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Biological molecules(section 1) (saccharides (disaccharides (examples…
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Lipids
Shared characteristics
contain carbon, hydrogen and oxygen
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Roles of lipids
cell membranes(cell-surface membranes and membranes around organelles).
phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them.
Source of energy: when oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water
waterproofing: lipids = insoluble in water and therefore useful as a waterproofing. both plants and insects have waxy, lipid cuticles that conserve water, while mammals produce and oily secretion from the sebaceous glands in the skin
insulation: fats are slow conductors of heat and when stored beneath the body also help to retain body heat.
they also act as electrical insulators in the myelin sheath and around nerve cells.
protection: fat is often stored around delicate organs, such as the kidney
Phospholipids
similar to lipids except one of the fatty acid molecules = replaced by phosphate molecule. whereas fatty acid molecules repel water( are hydrophobic), phosphate molecules attract water(are hydrophilic).
Hydrophilic "head" , interacts with water (attracted to it) but not with fat.
Hydrophobic "tail" orients itself away from water but mixes readily with fat.
Molecules that have 2 ends(poles) that behave differently in this way are said to be polar.
means that when polar phospholipid molecules are placed in water they position themselves so that the hydrophilic heads are as close to the water as possible and the hydrophobic tails are as far away from the water as possible.
The structure of phospholipids related to their properties:
phospholipid molecules for a bilayer within cell-surface membranes. as a result, a hydrophobic barrier is formed between the inside and outside of a cell.
The hydrophilic phosphate "heads" of phospholipid molecules help to hold at the surface of the cell-surface membrane.
the phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane. These glycolipids are important in cell recognition.
Triglycerides
so called because they have 3 fatty acids (tri), combined with glycerol(glyceride).
each fatty acid forms an ester bond with glycerol in a condensation reaction. Hydrolysis of a triglyceride therefore produces glycerol and 3 fatty acids
as Glycerol molecule in all triglycerides = same, the differences o the properties of different fats and oils come from variations in the fatty acid groups.
there are over 70 different fatty acids and all have a carboxyl(-COOH) group with a hydrocarbon chain attached.
if chain has no carbon-carbon double bonds, the fatty acid = saturated bcs all the carbon atoms are linked to the maximum possible number of hydrogen atoms --> they are saturated with hydrogen atoms.
if there is a single double bond, it is mono-unsaturated, if more than one is present = polyunsaturated.
Structure of triglycerides related to their properties:
have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms and therefore are an excellent source of energy.
They have low mass to energy ratio, making them good storage molecules because much energy can be stored in a small volume. very beneficial to animals as reduces mass they have to carry.
Being large, non-polar molecules, triglycerides are insoluble in water. As a result their storage does not affect osmosis in cells or the water potential of them.
as they have a high ratio of hydrogen to oxygen atoms, they release water when oxidised and therefore provide and important source of water, especially for organisms living in dry deserts.
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