MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A patient is diagnosed with a deficiency in the production of hydrochloric acid (HCl) in the stomach. This condition would most directly impair the initial digestion of which of the following macromolecules?
- ACarbohydrates
- BNucleic acids
- CLipids
- DProteins
Show answer & explanationAnswer & explanation
Correct answer: D. Proteins
Hydrochloric acid (HCl) in the stomach creates an acidic environment essential for the denaturation of proteins and the activation of pepsinogen into pepsin. Pepsin is the primary enzyme responsible for the initial breakdown of proteins into smaller polypeptides. A deficiency in HCl would therefore directly impair protein digestion.
Why the other options are wrong
- A. Carbohydrate digestion primarily begins in the mouth with salivary amylase and continues in the small intestine, not significantly in the stomach's acidic environment.
- B. Nucleic acid digestion primarily occurs in the small intestine with pancreatic nucleases.
- C. Lipid digestion primarily begins in the small intestine, with bile and pancreatic lipases, although some minor lipid digestion can occur in the stomach via gastric lipase.
Gastric HCl Function
Hydrochloric acid secreted by parietal cells in the stomach, crucial for denaturing proteins, activating pepsinogen, and providing an optimal acidic environment for pepsin activity.
- Denatures proteins.
- Activates pepsinogen to pepsin.
- Provides optimal pH for pepsin.
- Kills ingested pathogens.
Memory trick: HCl: 'H'elps 'C'runch 'P'roteins!