Role of pepsin in protein digestion MCQs With Answer

Role of pepsin in protein digestion MCQs With Answer

Pepsin is a key gastric enzyme that initiates protein digestion by cleaving peptide bonds in the acidic environment of the stomach. For B. Pharm students, understanding pepsin’s origin as pepsinogen from chief cells, activation by low pH, specificity for aromatic amino acids, and inhibition by pepstatin and antacids is essential for pharmacology and biochemistry. This topic links enzymology, drug interactions, clinical implications such as peptic ulcer disease, and formulation considerations for protein drugs. These concepts help in designing drug regimens and interpreting digestive pathology. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which cell type in the stomach secretes pepsinogen, the zymogen of pepsin?

• Parietal cells
• Mucous neck cells
• Chief (zymogenic) cells
• Enterochromaffin-like cells

Correct Answer: Chief (zymogenic) cells

Q2. What is the primary stimulus for conversion of pepsinogen to active pepsin?

• Alkaline pH in the small intestine
• Presence of dietary lipids
• Low gastric pH (acidic environment)
• Enteric hormones like secretin

Correct Answer: Low gastric pH (acidic environment)

Q3. Pepsin is classified as which type of protease?

• Serine protease
• Cysteine protease
• Aspartic protease
• Metalloprotease

Correct Answer: Aspartic protease

Q4. Which amino acid residues are preferentially cleaved by pepsin?

• Basic residues like Lys and Arg
• Aromatic residues like Phe, Trp, Tyr
• Small residues like Gly and Ala
• Acidic residues like Asp and Glu

Correct Answer: Aromatic residues like Phe, Trp, Tyr

Q5. What is the optimal pH range for pepsin activity?

• pH 1.5–3.5
• pH 5.5–7.0
• pH 7.5–9.0
• pH 9.5–11.0

Correct Answer: pH 1.5–3.5

Q6. Which drug class can reduce pepsin activity indirectly by increasing gastric pH?

• Proton pump inhibitors (PPIs)
• Beta-blockers
• Loop diuretics
• Statins

Correct Answer: Proton pump inhibitors (PPIs)

Q7. Pepstatin is best described as which of the following?

• A competitive inhibitor of serine proteases
• A specific inhibitor of aspartic proteases like pepsin
• An activator of pepsinogen conversion
• An antacid used clinically

Correct Answer: A specific inhibitor of aspartic proteases like pepsin

Q8. Pepsinogen is converted to pepsin by which chemical process?

• Phosphorylation
• Proteolytic cleavage
• Glycosylation
• Methylation

Correct Answer: Proteolytic cleavage

Q9. Which organelle is primarily involved in synthesizing and packaging pepsinogen in chief cells?

• Mitochondria
• Rough endoplasmic reticulum and Golgi apparatus
• Lysosomes
• Peroxisomes

Correct Answer: Rough endoplasmic reticulum and Golgi apparatus

Q10. What is the effect of pepsin on dietary proteins?

• Converts them entirely into free amino acids in the stomach
• Initiates proteolysis producing large polypeptides and oligopeptides
• Denatures proteins without cleavage
• Targets only carbohydrate groups

Correct Answer: Initiates proteolysis producing large polypeptides and oligopeptides

Q11. Which of the following best describes the active site residues of pepsin?

• Two serine residues forming a catalytic dyad
• Two cysteine residues in a catalytic triad
• Two aspartic acid residues forming a catalytic dyad
• A zinc ion coordinating catalysis

Correct Answer: Two aspartic acid residues forming a catalytic dyad

Q12. How does pepsin contribute to innate immunity in the stomach?

• By producing hydrochloric acid
• By digesting bacterial proteins and disrupting pathogens
• By secreting antibodies
• By neutralizing bile salts

Correct Answer: By digesting bacterial proteins and disrupting pathogens

Q13. Which physiological factor enhances pepsinogen secretion?

• Somatostatin release
• Gastrin and vagal stimulation
• High intestinal pH
• Secretin from duodenal S cells

Correct Answer: Gastrin and vagal stimulation

Q14. In which condition would pepsin activity be expected to be reduced?

• Hyperchlorhydria (excess acid)
• Hypochlorhydria (reduced acid)
• Normal fasting stomach
• Postprandial acidic surge

Correct Answer: Hypochlorhydria (reduced acid)

Q15. Which laboratory assay principle is commonly used to measure pepsin activity?

• Chromogenic peptide substrates and spectrophotometry
• Radioactive lipid incorporation
• ELISA for DNA binding
• pH titration only

Correct Answer: Chromogenic peptide substrates and spectrophotometry

Q16. Which peptide bond preference is characteristic of pepsin cleavage?

• Peptide bonds involving positively charged residues
• Peptide bonds near aromatic or large hydrophobic residues
• Peptide bonds adjacent to phosphorylated residues
• Peptide bonds only in N-terminal region

Correct Answer: Peptide bonds near aromatic or large hydrophobic residues

Q17. Pepsin remains active in the stomach but is inactivated in which region due to pH changes?

• Duodenum where pH rises due to bicarbonate
• Esophagus due to neutral pH
• Colon due to bacterial proteases
• Oral cavity due to saliva

Correct Answer: Duodenum where pH rises due to bicarbonate

Q18. Which clinical condition can result from excess acid and pepsin damaging the gastric or esophageal mucosa?

• Peptic ulcer disease and reflux esophagitis
• Gallstones
• Crohn’s disease
• Ulcerative colitis

Correct Answer: Peptic ulcer disease and reflux esophagitis

Q19. Which of the following molecules is a natural inhibitor of pepsin in the stomach lumen?

• Mucous bicarbonate barrier and neutral pH at mucosal surface
• Gastrin hormone
• Intrinsic factor
• Enterokinase

Correct Answer: Mucous bicarbonate barrier and neutral pH at mucosal surface

Q20. Which structural feature of pepsin contributes to its resistance to self-digestion at low pH?

• Glycosylation shielding the active site
• Zymogen propeptide domain that blocks active site until cleavage
• Disulfide bonds preventing unfolding
• Metal cofactors stabilizing the structure

Correct Answer: Zymogen propeptide domain that blocks active site until cleavage

Q21. Which therapeutic application could target pepsin activity?

• Use of pepstatin-like compounds to study aspartic protease mechanism
• Administration of exogenous pepsin for peptic ulcers
• Use of pepsin as an antihypertensive
• Using pepsin to chelate heavy metals

Correct Answer: Use of pepstatin-like compounds to study aspartic protease mechanism

Q22. Pepsinogen secretion is decreased by which of the following?

• Vagal nerve stimulation
• Histamine acting on H2 receptors
• Somatostatin release
• Gastrin hormone

Correct Answer: Somatostatin release

Q23. What happens to protein tertiary structure in the stomach that facilitates pepsin action?

• Proteins are glycosylated
• Proteins are denatured by acidic pH
• Proteins are phosphorylated
• Proteins form disulfide-stabilized aggregates

Correct Answer: Proteins are denatured by acidic pH

Q24. Which of these is NOT a property of pepsin?

• Active at highly acidic pH
• Synthesized as an inactive zymogen
• Requires a metal ion for activity
• Preferentially cleaves near aromatic residues

Correct Answer: Requires a metal ion for activity

Q25. Pepsin plays a role in oral pharmaceutical formulations by:

• Enhancing absorption of intact proteins in the stomach
• Contributing to degradation of orally administered protein drugs
• Neutralizing enteric coatings
• Acting as a systemic enzyme after absorption

Correct Answer: Contributing to degradation of orally administered protein drugs

Q26. Which of the following is a common experimental substrate used to assay pepsin?

• Hemoglobin or casein
• Lipase-specific triglycerides
• DNA plasmids
• Glucose

Correct Answer: Hemoglobin or casein

Q27. Which pharmacological agent directly neutralizes gastric acid and can reduce pepsin activity?

• Antacids like magnesium hydroxide
• ACE inhibitors
• SSRIs
• Beta-agonists

Correct Answer: Antacids like magnesium hydroxide

Q28. Which statement about pepsinogen gene expression is correct?

• Pepsinogen is expressed primarily in hepatocytes
• Pepsinogen genes are expressed in gastric chief cells
• Pepsinogen is encoded by mitochondrial DNA
• Pepsinogen expression is restricted to pancreatic acinar cells

Correct Answer: Pepsinogen genes are expressed in gastric chief cells

Q29. During neonatal digestion, an enzyme related to pepsin that aids milk digestion is called:

• Trypsin
• Rennin (chymosin)
• Pancreatic lipase
• Amylase

Correct Answer: Rennin (chymosin)

Q30. Which structural class best describes pepsin’s fold?

• Alpha/beta barrel
• Mostly beta-sheet typical of aspartic proteases
• Zinc-finger motif
• Transmembrane helix

Correct Answer: Mostly beta-sheet typical of aspartic proteases

Q31. If a patient is on chronic PPI therapy, what is a likely effect on pepsin-mediated protein digestion?

• Increased pepsin activity due to rebound acid
• Decreased pepsin activity due to higher gastric pH
• No change since PPIs do not affect stomach pH
• Pepsin becomes more specific for basic residues

Correct Answer: Decreased pepsin activity due to higher gastric pH

Q32. What is the approximate molecular weight of mature pepsin A?

• ~10 kDa
• ~34 kDa
• ~100 kDa
• ~250 kDa

Correct Answer: ~34 kDa

Q33. Which peptide bond location is least likely to be cleaved by pepsin?

• Bond adjacent to phenylalanine
• Bond adjacent to tryptophan
• Bond adjacent to proline in certain contexts
• Bond adjacent to tyrosine

Correct Answer: Bond adjacent to proline in certain contexts

Q34. Which lab finding would indicate reduced pepsin activity in a gastric fluid sample?

• Low pH and high proteolysis
• High pH and low proteolysis of protein substrates
• High pepsinogen but high proteolysis
• Normal pH with increased digestion

Correct Answer: High pH and low proteolysis of protein substrates

Q35. Which of the following is true about pepsin specificity compared to pancreatic proteases?

• Pepsin is more active at basic pH than trypsin
• Pepsin prefers hydrophobic/aromatic residues, while trypsin prefers basic residues
• Both pepsin and trypsin have identical specificity
• Pancreatic proteases function only in the stomach

Correct Answer: Pepsin prefers hydrophobic/aromatic residues, while trypsin prefers basic residues

Q36. Which molecular change converts pepsinogen to pepsin?

• Cleavage of the N-terminal propeptide revealing the active site
• Addition of a metal ion cofactor
• Attachment of a lipid anchor
• Cross-linking with mucin

Correct Answer: Cleavage of the N-terminal propeptide revealing the active site

Q37. How does pepsin activity influence bioavailability of orally administered peptide drugs?

• Pepsin enhances absorption by transporting peptides across mucosa
• Pepsin degrades peptide drugs, reducing oral bioavailability
• Pepsin converts peptides to prodrugs increasing bioavailability
• Pepsin specifically glycosylates peptide drugs to protect them

Correct Answer: Pepsin degrades peptide drugs, reducing oral bioavailability

Q38. Which dietary component can protect some proteins from pepsin digestion?

• Denaturation by heat
• Cross-linking (e.g., by tannins) or encapsulation
• Presence of simple sugars
• High salt concentration only

Correct Answer: Cross-linking (e.g., by tannins) or encapsulation

Q39. Which experimental inhibitor would you use to specifically block pepsin in a biochemical study?

• PMSF (phenylmethylsulfonyl fluoride)
• Pepstatin
• EDTA
• Iodoacetamide

Correct Answer: Pepstatin

Q40. In the context of gastric reflux, why is pepsin considered harmful to the laryngeal mucosa?

• Pepsin is inactive outside the stomach and harmless
• Pepsin can remain active at mildly acidic pH and damage laryngeal proteins
• Pepsin converts mucus to acid
• Pepsin stimulates bacterial overgrowth only

Correct Answer: Pepsin can remain active at mildly acidic pH and damage laryngeal proteins

Q41. What is a zymogen?

• An active enzyme requiring no further processing
• An inactive precursor of an enzyme, e.g., pepsinogen
• A cofactor for enzymatic reactions
• A type of gastric hormone

Correct Answer: An inactive precursor of an enzyme, e.g., pepsinogen

Q42. Which ion pump is primarily responsible for creating the acidic environment needed for pepsin activation?

• Sodium-potassium ATPase
• H+/K+ ATPase (proton pump) in parietal cells
• Calcium ATPase
• CFTR chloride channel

Correct Answer: H+/K+ ATPase (proton pump) in parietal cells

Q43. Which clinical test might reflect pepsin involvement in laryngopharyngeal reflux?

• Pepsin detection in saliva or throat swab
• Fecal occult blood test
• Serum amylase measurement
• Urine protein electrophoresis

Correct Answer: Pepsin detection in saliva or throat swab

Q44. Pepsin displays endopeptidase activity. What does this mean?

• It cleaves peptide bonds at the ends of polypeptides only
• It cleaves internal peptide bonds within polypeptide chains
• It removes single amino acids from N-terminus
• It only removes C-terminal amino acids

Correct Answer: It cleaves internal peptide bonds within polypeptide chains

Q45. Which factor could increase gastric pepsin activity during a meal?

• Higher gastric pH due to bicarbonate
• Increased vagal tone and gastrin secretion
• Somatostatin release inhibiting secretion
• Use of H2 receptor antagonists

Correct Answer: Increased vagal tone and gastrin secretion

Q46. Which statement about pepsin and protein allergenicity is correct?

• Pepsin digestion always increases allergenicity of proteins
• Resistance to pepsin digestion may correlate with increased oral allergenicity
• Pepsin converts allergens to harmless peptides in all cases
• All proteins are equally susceptible to pepsin

Correct Answer: Resistance to pepsin digestion may correlate with increased oral allergenicity

Q47. Which therapeutic approach reduces both acid and pepsin-mediated mucosal injury in reflux disease?

• Prokinetic agents only
• Acid suppression with PPIs plus alginate/antacid to bind refluxate
• Systemic steroids
• Topical antibiotics

Correct Answer: Acid suppression with PPIs plus alginate/antacid to bind refluxate

Q48. In recombinant protein formulation, which strategy helps protect a peptide from pepsin degradation?

• Oral immediate-release tablet without excipients
• Enteric coating and protease inhibitors in the formulation
• Administering with acidic beverages to increase pepsin activity
• Avoiding any coating to enhance exposure to pepsin

Correct Answer: Enteric coating and protease inhibitors in the formulation

Q49. Which digestive enzyme works immediately downstream of gastric pepsin in protein digestion?

• Pancreatic trypsin in the small intestine
• Lipase in the stomach
• Amylase in the stomach
• Lysozyme in saliva

Correct Answer: Pancreatic trypsin in the small intestine

Q50. Which research observation would most strongly indicate that pepsin is an aspartic protease?

• Its activity is enhanced by EDTA
• Its active site contains two essential aspartate residues and is inhibited by pepstatin
• It requires a serine hydroxyl for catalysis and is inhibited by PMSF
• It is activated by divalent metal ions like Zn2+

Correct Answer: Its active site contains two essential aspartate residues and is inhibited by pepstatin

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com