Protein Digestion

Question 1

What two important products are found in the stomach that participate in protein breakdown?

Answer 1

Acid denatures proteins, pepsin produces peptide segments.

Question 2

How is pepsinogen activated to pepsin?

Answer 2

Pro-peptide fragment is cleaved at acidic pH to activate the enzyme.

Question 3

Which cells make pepsinogen?

Answer 3

Chief cells and pancreatic acinar cells.

Question 4

What does enteropeptidase do to trypsinogen?

Answer 4

Cleaves it to trypsin. Trypsin can then cleave trypsinogen (pos. feedback)

Question 5

How does the body deal with trypsinogen that is accidentally activated in the pancreas?

Answer 5

Trypsin inhibitor.

Question 6

Name two ways in which trypsin inhibitor can be insufficient, resulting in pancreatitis.

Answer 6

1. Duct blockage - inhibitor is overwhelmed.

2. Mutant trypsin - inhibitor cannot bind to mutated protein.

Question 7

Are AAs actively transported into the intestinal cells?

Answer 7

Yes, with a Na+ linked transporter similar to glucose.

Question 8

What is cystinuria?

Answer 8

Defective cysteine transporter. Cannot resport cysteine from presumptive urine. Cysteine has low solubility and this results in stones in the PCT.

Question 9

What other AA is transported using the cysteine transporter?

Answer 9

Lysine

Question 10

What is Hartnup disease?

Answer 10

Defective tryptophan transporter. Results in abnormal excretion into urine and abnormal intestinal absorption. Tryptophan is a precursor to niacin, niacin deficiency –> NAD+ deficiency –> Pellagra (D3 symptoms)

Question 11

What are three non-dietary AA sources?

Answer 11

1. Lysosomal system
2. Digestive enzyme turnover
3. Ubiquitin/proteasome pathway (major)

Question 12

How long are the AA fragments that proteasomes poop out?

Answer 12

7-10 AAs long

Question 13

What are the names of the enzymes that add ubiquitin to proteins?

Answer 13

E1, E2, E3

Question 14

What enzyme recycles ubiquitin?

Answer 14

Deubiquitinase enzyme

Question 15

What are the two choices for proteins that are pooped out of the proteasome?

Answer 15

Go to MHC I or get incorporated into new AAs.

Question 16

What ubiquitination signal means that the protein will be longest-lived?

Answer 16

Methionine on N terminus

Question 17

How does HPV E6 work?

Answer 17

E6 binds to p53, which attracts E6-AP, which adds ubiquitin to p53 —> degradation of p53

Question 18

What is the Parkin mutation involved with?

Answer 18

Decreased ability to poly-ubiquitinate proteins. Proteins build up (Lewy bodies) –> neurodegeneration.

Question 19

Aside from Parkin mutation, what is another enzyme linked to Parkinson’s disease involved in UPP?

Answer 19

Deubiquitinase, which recycles ubiquitin, is defective, so ubiquitinated proteins build up.

Question 20

What are the essential AAs?

Answer 20

Phenylalinine, valine, threonine, tryptophan, isoleucine, methionine, histidine, arginine, leucine, lysine
(PVT TIM HALL)

Question 21

What is kwashiorkor?

Answer 21

Insufficient protein in diet. First-child-after-the-second-child-is-born-and-is-now-not-getting-enough-protein-from-mother’s-milk disease.

Question 22

Name four enzymes made in the pancreas.

Answer 22

1. Trypsinogen
2. Chymotrypsinogen
3. Proelastase
4. Procarbodypeptidases

Question 23

What is the difference between carboxypeptidases and aminopeptidases?

Answer 23

Carboxypeptidases cleave at carboxy end, aminopeptidases cleave at N end.