Cell Membrane Structure and Function

Study Notes

Structure and Composition

The cell membrane, also known as the plasma membrane, is a thin layer of lipid and protein molecules that surrounds the cell.
It is semi-permeable, allowing certain substances to pass through while keeping others out.
The cell membrane is composed of:
- Phospholipid bilayer: a double layer of phospholipid molecules with hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails.
- Proteins: embedded or attached to the phospholipid bilayer, performing various functions such as transport, signaling, and cell adhesion.

Functions

Regulation of what enters and leaves the cell: the cell membrane controls the movement of substances into and out of the cell through various transport mechanisms.
Protection: the cell membrane acts as a barrier, protecting the cell from its environment and maintaining internal conditions.
Cell signaling: the cell membrane plays a role in signal transduction, allowing cells to communicate with each other.
Cell adhesion: the cell membrane helps cells stick together and maintain tissue structure.

Transport Mechanisms

Passive transport: movement of substances down their concentration gradient, requiring no energy input from the cell.
- Diffusion: random movement of particles from high to low concentration.
- Osmosis: movement of water molecules from high to low concentration.
Active transport: movement of substances against their concentration gradient, requiring energy input from the cell.
- Carrier proteins: transport molecules across the cell membrane using energy from ATP.

Fluidity and Movement

Fluid mosaic model: the cell membrane is a dynamic, fluid structure with proteins and lipids moving laterally.
Lateral movement: proteins and lipids can move freely within the phospholipid bilayer.
Flip-flop movement: phospholipid molecules can rotate from one side of the bilayer to the other.

Importance

The cell membrane is essential for maintaining cellular homeostasis and regulating cellular activities.
Its dysfunction can lead to various diseases and disorders, such as cancer and neurological disorders.

Description

Understand the composition and functions of the cell membrane, including its role in regulating what enters and leaves the cell, protection, cell signaling, and cell adhesion. Learn about passive and active transport mechanisms and the fluid mosaic model.