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Chpt 4: Cell membrane and
transport
Describe the fluid mosaic model of membrane structure and phospholipids
The membrane structure is described as fluid since proteins and phospholipids
are able to move about by diffusion, and, when observed from the top, a
pattern is created by the scattered protein molecules
Phospholipids
Have a hydrophillic phosphate head, and hydrophobic fatty acid tails
When dissolved in water, phospholipids can form:
1. A single layer of molecules (monolayer)
2. A micelle
3. Phospholipid bilayer: With hydrophilic heads sticking out, and
hydrophobic tails pointing towards the centre = hydrophobic region is
created
4. Bilayers with a membrane-bound compartment
Describe the components of a cell surface membrane
1. Phospholipids
Non-polar fatty acid tails point inwards to create a hydrophobic region,
whilst the polar phosphate heads face outwards into the surrounding
aqueous medium
Contribute to the fluidity of membrane
2. Cholesterol
Chpt 4: Cell membrane and transport 1
, Have a 'raindrop' or 'tadpole shape' where the 'tail' points inwards into
the hydrophobic region
Align between phospholipid molecules
Also contribute to the fluidity of membrane
3. Glycolipids
Lipid molecules with carbohydrate chain attached to it:
Carb chain can act as a receptor
Carbohydrate chains project into the surrounding aqueous medium
Present on the extrinsic side
4. Glycoproteins
Proteins with carbohydrate chain attached to it
Carb chain can act as a receptor
Carbohydrate chains project into the surrounding aqueous medium
Present on the extrinsic side
5. Proteins
Types of proteins:
1. Transport proteins: channel and carrier
2. Peripheral proteins: only on one side (intrinsic or extrinsic)
3. Transmembrane proteins: span the entire width of membrane
Chpt 4: Cell membrane and transport 2
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