a full summary of everything you need to know for aqa a level biology unit 1 - lipids. These notes have been created using a variety of class notes, textbooks, youtube videos and most importantly exact phrases from the AQA specification and previous mark schemes, condensed into the most important b...
lipids
L ipids are long hydrocarbon chains composed of hydrogen, oxygen and carbon. Fats are solid at room temperature,
whereas oils are liquid. They can be divided into two categories, triglycerides and phospholipids, but all lipids have
similar properties:
1. They contain carbon, hydrogen and oxygen
2. The proportion of oxygen and carbon and hydrogen is smaller than in carbohydrates, so they store more
energy than other molecules such as carbohydrates
3. They are insoluble in water and only soluble in organic solvents eg acetone and alcohol
These physical properties mean they have a wide range of uses and are well suited for their function:
1. A source of energy - when hydrolysis occurs, a large amount of energy is released in comparison to
carbohydrates and other molecules, making them an efficient energy store
2. Waterproofing - they are insoluble and water making them useful in plants for waxy cuticles and in animals
for sebaceous secretions in the skin
3. Thermal and electrical insulators - fats are poor conductors of heat, meaning they help to maintain and buffer
change in body temperature, as well as acting as an electrical insulator surrounding the myelin sheath in
nerve cells
4. Protection - fats are often found surrounding vital organs eg the heart
A lthough triglycerides and phospholipids do have different
structures, both contain fatty acids. Fatty acids arecarboxylic
acids made up of a hydrocarbon chain and a final hydroxyl group.
There are three main types of fatty acids, saturated,
monounsaturated and polyunsaturated.
S aturated fatty acids are where there are no double bonds between carbon
chains. This is because all of the carbon atoms are bonded to the maximum
amount of hydrogen atoms, so they are saturated with hydrogen atoms.
M onounsaturated fatty acids is where the fatty acid has a carbon chain with a
single double bond between carbon atoms.
P olyunsaturated fatty acids is where the fatty acid has a carbon chain with many
double bonds between carbon atoms.
Sometimes, the hydrocarbon chain is shortened to an R group so is R-COOH.
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