Cell Membranes & Transport: Structure and Function

Cell Membranes

Overview of Cell Membranes

The cell membrane (also called the plasma membrane) is a fundamental structure in all living cells. It separates the interior of the cell from the external environment and plays a critical role in maintaining cellular integrity and function.

• Selective Permeability: The membrane controls the movement of substances in and out of the cell, allowing only certain molecules to pass.

• Cell Communication: Membranes contain proteins and other molecules that facilitate communication between cells and their environment.

• Cell Shape and Attachment: The membrane helps maintain cell shape and enables cell-to-cell attachment and signaling.

Phospholipid Structure

The primary component of cell membranes is the phospholipid. Phospholipids are amphipathic molecules, meaning they have both hydrophilic and hydrophobic regions.

• Hydrophilic Head: The phosphate-containing head is attracted to water.

• Hydrophobic Tail: The fatty acid tails repel water.

• Phospholipids arrange themselves into a bilayer, with heads facing outward toward water and tails facing inward, away from water.

Saturated vs. Unsaturated Fatty Acids

Phospholipid tails can be either saturated or unsaturated, affecting membrane fluidity.

• Saturated Fatty Acids: Have straight tails, allowing them to pack tightly together, making the membrane less fluid.

• Unsaturated Fatty Acids: Have kinked tails due to double bonds, preventing tight packing and increasing membrane fluidity.

• Example: Membranes with more unsaturated fatty acids are more flexible and less rigid.

Type of Fatty Acid	Structure	Effect on Membrane
Saturated	Straight tails	Packs tightly, less fluid
Unsaturated	Kinked tails	Packs loosely, more fluid

Additional info:

• Cholesterol is another important component that modulates membrane fluidity, preventing it from becoming too rigid or too fluid.