2 4 membranes

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2.4 – Membranes 2.4.1 - Draw and label a diagram to show the structure of membranes

Phospholipid Bilayer - This is arranged with the hydrophilic phosphate heads facing outwards, and the hydrophobic fatty acid tails (consisting of hydrocarbon chains) facing into the middle of the bilayer. It is a barrier against all molecules except the smallest, COâ‚‚ and Oâ‚‚. The phospholipids can change position on the horizontal plane, but not the vertical. Integral Proteins - These usually span from one side of the phospholipid bilayer to the other. They are usually involved in transporting substances across the membrane. Peripheral Proteins - These sit on the surfaces. They will slide around the membrane quickly and collide with each other, but will never flip from one side to the other. The ones on the inside of the membrane are often involved in maintaining the cell's shape or motility. These might also be enzymes, catalysing reactions in the cytoplasm. Glycoproteins - These are usually involved in cell recognition which is part of the immune system. They can also act as receptors in cell signalling such as with hormones. Cholesterol - Binds together lipid in the plasma membrane reducing its fluidity as conferring structural stability. This is called the fluid mosaic model because it is in a fluid state, and in electron micrographs of the membrane, the proteins form a mosaic pattern.

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