digestion - proteins

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

Question 9

list pancreatic exocrine and what do they do

Answer 9

Question 10

what are the actions of zymogens

Answer 10

Question 11

what is an endopeptidase

Answer 11

enzyme that breaks down peptide bonds within the interior of the polypeptide chain

Question 12

what is an exopeptidase

Answer 12

enzymes that cleave peptide bonds at the end of polypeptide chains

Question 13

what is a protease

Answer 13

an enzyme that conducts proteolysis

Question 14

name the 6 groups of proteases

Answer 14

• serine protease (trypsin, chymotrypsin)
• threonine proteases
• cycteine proteases
• aspartic acid proteases
• metalloproteases
• glutamic acid proteases

Question 15

is trypsin an endopeptidase or and exopeptidase

Answer 15

serine endopeptidase

Question 16

what are serine endopeptidases

Answer 16

• synthesized by pancreatic acinar cells and secreted into the small intestine
• chymotrypsin cleaves bonds following a large hyrdophobic amino acid residue
• trypsin cleaves bonds after a positively charged amino acid residue
• elastase cleaves bonds after a small neutral amino acid residue (alanine, glycine, valine)

Question 17

discuss how protein is digested

Answer 17

1. denatured by stomach acid
2. passes into small intestine
3. luminal phase = bond specific proteases hydrolyse protein to short chain peptides
4. membranous phase = hydrolysed further to mainly di/tripeptides but some free amino acids
5. specific membrane proteins then transport across gut wall by secondary active transport

Question 18

whats an aminopeptidase

Answer 18

• attack the amino terminal of peptides secreted from the small intestine
• aka exopeptidases

Question 19

what are the 2 routes of amino acid transport

Answer 19

1. peptide transporter with high affinity for di and tri peptides
2. single amino acid transport from the intestinal lumen is again an active process that involves a Na dependent carrier mediated cotransport system similar to that of glucose

Question 20

what are the groups of amino acid transporters

Answer 20

• neutral amino acids, transported by systems like System A and ASC
• acidic amino acids transported by EAATs
• basic amino acids and cysteine transported by system y
• di and tripeptides treansported by peptide transporter