Biochem of the GI tract

Question 1

What is the enzyme in the mouth that aids in digesting starch? Lipids?

Answer 1

alpha amylase

Lingual lipase

Question 2

What is the zymogen secreted by the stomach that aids in food digestion and turning on other enzymes?

Answer 2

Pepsinogen

Question 3

What activates pepsinogen?

Answer 3

low pH

Question 4

What cells in the stomach secrete pepsinogen?

Answer 4

Chief cells

Question 5

What is the enzyme secreted by the pancreas that is secreted in its active form?

Answer 5

Pancreatic alpha amylase

Question 6

What are the two mineral chemical secreted by the pancrase?

Answer 6

NaCl

NaHCO3

Question 7

The liver synthesizes bile acids from what?

Answer 7

Cholesterol

Question 8

Where are the enzymes that convert carbs and proteins into absorbable low molecular weight molecules?

Answer 8

Brush border of the intestines

Question 9

What form must carbs be in to be absorbed into the intestines?

Answer 9

Monosaccharides

Question 10

What are the two monomers of sucrose?

Answer 10

Glu and fructose

Question 11

What are the two monomers of lactose?

Answer 11

Galactose and glucose

Question 12

What are the two monomers in amylose? What is the linkage here?

Answer 12

Galactose and glucose

alpha 1,4

Question 13

What are the monomers in amylopectin? What is the linkage here?

Answer 13

Glucose glucose

alpha 1,4 and alpha 1,6 branches

Question 14

What are the monomers in glycogen? What is the linkage here?

Answer 14

Glc-glc

alpha 1,6

Question 15

What are the monomers in cellulose? What is the linkage here?

Answer 15

glucose glucose

beta 1,4

Question 16

Animal is to glycogen as plant is to what?

Answer 16

Amylopectin

Question 17

Where does starch digestion begin? What enzymes? What are the bonds that are being broken?

Answer 17

Mouth
salivary endosaccharidase alpha-amylase

non-terminal alpha 1,4 linkages

Question 18

What limits the digestion of molecules in the mouth?

Answer 18

Need acidic condition of the stomach to denature stuffs

Question 19

What are the ends products of pancreatic amylase digestion? (3)

Answer 19

Maltose
Maltotriose
Alpha-limit dextrans

Question 20

Why can’t cellulose be digested?

Answer 20

Humans lack the beta-1,4 enzyme

Question 21

Lactose is hydrolyzed into glucose and galactose by what enzyme?

Answer 21

Lactase

Question 22

Maltose is hydrolyzed to two glucose molecules by what enzyme?

Answer 22

Maltase

Question 23

Sucrose is split into glucose and fructose by what?

Answer 23

Sucrase/isomaltase complex

Question 24

What is the transporter in the small intestines that picks up glucose? What the means by which this happens?

Answer 24

SGLT-1

Na/glucose transporter that utilizes Na gradient from Na/K ATPase

Question 25

What is the transporter in the small intestines that picks up fructose? What is the means by which this happens?

Answer 25

GLUT5 Facilitated diffusion

Question 26

Once inside the cell, monosaccharides are transported into | the circulation through the plasma membrane how? What is the transporter protein utilized here?

Answer 26

Through contra-luminal facilitated diffusion (GLUT2)

Question 27

What is the cause of lactose intolerance?

Answer 27

Primary lactase non-persistence is the decline in lactase as we age

Question 28

What does the breath test for Lactose intolerance measure?

Answer 28

H2 in the breath from bacterial digestion of lactose

Question 29

What are the four enzymes produced by the pancreas that pepsin activates?

Answer 29

Trypsin Chymotrypsin Elastase Carboxypeptidase

Question 30

Besides activating other enzymes, what is the role of pepsin?

Answer 30

Degrade proteins

Question 31

Where does the bulk of protein digestion occur?

Answer 31

small intestines

Question 32

What form must protein be in to be absorbed?

Answer 32

di and tri peptides (or free amino acids)

Question 33

What are the three active enzymes in the intestinal brush border that are involved in protein digestion?

Answer 33

Aminopeptidase Dipeptidase Endopeptidase

Question 34

What are the two broad categories of pancreatic proteases?

Answer 34

Endoproteases | Exoproteases

Question 35

What are the three endoproteases?

Answer 35

Trypsin Chymotrypsin Elastase

Question 36

What is the one exoprotease?

Answer 36

Carboxypeptidase

Question 37

Activation of zymogens (besides pepsin) is activated by what? Where does this occur? What is the first step in the process?

Answer 37

Endopeptidases located in the luminal plasma membrane of the intestinal enterocytes First step = conversion of trypsinogen to trypsin

Question 38

What is the role of cholecystokinin?

Answer 38

Stimulate the secretion of endopeptidases from the intestinal mucosa and trypsinogen from acinar cells of the pancreas

Question 39

What is the role of the acinar cells of the pancrease? What is the chemical signal that they respond to?

Answer 39

Secretion of trypsinogen in response to CCK release

Question 40

The digestion of most of the di and tri peptides in the intestines is completed where?

Answer 40

intracellularly in the Enterocytes

Question 41

What is issue with pancreatic duct blockage?

Answer 41

Leads to autodigestion of the pancreas via pancreatic enzymes

Question 42

What is the cause of CF?

Answer 42

mutations in the gene encoding | the CFTR protein

Question 43

What is the pancreatic issue associated with CF?

Answer 43

Reduce the production of sodium bicarbonate, leading to dehydration and thickening of the pancreatic juice/mucus. The consequence of this is to reduce the production of pancreatic digestive enzymes and in severe cases cause blockages in the lumen and the duct.

Question 44

What is the cause of celiac disease?

Answer 44

In celiac disease a peptidase defect leads to the appearance of small peptides in the intestine that are toxic to mucosal cells

Question 45

What is Hartnup disease?

Answer 45

Inability to absorb Tryptophan d/t defective transport leading to CNS symptoms and ataxia from loss of NAD

Question 46

What is the cause of cystinuria?

Answer 46

Defects in transport for Cystine, K, R, and ornithine. Causes persistent renal calculi

Question 47

The majority of the digestion of lipids is carried out by what enzyme?

Answer 47

Pancreatic lipase

Question 48

What is the apolipoprotein that provide chylomicrons their structure?

Answer 48

B48

Question 49

What are the possible causes of steatorrhea?

Answer 49

- Disruption of lipid absorption or digestion - Defective pancreatic function - Cholestyramine

Question 50

What is the enzyme that phosphorylates glucose when it enters a cell? Why does it do this?

Answer 50

Hexokinase | To keep glucose in the cell, and to start glycolysis

Question 51

What is the order of the transporters for Glucose uptake? Fructose?

Answer 51

Glucose = SGLT1 to GLUT2 Fructose = GLUT5 to GLUT2

Question 52

Where is GLUT2 found?

Answer 52

On the basolateral cellular membrane of the enterocyte

Question 53

What is the role of CCK?

Answer 53

Activates intestinal mucosal cells and pancreatic acinar cells to produce enteropeptidase and trypsinogen respectively

Question 54

What is the importance of HCl?

Answer 54

Denature proteins to make them available for enzymatic action

Question 55

What is the role of trypsin inhibitor?

Answer 55

Prevents the premature activation of trypsin in the pancrease by blocking the active site, to stop autodigestion

Question 56

Why are amino uptake disorders rare?

Answer 56

A lot of overlap between different transporters for amino acids

Question 57

Where are the two major locations of amino acid transporters?

Answer 57

Intestinal lumen | Renal membranes

Question 58

What is the major chemical reaction that pancreatic lipase is needed for?

Answer 58

Cleavage of 2FAs from a TAG to allow fats in micelles to enter cytoplasm. This is then resynthesized into TAG and put into chylomicrons

Question 59

What is the drug that binds bile salts in the intestines to lower cholesterol?

Answer 59

Cholestyramine

Question 60

What is the relationship between colon cancer, bile salt, and bacteria?

Answer 60

Some bacteria can modify bile salts into steroids, causing overproliferation of cells, and thus causing colon cancer