Optometry Admission Test (OAT) Practice

What type of molecule is embedded in the phospholipid bilayer alongside cholesterol?

1. Carbohydrates

2. Proteins

3. Nucleic acids

4. Integrins

The correct answer is: Proteins

The correct answer identifies proteins as the types of molecules embedded within the phospholipid bilayer alongside cholesterol. This arrangement is crucial for the structure and functionality of cellular membranes. Proteins serve various roles, including facilitating transport across the membrane, acting as enzymes, and functioning as receptors for signaling molecules. They integrate into the bilayer due to their amphipathic nature—having hydrophobic and hydrophilic regions that interact appropriately with both the lipid layers and the aqueous environment surrounding the cell. Cholesterol also plays a significant role by stabilizing cell membranes and maintaining fluidity, particularly in varying temperature conditions. The presence of proteins within the bilayer not only complements the structural integrity provided by cholesterol but also adds to the dynamic nature of the membrane, allowing for communication and transport functions critical for cell viability. In contrast, while carbohydrates can be found associated with cell membranes, they primarily exist as glycoproteins or glycolipids, often on the extracellular surface rather than embedded within the bilayer itself. Nucleic acids are not part of the membrane structure; instead, they are generally confined to the cell nucleus or cytoplasm. Integrins, specifically, are a type of protein that serves as cell adhesion molecules, but they are not