Cell Membrane Structure Dr. V.P.C. Rajakaruna MBBS(COLOMBO)

Content Introduction to cell membrane Composition

What is cell membrane? Outer most covering of the cell Cell membrane separates living cell from nonliving surroundings Selectively permeable Consists of phospholipids and proteins mainly and other macromolecules such as cholesterol and carbohydrate

Fluid-mosaic model Phospholipid bilayer with embedded proteins, fluid consistency and a mosaic pattern of embedded proteins

Composition

Phospholipids Fatty acid tails hydrophobic Phosphate group head hydrophilic Arranged as a bilayer Phosphate Fatty acid

Hydrophilic (water-loving) polar heads of the molecules lie on the outward-facing and inward-facing surfaces of the membrane. Hydrophobic (water-fearing) nonpolar tails extend to the interior of the membrane.

Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

Other components

Proteins Peripheral proteins Integral proteins loosely bound to surface of membrane cell surface identity marker Integral proteins penetrate lipid bilayer, usually across whole membrane transmembrane protein transport proteins channels, permeases (pumps)

Many Functions of Membrane Proteins Outside Plasma membrane Inside Enzyme activity Cell surface receptor Transporter Cell surface identity marker Attachment to the cytoskeleton Cell adhesion

Carbohydrates Glycolipids - phospholipids with carbohydrate chains attached Glycoproteins -proteins have carbohydrate chains attached. The carbohydrate chains of glycolipids and glycoproteins form the glycocalyx

Functions of the Glycocalyx cell-to-cell recognition cell-cell adhesion reception of signal molecules. The diversity of carbohydrate chains is enormous, providing each individual with a unique cellular “fingerprint”.

Cholesterol Helps maintain the integrity of the cell membrane, and plays a role in facilitating cell signaling ( meaning the ability of your cells to communicate with each other), protecting the proteins and giving them a supportive cover.