Cell membrane

Introduction

Cell membranes are complex structures that surround the cell and perform a surprising number of tasks vital for cell function and survival. They are made up of lipids, proteins and carbohydrates.

• Lipids are primarily phospholipids, oriented such that their hydrophilic heads face intra- and extracellular fluids, and their hydrophobic tails face each other in the inner region of the cell membrane. This bilayer creates a selectively permeable barrier allowing some molecules to pass through easily (gases, water and steroid hormones), while blocking others (ions and large molecules). Cholesterol, another lipid in the cell membrane, regulates the flexibility and fluidity of the cell membrane.
• Proteins include integral and peripheral proteins. They support a variety of functions, including the transport of substances across the membrane, the initiation of intracellular reactions in response to chemical stimuli, the catalysis of metabolic reactions, the maintenance of the cell structure and the linkage of adjacent cells.
  
• Carbohydrates protrude from the cell membrane, forming a coating known as the glycocalyx. This structure is important for cell recognition and immune responses.

Explore concepts

The cell membrane

The cell membrane (or plasma membrane) surrounds the cell, enclosing the cytosol.

Structure of the cell membrane

Cell membranes are made up of a lipid bilayer dotted with proteins, and a smaller proportion of carbohydrates that protrude outwards.

Selective permeability of the cell membrane

The phospholipid bilayer makes the cell membrane selectively permeable; some molecules can cross it freely, while others are blocked.

Functions of the cell membrane

The elements of the cell membrane contribute to distinct functions.

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Summary