Membranes

• They are involved in intracellular and intercellular transport
• Membranes allow the contents of eukaryotic cells to be divided into specialed compartments
• They are often the site of complex chemical rections

Proteins and phospholipids

A mosaic of proteins bobbing in a fluid bilayer of phospholipids

Phospholipids - they have hydrophillic and hydrophobic sections so the hydrophillic heads form a stable membrane structure in contact with aqueous solutions and the hydrophobic tails stay in the centre of the bilayer away from water

Van der waals forces

It alters the fluidity of the membrane by breaking up the van der waals forces and close packing of the phospholipid tails and prevents lipid crystalisation at low temperatures

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Integral proteins

Proteins that can be embedded in one side only or go across the membrane

Peripheral proteins

Glycoproteins

• They transport molecules across a membrane down a concentration gradient
• Channel proteins facilitate diffusion

They pump ions and molecules against a concentration gradient

The hydrolysis of ATP

They allow the location of catalysis to be controlled within a cell

They allow the cytoskeleton to adhere to the membrane for the structural support of the cell.  They are also used to attach to the extra cellular matrix to hold the cell in one place

They enable an organism to identify which cells are its own and which cell are not supposed to be present allowing an immune response

They react to the attachment of hydrophilic signalling molecules stimulating a response within the cell such as the phosphorylation of an enzyme which will then be activated

To increase the surface area for chemical reactions

• endoplasmic reticulum
• golgi apparatus
• vesicles
• vacuoles
• microbodies