Cell surface membrane

Cell surface membrane

Controls the movement of substances into and out of the cell

Most molecules dont freely diffuse across it because many are

Not soluble in lipids and therefore cannot pass through phospholipid layer

Too large to pass through the channels in the membrane 

Of the same charge as the charge on the protein channels and so are repelled 

Electrically charged (polar) and therefore have difficulty passing through the non polar hydrophobic tails in the phospholipid bilayer 

Arrangement is known as fluid mosaic model. Fluid because

Individual phospholipid molecules can move relative to one another

This gives the membrane a flexible structure that is constantly changing in shape 

Arrangement is known as fluid mosaic model. Mosaic because 

Proteins that are embedded in the phospholipid bilayer vary in shape size and pattern in the same way as tiles in the mosaic 

Fluid mosaic structure

Phospholipids

Proteins

Carbohydrates

Animals cells contain cholesterol 

Links fatty acid chains together 

Stables and strengthens

Glycolipid

Act as a recognition site

Example for toxins 

Peripheral protein on inner surface 

Can also be enzymes catalysing reactions

Can move but never swap sides 

Help give the structure of the membrane 

Attached to the cytoskeleton 

Peripheral proteins on outer surface

Can also be enzymes

Act like receptors have a binding site like enzymes and can bind with things like hormones 

Can trigger reactions to take place 

Involved in cell signalling and recognition

Carbohydrate attached to

Glycoproteins

Cell coat

Glycocalyx

Involved in protection and cell recognition

Integral protein forming a channel

Involved in transport of substances across the membrane