Transform Lengthy Notes Into Concise Summaries

The cell membrane, also called the plasma membrane, is a thin, flexible barrier that surrounds all cells. It regulates what enters and leaves the cell and maintains the cell's electric potential. The cell membrane is composed primarily of a phospholipid bilayer, which consists of two layers of phospholipids with their hydrophilic (water-loving) heads facing outward and their hydrophobic (water-fearing) tails facing inward toward each other.

Embedded within this bilayer are various proteins that serve different functions. Integral proteins span the entire membrane and often function as channels or transporters, allowing specific molecules to enter or exit the cell. Peripheral proteins are attached to the inner or outer surface of the membrane and may serve as enzymes or structural components.

The cell membrane also contains cholesterol, which helps maintain membrane fluidity and stability. Additionally, glycoproteins and glycolipids on the outer surface of the membrane serve as recognition sites for other cells and molecules.

The fluid mosaic model describes the cell membrane as a fluid structure with various proteins embedded within it, capable of lateral movement. This fluidity is essential for many cellular processes, including cell growth, division, and the formation of intercellular junctions.

Transport across the cell membrane occurs through several mechanisms. Passive transport, including simple diffusion and facilitated diffusion, does not require energy and moves molecules from areas of higher concentration to areas of lower concentration. Active transport, on the other hand, requires energy (usually in the form of ATP) and can move molecules against their concentration gradient.