Final answer:
Human plasma membranes principally consist of phospholipids and cholesterol, which together with proteins and carbohydrates, form the structural and functional components of the membrane.
Step-by-step explanation:
In human plasma membranes, you will find a variety of lipids that are crucial for its structure and function. The most prominent lipids are phospholipids and cholesterol. Phospholipids are composed of a glycerol backbone, two fatty acids, and a modified phosphate group, forming the primary structure of the membrane. Cholesterol is a lipid molecule made up of four fused carbon rings and is embedded within the phospholipid bilayer, contributing to the fluidity and stability of the membrane.
Other than phospholipids and cholesterol, the plasma membrane also contains various proteins and carbohydrates; proteins comprise approximately 50 percent of the membrane composition by mass, followed by lipids at 40 percent, and carbohydrates making up the remaining 10 percent. The specific proportions can vary depending on cell type and function, as seen in specialized cells like myelin and red blood cells. Carbohydrates are found on the exterior surface of the membrane attached to lipids and proteins, forming glycolipids and glycoproteins, respectively.