Biochem Ch25 Digestion And Absorption Of Basic Nutritional Constituents

Front 1

What is the role of alpha amylase in digestion?

Back 1

Alpha amylase is an enzyme that catalyzes the breakdown of specific carbohydrates (starch). Starts in the oral cavity. It breaks internal alpha 1,4 glucosidic bonds only.

Front 2

What are the differences between amylose, amylopectin and glycogen?

Back 2

Glycogen is an animal polysaccharide similar to starch but with more branch points. Start is a plant polysaccharide of glucose (glc) linked alpha-1,4 (amylose) and glc linked alpha-1,4 with branches of glc alpha-1,6 (amylopectin)

Front 3

What are the enzymes active in the stomach?

Back 3

Pepsin

Front 4

What is the Ph of the stomach?

Back 4

~ ph=2

Front 5

Where does Pepsin A cleave peptide bonds?

Back 5

Before Leu, Phe, Trp, and Tyr. IT WILL NOT CLEAVE AFTER PRO.

Front 6

What ph is Pepsin A optimally active?

Back 6

ph = 2

Front 7

What affect does the H+ content in the stomach have on proteins?

Back 7

denatures proteins and the HCL hydrolyzes peptide bonds. Additionally activates pepsin

Front 8

What is unique about pepsins?

Back 8

they are stable and optimally active at a ph ~ 2

Front 9

What secretes the inactive proenzyme pepsinogen?

Back 9

gastric chief cells

Front 10

How is pepsinogen activated?

Back 10

Pepsinogen is autoactivated by an intramolecular reaction initiated by a ph of less than 5

Front 11

What is the role of activated pepsinogen?

Back 11

Pepsin cleaves between resideues 46 and 47 of other pepsinogen molecules to proteolytically activate them at an exponential rate. Pepsin also cuts proteins into large fragments, small peptides, and free amino acids (but mostly large fragments). The small fragments activate the pancreas.

Front 12

What cells lower the ph of the stomach>

Back 12

Gastric parietal cells

Front 13

How do gastric parietal cells lower the ph of the stomach?

Back 13

They use K+/H+ exchanging ATPase (gastric proton pump) to lower the pH. (Cl- and K+ enter the stomach via channels. Bicarbonate is exchanged for Cl- in the blood)

Front 14

What is omeprazole? What is it used to treat? How does it achieve this action?

Back 14

Omeprazile (Prilosec) is a proton pump inhibitor used to treat peptic ulcer disease and gastroesophageal reflux. Under acidic conditions omeprazole converts to a sulfenamide which binds to a Cys of H+/K+ exchanging ATPase. This inhibits the proton pump from producing the HCl.

Front 15

Is the stomach essential for adequate nutrition?

Back 15

No

Front 16

How does the stomach stimulate liver and pancreas output?

Back 16

Through initiating protein and lipid hydrolysis

Front 17

What stimulates gallbladder contraction and secretion of pancreatic enzymezs?

Back 17

Cholecystokinin (CCK)

Front 18

What triggers secretin release? What is the effect of secretin?

Back 18

Secretin release is triggered by pH less than 5. Secretin stimulates secretion of pancreatic juice rich in NaHCO3 which brings the pH to ~7

Front 19

What happens to proteins as they travel through the intestinal lumen?

Back 19

Proteins are broken down into smaller particles as they travel through the intestinal lumen. The surface of the small intestine (brush border) contains enzymes which cleace oligopeptides into di- or tripeptides

Front 20

Only what kind of amino acids are transported into the blood stream?

Back 20

free amino acids

Front 21

How do amino acids get into entercytes? What happens to them once inside?

Back 21

Amino acids are transported from the luminal side into the enterocyte via transporpter. Di and tripeptides are transported via a different transporter. Once inside the enterocyte, peptides are digested to amino acids.

Front 22

What happens to carbohydrates that are in enterocytes?

Back 22

They are also broken down into smaller particles and transported into the bloodstream

Front 23

Why are lipids slow to hydrolyze?

Back 23

Because they are hydrophobic and form liquid droplets.

Front 24

Where are bile acids produced? Where are they stored?

Back 24

Bile acids are biological detergents synthesized by the liver and stored in the gall bladder

Front 25

What is the main function of bile?

Back 25

To form micelles which promote dietary fat processing

Front 26

What is another name for bile acids?

Back 26

Bile salts

Front 27

80% of all bile acids are conjugates of what compound? At the pH of the instestines, this acid is in what form?

Back 27

Cholic acid. At the pH of the intestines, the acid is deprotonated to the anionic form cholate

Front 28

What term describes the minimal concentration of bile acid necessary for micelle formation?

Back 28

Critical micellar concentration or CMC

Front 29

What does an increase in bile acid monomers lead to once CMC is reached?

Back 29

increase in the number of micelles. Additionally, bile acid monomers in a solution are in equlubrium with micelle bile acids

Front 30

What are the major driving forces for micelle formation?

Back 30

Sequestering of apolar hydrophobic groups away from water and interaction of polar groups with water. The geometry of bile acids forms a "sandwich structure"

Front 31

How do bile acids form mixed micelles? What does increasing the % of bile acid cause?

Back 31

by combining with fatty acids and phospholipids. Increasing the % of bile acid causes a more rod like micelle

Front 32

What do micelles transport?

Back 32

cholesterol and the lipid-soluble vitamins A, D, E, K (bile acid secretion is essential for their absorption)

Front 33

Dietary fatty acids and monoacylglycerols are water-soluble or insoluble?

Back 33

Slightly water soluble and virtually all absorbed by the intestines

Front 34

Dietary cholesterol is water soluble or insoluble?

Back 34

Insoluble and only ~35% absorbed

Front 35

What transporter enhances long-chain fatty acid uptake?

Back 35

FATP4

Front 36

What enhances cholesterol uptake?

Back 36

Niemann-Pick C1-like protein channel

Front 37

What is the size requirement for fatty acid uptake via diffusion through the enterocyte membranes?

Back 37

less than 10 carbon length fatty acid chains (passes directly into the portal bloodstream)

Front 38

What happens to long-chain fatty acids in the enterocytes?

Back 38

Transported to the endoplasmic reticulum where they are converted into triacylglycerols (TAGs). Cholesterol is esterified and combined with phospholipids, apolipoproteins, and TAGs to form chylomicrons which are released into lacteals, the thoracic duct, and the left subclavian vein

Front 39

How are bile acids synthesized?

Back 39

Bile acids are synthesized in the liver from cholesterol

Front 40

How much new bile acid is synthsized per day?

Back 40

~ 0.8 g which is equal to the amount lost through excretion

Front 41

How much bile acid is secreted by the liver each day?

Back 41

~ 25 g

Front 42

What is the entire bile acid content of the body?

Back 42

~ 4g. For the liver to secrete ~ 25 g of bile acid each day, the cycle of secretion and absorption occurs between 4-10 times.

Front 43

What is the complete pathway of the enterohepatic circulation?

Back 43

Bile acid travels from the liver to the gallbladder to the duodenum, is reabsorbed in the ileum and cecum, returns to the liver through the portal vein

Front 44

How are intestinal endocrine cells triggered and what do they release?

Back 44

Intestinal endocrine cells are triggered by polypeptides, oligopeptides, and amino acids. The cell releases CCK (cholecystokinin) and secretin

Front 45

How are pancreatic acinar cells activated? What do they release?

Back 45

By CCK and secretin. They release trypsinogen

Front 46

How is trypsinogen activated?

Back 46

Trypsinogen is cleaved by enteropeptidase to trypsin. Trypsin is then able to cleave more trypsinogen or it can act on chymotrypsinogen, proelastase, or procarboxypeptidase - all proenzymes responsible digestive cleaving of amino chains

Front 47

What is a gastric enzyme that digest peptides?

Back 47

pepsin

Front 48

What are four pancreatic enzymes that digest peptides?

Back 48

trypsin, chymotrypsin, elastase, carboxypeptidase

Front 49

What is the fragment size of digested proteins at the point they enter the blood stream?

Back 49

Only free amino acids are transported into the blood stream

Front 50

What are the four enzymes discussed that breakdown carbohydrates?

Back 50

Amylase, lactase, alpha-glucosidases, and sucrase

Front 51

What are the substrates and products for amylase?

Back 51

Amylase cleaves starch with the alpha 1,4 bonds between glucose chains to leave chains of alpha 1,6 bonded glucose. These products are Maltose, Maltotriose, and alpha-limit dextrins

Front 52

What are the substrates and products for alpha-glucosidases?

Back 52

Substrates are maltose, maltotriose, and alpha-limit dextrin. The product is glucose

Front 53

What are the substrates and products for sucrase?

Back 53

The substrate is sucrose and the products are fructose and glucose

Front 54

What are the substrates and products for lactase?

Back 54

The substrate is lactose and the products are galactose and glucose

Front 55

What size fragment of digested carbohydrate enters the blood stream?

Back 55

monosaccarides only

Front 56

What is the role of gastric lipase in lipid digestion?

Back 56

Digests 30% of Triacylglycerols into smaller emulsion droplets

Front 57

What is the role of pancreatic lipase and colipase on lipid digestion?

Back 57

Pancreatic lipase aided by colipase is the major enzyme for lipid hydrolysis