3.1.3 Lipids Flashcards
What are lipids?
+ contain C,H,O
+ less oxygen in proportion when compared to carbs
+ insoluble in water
+ but are soluble in alcohol and acetone
+ natural fats and oils are compounds of glycerol and fatty acids
+ fats are solid at room temp and oils are liquids (because fatty acid molecules in oils are smaller than those in fats)
What is the role of lipids?
+ when oxidised provide x2 as much energy as carbs
+ plants and insects have waxy, lipid cuticle that conserve water
+ mammals secrete oily substances from sebaceous lands in the skin
+ insulation= slow conductors of heat so help bodies retain heat. Also used in electrical insulation (myelin sheath around nerve cells)
+ protection= stored around delicate organs like kidneys
What are triglycerides?
+ synthesis of 3 fatty acids and one glycerol
+ main groups of lipids are tryglycerides and phospholipids
+ involves a condensation reaction
+ each OH group in the glycerol molecule reacts w/ the COOH group of the fatty acid
+ one water molecule is removed and an oxygen bond (ester bond) is established between the fatty acid and glycerol
Function of triglycerides?
+ high C-H bonds ratio which are a good source of energy
+ low mass-energy ratio making them good storage molecules
+ large, non-polar molecules therefore insoluble in water (water potential not affected)
+ high ratio of H:O atoms
+ release water when hydrolysed providing source of water for desert animals
What is the emulsion test?
1.Take a completely dry and grease-free test tube (to ensure only the fat from the sample is being measured)
2. To 2cm^3 of crushed sample being tested add 5cm^3 of ethanol
3.Shake the tube thoroughly (to disperse/dissolve the sample)
4. Add 5cm^3 of water and shake gently
5. A cloudy white emulsion indicates the presence of a lipid (cloudy= droplets of fat, not a precipitate)
6. Repeat the procedures using water instead of the sample (to act as a control)
7. Light passing through this is refracted as it passes from oil droplets to water droplets making it appear cloudy
What is the structure of a phospholipid?
+ hydrophilic head attracts water (as it is charged)
+ due to the phosphate being charged it repels other fats
+ hydrophobic tail repels water but will mix with other fats
+ fatty acids are not charged
How is the structure of a phospholipid related to its function?
+ Have 2 charged regions so they are polar
+ in water they are positioned so that the heads are exposed to water and the tails are not
+ this phospholipid bilayer membrane structure which makes up the plasma membrane around cells
