Lipids (Fats)

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Lipids saturated. These are usually solid at room - Waxy cuticle on leaves.
temperature and are called fats. - Waxy layer on exoskeleton on insects.
Lipids are made up of the elements carbon, - Reduces water loss.
hydrogen and oxygen but in different If one or more bonds between the carbon atoms - Insoluble in water.
proportions to carbohydrates. The most common are double bonds, the lipid is unsaturated. - Similar to lipids but contain alcohol.
type of lipid is the triglyceride. These are usually liquid at room temperature and
are called oils.
Lipids can exist as fats, oils and waxes. Fats
and oils are very similar in structure Functions of Lipids Summery:
Storage - lipids are non-polar and so are Molecule Building Blocks Type of Bond
At room temperature, fats are solids and oils are insoluble in water and release more energy
liquids. Fats are of animal origin, while oils tend per gram than carbohydrates. Carbohydrate monosaccharide Glycosidic
to be found in plants. High-energy store - they have a high proportion bond
of H atoms relative to O atoms and so yield
Lipids Glycerol and Ester bond
more energy than the same mass of
Waxes have a different structure (esters of fatty fatty acids
acids with long chain alcohols) and can be found Proteins Amino-acids Peptide bond
Production of metabolic water - some water is
in both animals and plants.
produced as a final result of respiration.
Thermal insulation - fat conducts heat very
Triglycerides: slowly so having a layer under the skin
keeps metabolic heat in.
These are made up of 3 fatty acid chains Electrical insulation - the myelin sheath around
attached to a glycerol molecule. axons prevents ion leakage.
Waterproofing - waxy cuticles are useful, for
Fatty acids are chains of carbon atoms; example, to prevent excess evaporation
the terminal one having an OOH group from the surface of a leaf.
attached making a carboxylic group Hormone production - steroid hormones.
(COOH). The length of the chain is usually Oestrogen requires lipids for its formation,
between 14 and 22 carbons long (most as do other substances such as plant
commonly 16-18). growth hormones.
Buoyancy - as lipids float on water, they can
Three of these chains become attached to have a role in maintaining buoyancy in
a glycerol molecule which has 3 OH groups organisms.
attached to its 3 carbons. This is called a
condensation reaction because 3 water Phospholipids
molecules are formed from 3 OH groups
from the fatty acids chains and 3 H atoms
A phosphate-base group replaces one fatty acid
from the glycerol. The bond between the
chain. It makes this part of the molecule (the
fatty acid chain and the glycerol is called
head) soluble in water whilst the fatty acid chains
an ester linkage.
remain insoluble in water.
The 3 fatty acids may be identical or they may Due to this arrangement, phospholipids form
have different structures. bilayers (the main component of cell and
organelle membranes).
In the fatty acid chains the carbon atoms may
have single bonds between them making the lipid


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