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Biological Environment > Cell Membrane |
This site tells the story of the history of the universe. Click Earlier and Later to follow the story. Note: Many facts have been simplified to make them easier to understand. |
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Soon after life began there evolved a thin oily skin around a group of living molecules. This skin is called the cell membrane. It is not clear how or why the membrane was first formed, but it was a great step forward for life. It kept life's molecules together and also protected them from harmful chemicals which could not pass through the membrane.
A membrane consists of molecules which are sticky (they stick to water) at one end and slippery (they do not stick to water) at the other. When placed in water, these molecules line up with their sticky heads facing outwards and their slippery tails inwards. So a membrane has two layers, as shown in the diagram.
To find out why water molecules are sticky, see the Hydrogen Bond page.
As life developed, new proteins evolved which could use the special properties of the membrane. If a protein had sticky amino acids at one end and slippery ones at the other, it could float in the membrane with the sticky half in the watery cell and the slippery half in the membrane. It could then do special jobs, such as detecting food molecules in the outside world. |
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Biological Environment > Cell Membrane |
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Basic Information |
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