Met 2: Protein Overview

Question 1

What is the structure of an AA?

Answer 1

Question 2

Draw out how a peptide bond is made

Answer 2

Question 3

Compare the amount of dietary protein intake each day with the amount of protein turnover.

Answer 3

Dietary intake = 100 g protein/day

Turnover within body = 400 g protein/day

Question 4

What chemical group is found on basic AA’s?

On acidic AA’s?

Answer 4

Basic AA’s have amine group (-NH2)

Acidic AA’s have carboxylic acid (-COOH)

Question 5

What proteases are active in the GI tract? (4)

Answer 5

1. Stomach: Pepsin
2. Small intestine: Trypsinogen, chymotrypsin, carboxypeptidases

Question 6

Describe the activation of proteases in stomach and small intestine

Answer 6

• Stomach
  
  • Pepsinogen becomes pepsin with acid exposure
• Small intestine
  
  • Trypsinogen is cleaved to trypsin by enterokinase/enteropeptidase
  • Active trypsin then cleaves the other zymogens

Question 7

Which will always release free AA’s: exopeptidase or endopeptidase?

Answer 7

Exopeptidase will release free AAs because it cleaves at the ends of polypeptides

Endopeptidases will create two smaller fragments

Question 8

Describe the two methods to degrade old/misfolded/pathogenic proteins.

Answer 8

1. Polyubiquitination tags a protein for destruction by the proteasome
   
   • adding ubiq requires ATP
2. Lysosome can engulf intracellular or extracellular material
   
   • contains hydrolytic enzymes

Question 9

What method of protein degradation is used for ECM proteins?

Answer 9

Lysosome (only lysosome can break down extracellular products)

Question 10

What is the purpose of the urea cycle?

Answer 10

Get rid of ammonia (toxic) in a less toxic form (urea)