHCO3 do?

Answer 12

neutralizes the acid in chyme, producing the slightly basic pH that is optimum for pancreatic enzymes including pancreatic amylase and trypsin

Question 13

What is pancreatic amylase?

Answer 13

a pancreatic enzyme that digests starch

Question 14

What is trypsin?

Answer 14

a pancreatic enzyme that digests protein

Question 15

What is trypsin secreted as?

Answer 15

trypsinogen, which is converted to trypsin in the duodenum

Question 16

What is lipase?

Answer 16

a pancreatic enzyme that digests fat molecules in the fat droplets after they have been emulsified by bile salts

Question 17

What are fats?

Answer 17

triglycerides, composed of glycerol and three fatty acids

Question 18

What are the end products of lipase digestion?

Answer 18

glycerol and fatty acid molecules that are small enough to cross the cells of the intestinal villi where absoprtion takes place

glycerol and fatty acids enter the cells of the villi, and within these cells, they are rejoined and packaged as lipoprotein droplets before entering the lacteals

Question 19

What is peptidases?

Answer 19

enzyme secreted by the surface cells of the small intestine villi and completes the digestion of proteins to amino acids

Question 20

What is maltase?

Answer 20

enzyme secreted by the surface cells of the small intestine villi and completes the digestion of starch to glucose

Question 21

What is lactose intolerance caused by?

Answer 21

fermentation of of non-digested lactose by intestinal bacteria

Question 22

When do enzymes function best?

Answer 22

at an optimum temperature and pH, which helps maintain the proper shape to fit their substrate

Question 23

What does the compartmentalization of the digestive system do?

Answer 23

assists in the regulation of enzymatic activity

Question 24

Why is enzymatic activity largely controlled by pH?

Answer 24

because the entire digestive system of humans is maintained at a constant temperature of 37 C

Question 25

What is the pH of the stomach?

Answer 25

between 1 and 2, allowing the activation of pepsinogen enzyme

Question 26

When does the pH of the stomach change?

Answer 26

shortly after chyme proceeds into the duodenum, the sodium bicarbonate released from the pancreas returns the pH to around 7.4-7.8

Question 27

What does the change in pH of the stomach do?

Answer 27

serves the activate digestive enzymes released by the pancreas, thus allowing the digestion of carbohydrates, fats, and proteins