Correct option is D
Protein digestion involves a complex cascade of enzymatic breakdown of polypeptides into amino acids, occurring in multiple compartments of the gastrointestinal tract. Enzymes such as peptidases, carboxypeptidases, trypsin, chymotrypsin, and enterokinase play critical roles.
Let us analyze each statement individually:
Statement A: Chymotrypsin does not generate peptides with C-terminal neutral amino acids. Incorrect
- Chymotrypsin cleaves peptide bonds on the carboxyl side of aromatic and some neutral amino acids, such as phenylalanine, tyrosine, tryptophan, and sometimes leucine.
- Hence, chymotrypsin does produce peptides ending with neutral or aromatic amino acids.
Statement B: Trypsin generates peptides with C-terminal basic amino acids. Correct
- Trypsin cleaves peptide bonds after basic amino acids, mainly lysine and arginine, producing peptides with C-terminal basic residues.
Statement C: Carboxypeptidase B acts on aromatic amino acids. Incorrect
- Carboxypeptidase B specifically cleaves basic amino acids (arginine and lysine) from the C-terminal end.
- It does not act on aromatic amino acids. Carboxypeptidase A acts on aromatic and aliphatic amino acids.
Statement D: Carboxypeptidase A employs zinc ion for hydrolysis. Correct
- Carboxypeptidase A is a zinc metalloenzyme.
- The zinc ion in its active site helps in catalyzing peptide bond hydrolysis.
Statement E: The brush border enterokinase has no polysaccharides attached to it. Incorrect
- Enterokinase (also known as enteropeptidase) is a glycoprotein, meaning it has polysaccharide (carbohydrate) moieties attached to it.
Statement F: The final digestion to amino acids occurs in the intestinal lumen, the brush border, and the cytoplasm of the mucosal cells. Correct
- Protein digestion begins in the lumen (stomach and small intestine), continues via brush border peptidases, and cytoplasmic peptidases in mucosal cells complete the process.
