Which of the following is a type of protein found in the cell membrane?

• A. Actin filaments
• B. Transmembrane proteins
• C. Collagen fibers
• D. Myosin

Answer: (B)

Proteins that reside in the cell membrane and actually span the lipid bilayer are transmembrane proteins. They thread through the membrane, with hydrophobic regions that interact with the fatty acid core and hydrophilic parts that face the interior and exterior of the cell. This positioning lets them perform key membrane roles such as forming channels, acting as transporters, serving as receptors, or anchoring the membrane to the cytoskeleton.

Actin filaments are part of the cytoskeleton inside the cell and help with shape and movement. Collagen fibers are extracellular matrix proteins outside the cell that provide structural support. Myosin is a motor protein that interacts with actin to generate force, typically not embedded across the membrane. Explaining the organization helps connect why transmembrane proteins are the ones found spanning the membrane.