What are cell membranes and how are they constructed? What do the pieces of a cell membrane do? This lesson will answer these questions by investigating major membrane components.

What Are Cell Membranes?

Let’s begin this lesson with a question: what do all cells have in common? Truth be told, there are several characteristics cells all share, things like basic metabolism or having genetic material. But for the purposes of this lesson, we’ll focus on the fact that all cells contain a cell membrane.

The cell membrane is the outer covering of a cell, and it’s responsible for controlling entry and exit of material from the cell. Cell membranes, regardless of whether they exist in plants, animals, fungi or bacteria, are all made of the same basic components. These components are phospholipids, proteins, carbohydrates and cholesterol.

Phospholipids

The first major component of the cell membrane is the phospholipid. Phospholipids are fats that form the majority of the membrane. In the cell membrane below, the red pieces with the two yellow tails are phospholipids.

Phospholipids are the red pieces with two yellow tails.
diagram of cell membrane

They are arranged in a double layer so that the tails face inward. This arrangement works because the head of the phospholipid is hydrophilic and immerses itself inside the watery environment inside and outside the cell. The fatty acid tails are hydrophobic and are repelled by water. By sandwiching the fatty acid tails within the membrane, it keeps them away from water while simultaneously immersing the heads in water.

Proteins

Proteins form another integral part of the cell membrane. Proteins are large molecules formed from long chains of amino acids. You’ll notice that there are many different types of proteins. These proteins perform functions such as moving materials across the membrane. For example, have you ever heard that eating bananas will help protect you from getting cramps? That’s because bananas contain potassium. This potassium is moved into your cells by proteins embedded in the cell membrane.

Carbohydrates

The third major component of cell membranes is carbohydrates. Carbohydrates are other large molecules that are made from simple sugars. These molecules generally hold cells together or act as sites where chemical-signaling molecules, such as hormones, can attach to the cell.

Cholesterol

Finally, we come to cholesterol. Cholesterol is a waxy, fat-like material found in all cell membranes. While cholesterol may sometimes be portrayed negatively in the media, it’s actually vital to our cells. Cholesterol’s function is to slightly immobilize the outside of the cell membrane. If cells lacked cholesterol, the membrane would be too fluid and not firm enough to maintain its functionality.

Lesson Summary

All living things are made of cells, and all those cells are contained in cell membranes. Membranes are responsible for controlling entry to and exit from cells. Cell membranes are made of four major components. Phospholipids are fats that create the vast majority of the surface of membranes. Interwoven into this surface are also proteins. Proteins are made of amino acid chains and function as transport devices within cells. Sometimes these proteins have carbohydrates extending from them. Carbohydrates are large molecules made from simple sugars. Their function is to link cells together or act as binding sites. Finally, the cell membrane has a slightly rigid nature that is created due to cholesterol. Cholesterol is a waxy material found embedded within the membrane.

Learning Outcomes

Your understanding of the major structural components of the cell membrane could enable you to accomplish these objectives:

  • Discuss the function and structure of cell membranes
  • Enumerate the four main components of cell membranes