Cell membranes

a)   Outline the roles of membranes within cells and at the surface of cells;

• Separate the cell contents from the outside environment.

• Separate cell components from the outside environment.

• Hold the components of some metabolic pathways in place.

• Cell recognition and signalling

• Regulating the transport of materials into or out of the cells.

b)   State that plasma membranes are partially permeable barriers;

c)    Describe, with the aid of diagrams, the fluid mosaic model of membrane structure;

A bilayer of phospholipid molecules form the main structure. A variety of proteins are studded in the bilayer, some partially embedded (extrinsic) whereas some completely span the membrane (intrinsic)

d)   Describe the roles of the components of the cell membrane;

1. Phospholipids,

   Have a hydrophobic head and a fatty (hydrophilic) acid tail. These form a bilayer separating the cell from the outside. They are fluid, so that components can move around freely. They are also permeable to small and/or non-polar molecules, but impermeable to large molecules and ions.

   Cholesterol,

   Gives the membranes mechanical stability by sitting between fatty acid tails and therefore making the barrier more complete. Preventing molecules like water and ions from passing through the membrane.

   Glycolipids,

   Phospholipid molecules that have a carbohydrate part attached. They are used for cell signalling, cell surface antigens and cell adhesion.

   Proteins

   Channel proteins allow the movement of some substances, such as the large molecule sugar, into and out of the cell as they can’t travel directly through the cell surface membrane. Carrier proteins actively move substances across the cell membrane.

   Glycoproteins,

            Phospholipid molecules with a protein attached. Same function as glycolipids.

e)  …