Digestion And Absorption Of Proteins

Question 1

Protein digestion

Answer 1

Catabolic pathway

-Proteins are large polypeptides made up of Amino acids (AAs)
-AAs binds together by peptide bond
-The bond that is broken during digestion of Proteins
are called peptide bond

Question 2

Protein digestion in the stomach: production of pepsin

Answer 2

-Chief cells → pepsinogen → activate → Pepsin

-Activation of Pepsinogen to pepsin requires an acidic environment
-Parietal cells → HCL → Decrease the pH → Acidic Environment 1.8-3.5 → stimulate the conversion of pepsinogen into pepsin
-↑pH → pepsin inactivated

Question 3

Protein digestion in the stomach: function of pepsin

Answer 3

-Pepsin stimulates the conversion of pepsinogen into pepsin (=Auto activator)

-Pepsin converts large polypeptide → smaller polypeptides
-Targets aromatic amino acids → Break bonds on carboxyl side
-Tyrosine
-Phenylalanine
-Tryptophan

Question 4

Source of bicarbonate

Answer 4

Mucosal cells

Question 5

Function of bicarbonate

Answer 5

Neutralizes gastric acids

Question 6

Bicarbonate stimulate by

Answer 6

Secretin

Question 7

Source of CCK

Answer 7

I cells (duodenum, jejunum)

Question 8

Functions of CCK

Answer 8

⬆️Contraction of the gallbladder
↑ Secretion of pancreatic Enzymes
↑Relaxation of the sphincter of Oddi

Question 9

CCK stimulated by

Answer 9

Postprandial: fatty acids and amino acids entering the small intestine

Question 10

Source of secretin

Answer 10

S cells (duodenum)

Question 11

Functions of secretin

Answer 11

↑Pancreatic secretion of bicarbonate
↑Secretion of bile

Question 12

Secretin stimulated by

Answer 12

Postprandial: ↑ gastric acid and fatty acids in the duodenum

Question 13

Source of GIP

Answer 13

K cells (Duodenum, jejunum)

Question 14

Functions of GIP

Answer 14

↑ Insulin secretion
↓ Secretion of gastric acid

Question 15

GIP stimulated by

Answer 15

Postprandial: fatty acids, glucose, amino acids entering small intestine

Question 16

GIP

Answer 16

“Glucose-dependent insulinotropic peptide”

“Gastric inhibitory polypeptide”

Question 17

Production of pancreatic processes

Answer 17

-CCK= Cholecystokinin
-Stimulate acinar cells to produce Proteases
-Relaxes the Sphincter of Oddi → ejection of the Proteases to the duodenum

-Proenzymes (Inactive)
-Trypsinogen
-Chymotrypsinogen
-Procarboxypeptidase
-Proelastase

Question 18

Activation of pancreatic proteases

Answer 18

-Enterokinase in the epithelial cells of the lumen → brush border enzyme → activate trypsinogen → trypsin

-Trypsin stimulates the activation of proenzymes

1) Trypsinogen → trypsin
2) Chymotrypsinogen → chymotrypsin
3) Procarboxypeptidase → carboxypeptidase (A&B)
4) Proelastase → elastase

Question 19

Function of pancreatic proteases: trypsin

Answer 19

-Small polypeptide → Cleave peptide bonds on the
carboxyl side where there are Lysine and Arginine → tripeptide, dipeptide

-Exception they cannot hydrolyze the bond if there is Proline next to Lysine or Arginine

Question 20

Function of pancreatic proteases: chymotrypsin

Answer 20

Small polypeptide→ same as pepsin → Cleave peptide bonds on the carboxyl side where there are Tyrosine, Phenylalanine, Tryptophan → tripeptide, dipeptide

Question 21

Function of pancreatic proteases: carboxypeptidase

Answer 21

Small polypeptide→ act on carboxyl end→ AA, dipeptide, tripeptide

Question 22

Function of pancreatic proteases: elastase

Answer 22

Small polypeptide→ act on carboxyl end → AA, dipeptide, tripeptide

Question 23

Brush border enzymes of small intestin

Answer 23

Dipeptidase

Aminopeptidase

Question 24

Location of brush border enzymes

Answer 24

-Enterocytes→ epithelial cell found in the small intestine

-Most of the absorption occurs in the small intestine

-Structural Modifications that increase surface area in the small intestine →↑Digestion and ↑Absorption
-Circular Folds
- Villi
-Microvilli
-Enterocyte → little cytoplasmic extensions → increase the surface area for chemical digestion and absorption → microvilli → high concentration of brush border enzymes

Question 25

Absorption of protein: apical membrane: transporters

Answer 25

-AA Transporters -Dipeptide Transporters -Tripeptide Transporters -Na+ /H+ Antiporter

Question 26

Absorption of proteins: apical membrane: dipeptides and tripeptides uptake mechanism

Answer 26

-Dipeptide Transporters = H+ / Dipeptide cotransporter -Tripeptide Transporters= H+ / Tripeptide cotransporter -Dipeptide and tripeptide uptake is an active process driven by a proton gradient. -Na+ /H+ Antiporter → brings in proton in exchange of Na+ -Proton used for the transportation of the Dipeptide and tripeptide→ Symport mechanism

Question 27

Absorption of proteins: apical membrane: AAs Uptake Mechanism

Answer 27

-AA Transporters = Na+ / AA cotransporter -Na+/K+ / ATPase →↓Na+ in the enterocyte -Na+/K+ ATPase on the basal membrane → pump 3 Na+ outand2K+ in+utilizinganATP→↓Na+ →Na+ in lumen >> Na+ in the enterocyte → AAs follow Na+ from lumen to enterocyte -Secondary active transport → Driving Force is sodium concentration gradient -Sodium moves down its concentration gradient into the cell, taking AA -AA move against its concentration gradient

Question 28

Absorption of proteins: enterocyte

Answer 28

Enzyme in the enterocyte → Intracellular Peptidase cleave dipeptide, tripeptide → AAs

Question 29

Absorption of proteins: basolateral membrane

Answer 29

-Transporter: AA transporters -Mechanism: -AAs move out of the cell through Facilitated diffusion mechanism → capillaries → veins → hepatic portal vein → liver -In the liver the AAs → Protein Synthesis -↑ Insulin release in the fed state → Enhance protein synthesis and AAs Uptake

Question 30

Pepsinogen

Answer 30

Activating agent: enteropeptidase and trypsin Active enzyme: pepsin Location: stomach Function: cleaves bonds involving Phenylalanine, Tyrosine, and Tryptophan Product: peptides, oligopeptides

Question 31

Trypsinogen

Answer 31

Activating agent: enteropeptidase and trypsin Active agent: trypsin Location: pancreas secretion to Duodenum Function: cleaves bonds of the C-terminal of Lysine and Arginine Product: tripeptide, dipeptide

Question 32

Chymotrypsinogen

Answer 32

Activating agent: trypsin Active enzymes: chymotrypsin Location: pancreas secretion to Duodenum Function: cleaves bonds involving Phenylalanine, Tyrosine, and Tryptophan Product: tripeptide, dipeptide

Question 33

Pro-elastase

Answer 33

Activating agent: trypsin Active enzyme: elastase Location: pancreas secretion to Duodenum Function: Cleaves bonds, from C-Terminal Product: AAs, tripeptide, dipeptide

Question 34

Pro-carboxypeptidase

Answer 34

Activating agent: trypsin Active enzyme: carboxypeptidase (A, B) Location: pancreas secretion to Duodenum Function: cleaves bonds from C-Terminal Product: AAs, dipeptide, tripeptide

Question 35

Aminopeptidase

Answer 35

Location: intestinal mucosa Function: Cleaves unspecific end AAs from N- terminal Product: AAs

Question 36

Dipeptidase

Answer 36

Location: intestinal mucosa Function: cleaves dipeptides Product: AAs