Protein Digestion

Question 1

describe the general digestion of sugars

Answer 1

1. alpha amylase in the saliva begins starch breakdown
2. travels to stomach where sucrose and lactose begins to break down through alpha dextrins
3. travels to small intestine where pancreatic enzymes are released to break down tri and oligosaccharides, maltose and isomaltose
4. maltase, isomaltase, sucrase, and lactase break down maltose, isomaltose, sucrose, and lactose
5. intestinal brush border absorbs glucose, fructose, and galactose.
6. fiber is excreted in the feces.

Question 2

describe the general digestion of fatty acids

Answer 2

1. triacylglycerol enters the mouth and passes to the stomach.
2. bile salts surround the TG, making a micelle, and the pancreas secretes colipase and lipase.
3. colipase activates lipase to break down the micelle into fatty acids plus 2-monoacylglycerol in the intestine
4. bile salts surround the fatty acids and 2-MG to make another micelle.
5. intestinal brush border cells take up the FA and 2-MG via peristalsic contractions and make it into a nascent chylomicron by adding apoB48 and phospholipids.
6. bile salts are recycled into the blood.
7. chylomicrons are released into the lymph and then brought into the blood.

Question 3

describe the general digestion of proteins

Answer 3

REQUIRES ZYMOGENS

1. food is masticated and brought into the stomach.
2. stomach releases HCl and pepsinogen.
3. low pH of stomach activates pepsinogen to pepsin and protein is cleaved in the middle and through acid hydrolysis.
4. peptides move into the small intestine where the pancreas secretes HCO3, trypsinogen, chymotripsinogen, proelastase, and procarboxypeptidases A&B.
5. enteropeptidases in the gut wall converts trypsinogen to trypsin, and trypsin converts the other pancreatic enzymes to chymotrypsin, elastase, carboxypeptidase A&B.
6. these di and tripeptides and amino acids are taken up into the brush border epithelial cells and further broken down to amino acids.
7. amino acids then secreted directly into the blood.

Question 4

what converts pepsinogen/

Answer 4

low pH in the stomach converts to pepsin

Question 5

what converts trypsinogen

Answer 5

enteropeptidase in the gut wall concerts to trypsin

Question 6

what converts chymotrypsinogen

Answer 6

trypsin converts to chymotrypsin

Question 7

what converts proelastase

Answer 7

trypsin converts to elastase

Question 8

what converts procarboxypeptidase A&B

Answer 8

trypsin converts to carboxypeptidase A&B

Question 9

what is meant by protease specificity

Answer 9

1. pancreatic enzymes are activated in specific parts of body
2. the proteases recognize specific amino acid sequences and directionality and cleave and these specific sites. if one AA or direction is wrong, they will NOT cleave.

Question 10

describe how amino acids are taken up into the blood from the intestinal lumen

Answer 10

amino acid must enter brush border cells through a sodium symporter, that transports an AA with a sodium molecule going with its concentration gradient. then, AA travels through a facilitated transporter down its concentration gradient to the portal vein.

Question 11

explain why amino acids have to be transported with sodium into the intestinal cells

Answer 11

the intestinal lumen is relatively large, and has a low concentration. the intestinal cell itself is relatively small and has a high concentration. therefore, the AA would be traveling against the concentration gradient. therefore, it needs to hitch a ride on a sodium, which is traveling down its concentration gradient.

Question 12

how is Na recycled after being used to bring AA in?

Answer 12

Na leaves the cell through the NA K ATP active transporter, where NA leaves the cell and K enters the cell, using an ATP.