Protein digestion

Question 1

What are the cells of the pancreas and what do they produce?

Answer 1

alpha cells - glucagon
beta cells - insulin
delta cells - somatostatin
acini cells - digestive enzyme (secreted as zymogens)

Question 2

What pancreatic enzymes digest protein?

Answer 2

Trypsin
chymotrypsin
elastase
pro-carboxypeptidase

Question 3

What causes zymogens from the pancreas to be converted into active enzymes?

Answer 3

activated in the duodenum by enteropeptidase

Question 4

What are exopeptidases and endopeptidases?

Answer 4

Exopeptidases - detach the terminal amino acids from polypeptide e.g., aminopeptidases
Enodpeptidases - hydrolye internal peptide bonds of a protein e.g., trypsin, pepsin, elastase

Question 5

What is the action of serine endoproteases?

Answer 5

Synthesised by pancreatic acinar cells
secreted into SI
Chymotrypsin - cleaves bond following large hydrophobic amino acid residue e.g. tyrosine, phenylalanine
Trypsin - cleaves bonds after a +ve charged amino acid residue e.g., aginine and lysine
Elastase - cleaves bonds after a small neutral amino acid residue e.g., alanine, glycine, valine

Question 6

Describe the process of protein digestion

Answer 6

Protein denatured by stomach acid
Passes to SI
Luminal phase - bond-specific proteases hydrolyse protein to short chain peptides
Membranous phase - hydrolysed further to di/tripeptides and some free amino acids
Specific membrane proteins transported across gut wall by secondary active transport

Question 7

What is the action of aminopeptidases?

Answer 7

attack the amino terminal of peptides secreted from the SI
exopeptidases

Question 8

Describe the routes of amino acid transport

Answer 8

1. peptide transporter
2. single amino acid transport from instestinal lumen is an active process that involves Na+ dependent carrier-mediated cotransport system. Selective carrier systems are present for certain groups of amino acids:
   - neutral AAs
   - acidic (dicarboxylic) AAs
   - imino amino acids
   - basic amino acids