Protein Digestion

Protein Digestion

To the tune of “Life on Mars” by David Bowie

[Verse 1]
Digestion of polypeptides
Facilitated by enzymes
Chief cells secrete pepsinogen
As an inactive zymogen
It is partially activated
By the lower gastric pH
Parietal cells secrete protons
In initiating this change

[Pre-Chorus]
Pepsin’s an endopeptidase
Splitting polypeptide chains
At internal peptide bonds
It’s inactivated by the

[Chorus]
Alkaline small intestine
Made less acidic by bicarbonate
Raising the pH
The pancreas releases bile salts and enzymes
Trypsinogen, an endopeptidase
Activated by enterokinase
Protein digestion

[Verse 2]
There are brush border enzymes
Lining the microvilli
Including enterokinase
Which initiates a cascade
Trypsin activates zymogens
Including chymotrypsin
And carboxypeptidase
By proteolytic activation

[Pre-Chorus]
Amino acids are absorbed
Through the process of cotransport
With cationic sodium
Reliant on the action of 

[Chorus]
The sodium-potassium pump
It requires at least four
Proteins for cotransport
Of all 20 amino acids
They diffuse out of the cell
Through basolateral channels
Protein absorption