Cell Membranes
- Created by: sophieamyx
- Created on: 27-06-17 11:22
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- Cell membranes
- Small molecules such as oxygen and carbon dioxide can cross the membrane by diffusion
- Has a 'Fluid Mosaic' structure
- Made mainly of lipids, proteins and carbohydrates
- 1972, Fluid Mosaic model was said to be an arrangement of molecules in the membrane
- Phospholipid molecules form a bilayer
- This bilayer is 'fluid' as the phospholipids are constantly moving and proteins can move around within it
- The molecules have a head and tail
- Head is hydrophilic, loves water, heads face out towards water
- Tail is made of two fatty acids, hydrophobic and hates water, tail are on the inside, centre of the bilayer is hydrophobic
- Ions and other water-soluble substances cant pass through
- Molecules automatically arrange into the bilayer
- Protein molecules are scattered through the bilayer, like tiles in a mosaic
- Some proteins have a polysaccharide (a carbohydrate) chain attached - called glycoproteins
- Lipids also have a polysaccharide chain attached - called glycolypids
- Cholesterol is present in the membrane, fitting between the phospholipids, forming bonds and making them rigid
- Scientific evidence
- Before the 1970s, scientists believed cell membranes were made of a phospholipid layer between two continuous layers of protein
- This was due to Electron microscopes showed three layers
- EM techniques improved over time and showed a bi layer of phospholipids, new methods showed randomly distributed proteins
- Before the 1970s, scientists believed cell membranes were made of a phospholipid layer between two continuous layers of protein
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