Protein

Question 1

Role of proteins

Answer 1

Immune system
Structural and mechanical
Enzymes
Channels and pumps
Hormones
Transport
Fluid Balance
Acid base balance
energy

Question 2

What protein is easier to digest: Plant or animal

Answer 2

Animal

animal protein has all a essential amino acids in similar amounts that are sufficient to
meet the minimal requirements for humans

Question 3

Protein digestion process

Answer 3

1. The mouth:
   Mechanical digestion - chewing and crushing (no chemical digestion in mouth)
2. Moisten protein rich foods with salvia
3. Stomach
   From esophagus large proteins enter and mix with stomach acid (HCl)
   -Pepsinogen (inactive form of pepsin) and HCl make pepsin Hcl
   - HCl: denatures protein structure and activates pepsinogen to pepsin
   - Pepsin: cleaves proteins to smaller polypeptides and some free amino acids. These smaller peptide chains Go to small intestine and pancreas.
4. In pancreas:
   Polypeptides become tripeptides, dipeptides and amino acids through pancreatic and intestinal proteases. Pancreas also release precusors (Trypsinogen, chymotrypsinogen and procarboxypeptidase)

Then the enzymes on the small intestinal cells hydrolyze these peptides and the cells absorb them
Peptides = amino acids THROUGH intestinal tripeptidase and dipeptidase.

Trypsinogen, chymotrypsinogen and procarboxypeptidase all become activated to an active form (trypsin, chymotrypsin, carboxypeptidase) in enterocytes.

5. Small intestine:
   Trypsin: Breaks apart peptide bonds and activates chymotrypsinogen and carboxypeptidase

Chymotrypsin breaks apart peptide bonds

Carboxypeptidase breaks apart peptide bonds at the carboxyl end.

AA go through active diffusion to intestinal enterocyte.

Lecture Slide

Question 4

Nitrogen balance
Energy balance

Answer 4

Nitrogen Intake= Rate of Nitrogen expenditure

• Nitrogen balance N in = N out

Energy needs must be met to prevent amino acids from being reallocated as an energy source.

Question 5

Nitrogen balance diagram

Answer 5

Lecture Slide

Question 6

Factors affecting nitrogen balance
-causing negative nitrogen balance
-causing positive nitrogen balance

Answer 6

These factors cause negative nitrogen balance, i.e. net loss of N:
1. Decreased protein intake (over the short-term)
2. Starvation or reduced gastrointestinal function.
3. Injury, trauma or surgical operation.
4. Illness or infection or burns.
5. Some post-operative conditions.
6. Many (frequently disseminated) cancers. 7. Lactation.

These cause positive nitrogen balance i.e. net gain of N:
1. Increased protein intake (over short term)
2. Growth
3. Pregnancy
4. Recovery from illness or trauma