Which enzyme is responsible for breaking down proteins?

The selected answer, Trypsinogen, is indeed related to the process of protein breakdown, but it's important to clarify its role in that specific context. Trypsinogen is actually an inactive precursor, or zymogen, of the enzyme trypsin, which is crucial for the digestion of proteins in the small intestine. Once activated, trypsin functions to cleave peptide bonds, facilitating the breakdown of proteins into smaller peptides and amino acids that can be easily absorbed by the body.

Trypsinogen is secreted by the pancreas and is converted to trypsin through the action of another enzyme called enterokinase. Therefore, while trypsinogen itself does not actively break down proteins, it is a vital component of the protein digestion pathway.

Other enzymes listed, such as amylase and lipase, are responsible for the breakdown of carbohydrates and fats, respectively, and cellulase is involved in digesting cellulose, a type of carbohydrate found in plant cell walls. Understanding the specific functions of these enzymes highlights why trypsinogen is a key player in protein digestion, provided that the focus is on its activation and subsequent role as trypsin.