Cell Membrane Overview and Composition

Study Notes

The cell membrane is also known as the plasma membrane.
It's a gatekeeper, separating the cell's interior from the external environment.
It controls the movement of materials into and out of the cell.
The membrane is semi-permeable, allowing only some substances to pass through.

The cell membrane is composed of a phospholipid bilayer.
Phospholipids have hydrophilic heads and hydrophobic tails.
Hydrophilic heads are attracted to water, while hydrophobic tails repel water.
The bilayer structure arranges the tails inwards, away from the water inside and outside the cell.
Only small, fat-soluble molecules can pass directly through the phospholipid bilayer.

Proteins act like doorways within the membrane.
They allow larger or polar molecules to pass through, which cannot pass through the phospholipid bilayer independently.
Membrane proteins can be either integral or peripheral.
Integral proteins are embedded within the phospholipid bilayer and frequently span the entire membrane. They assist in transporting large and polar molecules.
Peripheral proteins are located on the surface of the bilayer. They can assist in cell signaling, acting as enzymes, or influencing shape and structure.
Integral proteins come in two types: Carrier and Channel
- Channel proteins are essentially open tubes that create pathways allowing molecules to pass through passively.
- Carrier proteins "pick up" molecules and carry them across the membrane—this process often requires energy (active transport).

The cell membrane is fluid because of its components (like lipids and proteins) that can move laterally within the membrane.
The membrane's dynamic behavior is likened to a mosaic, composed of various parts.