SANTR
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I would appreciate it if someone could explain what is mean by the phrase 'help to hold' in the context below?
The hydrophilic phosphate heads of phospholipid molecules, ‘help to hold’ at the surface of the cell surface membrane?
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Kallisto
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(Original post by SANTR)
I would appreciate it if someone could explain what is mean by the phrase 'help to hold' in the context below?
The hydrophilic phosphate heads of phospholipid molecules, ‘help to hold’ at the surface of the cell surface membrane?
Would say that means the hydrophilic phosphate heads hold the whole cell surface membrane together. Would make sense, as this surface consists of hydrophilic phosphate heads. Click here to see that.
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timthechemist
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Cell membrane is a bi-layer. The Hydrophillic head groups are a charged molecule which is therefore polar. They are actually fluid. Its a misconception people have that there is rigidity, they "self assemble" simply due to the nature of Hydrophobic tails wishing to escape water and congregate together. The reason is that water molecules of H20 do not like being ordered.

The reason all fats/oils will bunch together in water, is to minimise surface area that faces the water. With lower surface area, less H20 molecules around the fat/oil, need to be in an 'ordered' state (Look up Micelles and how soap works as a carrier, also look up Entropy and how water wants disorder). So molecules that are insoluble in water (In this case, the tails of phospholipids) want to escape water as well. Just with a membrane, it is facing water on both sides, so thats why it is a lipid -bilayer.

But when they say help to hold, it sounds stupid, because they are actually held by the forces I explained above. The orientation of the head groups faces water as a natural consequence of intermolecular forces (IMF) being the 1. chemistry of transient hydrogen bonds, and the 2. Trying to achieve the lowest state of energy with the situation of ordered H2O molecules.

As a matter of fact, look up the "Fluid Mosaic Model" and 2 dimensional model, the membrane is not rigid at all, those individual phospholipids are not even covalently bonded to each other. If there was any evidence of "structure" it would be more the extracellular sugar linkages and webbing matrix parts, but thats secondary to what I just explained.
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Kallisto
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(Original post by timthechemist)
Cell membrane is a bi-layer. The Hydrophillic head groups are a charged molecule which is therefore polar. They are actually fluid. Its a misconception people have that there is rigidity, they "self assemble" simply due to the nature of Hydrophobic tails wishing to escape water and congregate together. The reason is that water molecules of H20 do not like being ordered.

The reason all fats/oils will bunch together in water, is to minimise surface area that faces the water. With lower surface area, less H20 molecules around the fat/oil, need to be in an 'ordered' state (Look up Micelles and how soap works as a carrier, also look up Entropy and how water wants disorder). So molecules that are insoluble in water (In this case, the tails of phospholipids) want to escape water as well. Just with a membrane, it is facing water on both sides, so thats why it is a lipid -bilayer.

But when they say help to hold, it sounds stupid, because they are actually held by the forces I explained above. The orientation of the head groups faces water as a natural consequence of intermolecular forces (IMF) being the 1. chemistry of transient hydrogen bonds, and the 2. Trying to achieve the lowest state of energy with the situation of ordered H2O molecules.

As a matter of fact, look up the "Fluid Mosaic Model" and 2 dimensional model, the membrane is not rigid at all, those individual phospholipids are not even covalently bonded to each other. If there was any evidence of "structure" it would be more the extracellular sugar linkages and webbing matrix parts, but thats secondary to what I just explained.
Nice answer! I guess you have cleared the confusion all of us out. Would say so.
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