Membranes at the cell surface (plasma membrane)
- Plasma membranes control which substances enter and leave the cell. They're partially permeable - they allow some molecules through but not others.
- Substances can move by diffusion, osmosis or active transport. They also allow recognition by other cells and cell communication.
Membranes within cells
- Membranes around organelles divide the cell into different compartments. This makes different functions more efficient. (Mitochondria - Respiration)
- The membranes of some organelles are folded, increasing their surface area and making chemical reactions more efficient (Mitochondria - Increased respiration)
- Membranes can form vesicles to transport substances between different areas of the cell. (Proteins - Protein Synthesis)
- Membranes within cells are also partially permeable. (RNA and DNA)
- Consist of phospholipids, proteins and carbohydrates.
- Fluid Mosaic Model : Phospholipid bilayer form a continuous, double layer.
- Fluid: because the phospholipids are constantly moving.
- Protein molecules are scattered through the bilayer like a mosaic.
- Glycoproteins: Protein with a polysaccharide (carbohydrate chain) attached.
- Glycolipids: Lipids with a polysaccharide chain attached.
- Cholesterol molecules are also present.
- Barrier to dissolved substances (Hydrophilic Head - Hydrophobic Tail)
- Arranged in a bilayer - heads face out to the water.
- The centre is hydrophobic so ions…