4.1 Structure Of The Cell Surface Membrane

Introduction

• All membranes around and within cells have the same basic structure and are known as plasma membranes, and the membrane on plasma cells is known as the cell surface membrane (CSM)

• The CSM forms a boundary between the environment and the cytoplasm of the cell, allowing or different conditions to be established inside and outside of the cell.

• CSM controls substances moving in and out of the cell

Phospholipids

• Form a bilayer

• Hydrophilic heads face the outside of the CSM attracted by water on both sides

• Hydrophobic tails face the centre of the membrane of the CSM repelled by water

• Allow small, non polar, lipid soluble molecules to pass through the membrane via the phospholipid portion

• Prevent water soluble molecules from entering/leaving the cell

• Make membrane flexible and self-sealing

Proteins

• Spread throughout the CSM and can be embedded in the membrane 2 main ways

• 1 - embeded the bilayer and never extend completely across it to act as support or (in conjunction with glycolipids) as cell receptors to detect molecules such as hormones

• 2 - completely spanning from one side of the bilayer to the other as: