Biochemistry of the GI tract

Question 1

what enzyme begins breakdown of starch? what is its chemical action?

Answer 1

salivary a-amylase

hydrolyzes a1,4-glycosidic bonds

Question 2

what does the pancreas secrete to neutralize chyme?

Answer 2

NaHCO3

Question 3

what is the chemical action of pancreatic a-amylase?

Answer 3

hydrolyzes a1,4-glycosidic bonds

Question 4

what enzymes complete the breakdown of sugars into mono, di, and trisaccharides?

Answer 4

isomaltase and a-glucosidase

Question 5

what is the role of maltase?

Answer 5

generates two glucoses from maltose

Question 6

what is the role of lactase?

Answer 6

generates glucose and galactose from lactose

Question 7

what is the role of sucrase / isomaltase?

Answer 7

generates glucose and fructose from sucrose

Question 8

which enzyme is responsible for bringing glucose from the lumen into the intestinal epithelium? what is required for this transport?

Answer 8

SGLT1

sodium

Question 9

which enzyme is responsible for bringing fructose from the lumen into the intestinal epithelium?

Answer 9

GLUT5

Question 10

which enzyme is responsible for bringing glucose from the intestinal epithelium into circulation?

Answer 10

GLUT2

Question 11

which enzyme is responsible for bringing fructose from the intestinal epithelium into circulation?

Answer 11

GLUT2

Question 12

what explains the diarrhea seen in lactose intolerance?

Answer 12

2 and 3 carbon metabolites draw water into the intestine

Question 13

which gastric enzyme breaks down proteins?

Answer 13

pepsin

Question 14

which pancreatic enzymes break down proteins?

Answer 14

trypsin, chymotrypsin, elastase, carboxypeptidase

Question 15

what are the brush border enzymes that break down proteins?

Answer 15

endopeptidase, aminopeptidase, dipeptidase

Question 16

which enzyme has a pivotal role in zymogen activation?

Answer 16

enteropeptidase

Question 17

what is the role of enteropeptidase?

Answer 17

catalyzes trypsinogen to trypsin

Question 18

what is the role of trypsin?

Answer 18

conversion of

chymotrypsinogen - chymotrypsin
proelastase - elastase
procarboxypeptidase - carboxypeptidase

Question 19

what is the role of trypsin inhibitor?

Answer 19

prevents premature activation of trypsin in the pancreas

Question 20

what is the mechanism of pancreatic autodigestion?

Answer 20

blockage of pancreatic duct or deficiency of trypsin inhibitor

Question 21

how does CF affect the GI system?

Answer 21

CFTR deficiency causes thickening of pancreatic mucus

secretion of pancreatic enzymes is impaired in 80% of CF patients

Question 22

amino acid uptake is accomplished by what family of proteins?

Answer 22

amino acid transporters (SLCs)

Question 23

what is detected on the breath in lactose intolerance breath testing?

Answer 23

hydrogen

Question 24

what is the cause of cystinuria? what is the result?

Answer 24

inefficient re-uptake of cystin (cys-cys) in kidney

cystin crystals form in GU tract

Question 25

what is the cause of hartnup disease? what is the result?

Answer 25

defective uptake in neutral amino acids from intestine and kidney filtrate

shortage of tryptophan for NAD synthesis causes pellagra like symptoms

Question 26

what is responsible for solubilizing large lipid droplets?

Answer 26

bile salts

Question 27

what is the role of pancreatic lipase?

Answer 27

separates two fatty acids from TAG

Question 28

which enzyme is responsible for separating two fatty acids from TAG?

Answer 28

pancreatic lipase

Question 29

enterocytes package lipids into what molecule?

Answer 29

Apo48-containing chylomicrons