Which type of integral membrane proteins consist of multiple peptide chains?

The correct choice refers to the classification of integral membrane proteins, particularly those that are characterized by their structure and the number of peptide chains they contain.

Type 4 integral membrane proteins are indeed known to consist of multiple peptide chains. These proteins can form large complexes, often referred to as multimeric proteins, and they can span the membrane multiple times. The presence of multiple peptide chains allows for complex interactions and functionalities, which are vital in various biological processes.

In contrast, Type 1, Type 2, and Type 3 proteins are typically characterized as having single peptide chains that either pass through the membrane only once or have different orientations and anchoring mechanisms. Type 1 proteins usually have a signal peptide that directs them to the endoplasmic reticulum and possess a single membrane-spanning domain, Type 2 proteins also have a single membrane-spanning region but differ in their orientation, and Type 3 proteins consist of several transmembrane regions but do not imply the presence of multiple distinct peptide chains like those in Type 4.

Overall, the classification of integral membrane proteins is crucial for understanding their biological roles, structures, and how they interact within cellular membranes.