Lipids, Cell surface membrane, etc.

Lipids:
Triglycerides are formed by a condensation reaction. Each fatty acid forms a bond with glycerol, and a water molecule in taken away on each, (Condensation reaction.) Hydrolysing a triglyceride is therefore, going to form glycerol and three fatty acids.
Fatty acids can vary by how saturated they are. If there are no double bonds it’s described as saturated as all of the carbons are linked to the maximum possible number of hydrogen atoms. If there is a single double bond it is mono-unsaturated, and if there is more then one double bond it is poly-unsaturated.
The structure of phospholipids is similar to lipids, except one fatty acid is replaced by a phosphate molecule. The fatty acids repel water (hydrophobic) but the phosphate molecules attract water (hydrophilic). Therefore, the phospholipids are made up of a hydrophilic head and a hydrophobic tail. This makes them polar, which means the have two ends that behave differently. In water, the hydrophilic end gets as close to the water as possible and attracts it, and the hydrophobic end goes as far from it as possible.
A presence of lipids is identified by the lipid emulsion test, and this is carried out by putting 2cm3 of the sample in a test tube with 5cm3 of ethanol, and shaking, to dissolve any lipid in the sample. You then add water and shake, and if a cloudy white emulsion is formed, then a lipid is present.
1) Fats and oils make up a group of lipids called triglycerides which, when hydrolysed, form glycerol and fatty acids. A fatty acid with more then one carbon –carbon double bond is called poly-unsaturated. In a phospholipid, the number of fatty acids is two, and these are described as hydrophobic because they repel water.
2) State two differences between a triglyceride and a phospholipid: a triglyceride has three fatty acids, whereas a phospholipid has two. The phospholipid is polar, and contains a phosphate molecule, whereas the triglyceride is not, and does not do either.
3) Because when oxidised, lipids produce almost twice the amount of energy the same amount of carbohydrate would, and if something is moving, it needs more energy released, so lipids are more efficient.

The Cell Surface Membrane:
The structure of the cell surface membrane is a bi-layer of phospholipids. One layer has all the hydrophilic heads pointing inwards, the other has them pointing outwards. The hydrophobic tails point inwards on both, protected from the water on both sides. It also contains proteins, intrinsic and extrinsic.
The function of the phospholipids in the membrane are to are to allow lipid soluble substances access to the cell, and to prevent water soluble molecules from having access. It also makes it flexible.
The proteins are there it add strength to the cell, and to act as carriers for water soluble molecules across the membrane. They form ion channels so active transport for sodium/potassium, etc, can take place. They form recognition sites by identifying cells, and act as receptors, for example, for hormones.
The fluid mosaic model is the way of explaining how all of the components of a membrane come together. It is fluid, because the individual phospholipid molecules can move, relative to each other. This makes the membrane flexible and constantly changing in shape. It is mosaic, because the proteins embedded in the bi-layer can vary in size and shape, much like the stones in a mosaic.

1) The overall function of cell surface membrane is to control the movement of substances and the conditions in and out of a cell.
2) The hydrophobic end of the phospholipid molecule towards the inside of the cell surface membrane.
3) A molecule that is soluble in lipids is likely to pass the phospholipids to get in and out of the cell. A mineral ion is water soluble, so it is likely to enter and exit the cell via an intrinsic protein (carrier).
4) It should be small and lipids soluble if a drug water to get through a cell surface membrane quickly.