Biology 2e - Components and Structure of Plasma Membranes

Learning Objectives

• Understand the fluid mosaic model of cell membranes.
• Describe the functions of phospholipids, proteins, and carbohydrates in membranes.
• Discuss membrane fluidity.

Plasma Membrane Overview

• Defines the cell, outlines borders, and determines environmental interactions.
• Functions include selective permeability, flexibility for shape changes, and cell recognition.
• Integral proteins in the membrane transmit signals and interact with extracellular elements.

Fluid Mosaic Model

• Proposed by S.J. Singer and Garth L. Nicolson in 1972.
• Describes the membrane as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates.
• Plasma membranes are 5-10 nm thick, with components allowing fluidity.

Components of the Plasma Membrane

Phospholipids

• Amphiphilic molecules with hydrophilic heads and hydrophobic tails.
• Form lipid bilayers in aqueous environments, separating internal and external cell environments.

Proteins

• Integral proteins (integrins) span the membrane and facilitate signal transmission.
• Peripheral proteins attach to the exterior or interior surfaces for functionality or structural support.

Carbohydrates

• Present on the exterior surface as glycoproteins or glycolipids.
• Facilitate cell recognition, critical for immune response and tissue formation.

Membrane Fluidity

• Maintained by the mosaic nature and unsaturated fatty acid content.
• Cholesterol acts as a buffer to temperature changes, ensuring membrane fluidity.

Evolution Connection

• Glycoprotein and glycolipid patterns allow specific viral infections (e.g., HIV).
• Viruses bind to specific cell receptors, facilitating entry and immune response challenges.

Career Connection: Immunologist

• Focus on cell recognition sites is crucial for vaccine development.
• Immunologists study infectious diseases, immune disorders, and vaccine technology.
• Requires advanced degrees (PhD, MD) and specialized training.

Conclusion

The fluid mosaic model explains the dynamic and complex nature of the plasma membrane, highlighting how its components work together to fulfill essential cellular roles.