Functions of the cell membrane components

• backbone of the cell-surface membrane
• gives membrane much of its selectively or differentially permeable properties

• Increases membrane stability (temperature stability buffer)
• At high temperatures, it restricts the sideways movement of phospholipid molecules and decreases membrane fluidity
• At low temperatures, the cholesterol helps to maintain membrane fluidity by acting as a wedge between adjacent phospholipid molecules and preventing them from sticking together

Makes membrane less fluid at high temperatures and more fluid at low temperatures

• provide stability and support as they help to 'anchor' phospholipid molecules
• act as enzymes:

-ideal place for enzymes in terms of substrate availability and pH

-need replaced less than other enzymes

• act as adhesion sites - areas where adjacent cells are held together
• involved in cell recognition and receptors or antigens
• transport of substances across the bilayer

Channel Proteins

• span the membrane
• create a hydrophilic channel that allows polar molecules to bypass the hydrophobic centre of the bilayer
• may be permanently open or controlled opening (gated)

Carrier Proteins

• carry specific ions and molecules across the membrane
• the molecules may have charged groups or the molecules/ions have to be moved against the concentration gradient
• can change shape to carry the substance from one side of membrane to the other

The glycocalyx layer is the layer on the outside of the cell-surface membrane of polysaccharides that bind to the protein or lipid (glycoproteins or glycolipids)

• They are involved in cell-to-cell recognition, allowing cells of similar type to recognise each other and group together to form tissues
• Some glycoproteins act as antigens and receptor sites - provide sites on the cell-surface membrane that particular molecules fit (can occur because the receptor site and specific molecule concerned are complementary in shape to each other)
• Receptor sites are important in hormone action and in the passage of neurotransmitters between neurones
• Glycoproteins/lipids can form hydrogen bonds with water molecules outside the membrane so can help stabilise the membrane