AQA A Level Biology复习笔记2.4.2 Components of Cell Surface Membranes
Phospholipids, Cholesterol, Glycolipids, Proteins & Glycoproteins
- The cell membranes of all organisms generally have a similar structure
- Cell membranes contain several different types of molecules:
- Three types of lipid:
- Phospholipids
- Cholesterol
- Glycolipids?(also containing carbohydrates)
- Two types of proteins:
- Glycoproteins?(also containing carbohydrates)
- Other proteins?(eg. transport proteins)
- Three types of lipid:
- Phospholipids:
- Form a?bilayer?(two layers of phospholipid molecules)
- Hydrophobic tails (fatty acid chains) point in towards the membrane interior
- Hydrophilic heads (phosphate groups) point out towards the membrane surface
- Individual phospholipid molecules can move around within their own monolayers by diffusion
- Cholesterol:
- Cholesterol molecules also have hydrophobic tails and hydrophilic heads
- Fit between phospholipid molecules?and orientated the same way (head out, tail in)
- Are absent in prokaryotes membranes
- Glycolipids:
- These are?lipids with carbohydrate chains?attached
- These carbohydrate chains project out into whatever fluid is surrounding the cell (they are found on the?outer phospholipid monolayer)
- Glycoproteins:
- These are?proteins with carbohydrate chains?attached
- These carbohydrate chains also project out into whatever fluid is surrounding the cell (they are found on the?outer phospholipid monolayer)
- Proteins:
- The proteins embedded within the membrane are known as?intrinsic proteins?(or?integral?proteins)
- They can be located in the?inner or outer phospholipid monolayer
- Most commonly, they span the entire membrane?– these are known as?transmembrane proteins
- Transport proteins?are an example of transmembrane proteins as they cross the whole membrane
- Proteins can also be found on the inner or outer surface of the membrane, these are known as?extrinsic proteins?(or?peripheral?proteins)
Exam Tip
Make sure you can?draw?and?label?all the above structures on a diagram of the fluid mosaic model of cell membranes.You can use an annotated diagram to state the?functions?of the above structures.?
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