The Cell membrane surrounds all living cells and is the most important organelle, there is also a similar plasma membrane that surrounds all the organelles except for the ribosome.
The membrane controls how and what substances can move in and out of the cell/organelle
The structure of the membrane is often referred to as the “Fluid Mosaic Model”; this is because of the way it is structured
It is composed of phospholipids, proteins, and carbohydrates, which are arranged in a fluid mosaic structure.
The phospholipids are arranged in a “bilayer”. With their hydrophilic (water attracting) phosphate heads facing outwards and their hydrophobic (water fearing) tails facing in towards the middle of the bilayer.
The hydrophobic layer acts as a barrier to all but the smallest molecules and effectively isolating the two sides of the membranes.
Some membranes contain phospholipids with different fatty acids, which affect the strength and flexibility.
Animal cells also have cholesterol linking the fatty acids together and so stabilising and strengthening then membrane
The proteins usually span from one side of the bilayer to the other. These are called integral proteins.
But some sit on one side of the bilayer, these are called peripheral proteins.
Proteins comprise approximately 50% of the mass of the membrane.
The integral proteins (ones which span across the whole bilayer) are usually involved in the transporting of substances across the membrane.
The proteins that are on the inside of the bilayer are often attached to the cytoskeleton and are involved in maintaining the cell’s shape. They may also be enzymes for catalysing reactions.
The proteins on the outside act as receptors, with a specific binding site, where hormones or other chemicals can bind.
The Carbohydrates are found on the outer surface and are attached to the proteins or sometimes the phospholipids.
Proteins with a carbohydrate...
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