Lipids are significant in the roles of fats and oils in living things. When triglycerides are oxidised in respiration, a lot of energy is released which is used to make ATP. This is useful as fats and oils release roughly twice as much energy in comparison to carbohydrates. Triglycerides have a high proportion of hydrogen atoms relative to oxygen atoms and therefore yield more energy compared to carbohydrates; this is the result of fats being reduced more than carbohydrates. As fats have a lower proportion of oxygen compared to carbohydrates more of the oxygen in respiration of fats comes from the atmosphere; equally in the oxidation of carbohydrates a greater proportion of oxygen is present in the molecule itself. Fat resultantly forms a concentrated, insoluble energy store; lipids are non-polar causing them to be insoluble in water.
Fat is significant for animals that endure long unfavourable seasons. This is due to fat conducting heat very slowly; consequently having a layer under the skin insulates metabolic heat in. Oils are a major energy store in seeds and industrially are extracted for human use.
The bonds between the fatty acid chains are what make them different. The three fatty acids could be identical or not, a fatty acid may have single bonds making it a saturated lipid. These are more commonly known as fats and are solid at room temperature.
Lipids can also occur as waxes or steroids depending on the structure of the lipid as well as the amount of fatty acids and glycerol’s. Triglycerides consist of 3 fatty acid chains and 1 glycerol molecule; this is the resultant of a condensation reaction. They appear to be macromolecules due to the hydrophobic behaviour resulting in the small molecules clumping together.
Lipids are also significant in electrical insulation within humans. The myelin sheath around the axons of neutrons act as electrical insulators to the cells’ plasma membrane ensuring the nerve impulse can pass down the axon.
Phospholipids are important within cells and have a similar structure to triglycerides. The difference being that one fatty acid group is replaced by a phosphate group. the phosphate group is ionised therefore has a negative charge this causes the phosphate group to be hydrophilic. The glycerol part of the substance is hydrophobic. This causes the lipids to align themselves when in water, with the hydrophilic end facing the water and the hydrophobic end moving as far away as possible from the water; this is significant in the structure of the cell membrane as it is because of these characteristics that the formation of bilayers exists. Bilayers are major components in the plasma membrane which surrounds all cell organelles.
Steroids are a much different and structurally differ as a form of lipid involving triglycerides. Steroids are arranged in a set of complex carbon rings and most of the molecule is hydrophobic, leaving the polar –OH group as hydrophilic. An important form in regards to humans of a steroid is cholesterol which is highly significant in life. Cholesterol is an important component of the cell membrane of plants and animals. Cholesterol is vital in the production of sex hormones progesterone, oestrogen and testosterone. Bile salts are also synthesised from cholesterol. Oestrogen requires lipids for its formation, as do other substances such as plant growth hormones. Cholesterol, however, as is widely known can be harmful in excess and can form atherosclerosis (a condition in which fatty material is deposited along the walls of arteries. This fatty material thickens, hardens, and may eventually block the arteries). Just as other lipids cholesterol is insoluble so is carried to sites where it is metabolised or stored via the blood plasma combined wit soluble proteins.
Waxes are, finally, the other form of lipids. They are esters formed from a fatty acid and a complex alcohol. These are produced by plants and help to limit water loss through evaporation, as form a waxy cuticle. Wax is secreted by insects for the same role on the outer surface of their cuticle. Bees use wax in the honeycomb cells they build for rearing their larvae and storing honey.
Conclusively lipids are highly significant in many life processes. The creation of lipids allows both plant and animal life to carry out vital functions in order to maintain life. Without lipids our bodies would be polluted from cells being invaded by substances that shouldn’t enter and thus is an extremely important component for the sustenance of life.
