3.1.3 Lipids Flashcards
what elements do lipids contain?
carbon, hydrogen, oxygen
what are triglycerides made from?
one molecule of glycerol + three molecules of fatty acids
how do triglycerides form?
formed by the condensation of one molecule of glycerol + 3 molecules of fatty acids
what bonds do triglycerides form?
ester bonds
where do triglycerides store energy in?
plants, animals and some bacteria
what are the tails made of on fatty acids?
hydrocarbons and one carboxylic acid
what does the tails being hydrophobic mean?
it repels water molecules which make lipids insoluble in water
what is a hydrocarbon chain also known as in a fatty acid?
R
how many different fatty acids are there?
70
what are saturated fatty acids?
don’t have double covalent bonds between their carbon atoms
- all carbons have full number of hydrogens possible
- higher melting point than unsaturated - solid at room temperature
- contributory factor to heart disease
- found in animal fats
what are unsaturated fatty acids?
do have double covalent bonds between their carbon atoms
- not all carbon atoms have the full number of hydrogen atoms
- lower melting point than saturated - liquid at room temperature
- found in plants
properties of triglycerides
- used as energy storage molecules
- insoluble in water
how are triglycerides a good energy storage molecule?
the long hydrocarbon tails of the fatty acids contain lots of chemical energy which yields twice as much energy per gram than glucose etc (carbohydrates)
how are triglycerides insoluble and why is that good?
it doesn’t affect water potential - no osmotic effect. fatty acid tails are hydrophobic - the tails face inwards, shielding themselves from water with their glycerol heads
what are phospholipids made from?
similar to triglycerides, made from 1 molecule of glycerol, 2 fatty acids and a phosphate group
where are phospholipids found?
cell membranes
which one is hydrophillic/hydrophobic - phosphate group/fatty acid tail?
phosphate group = hydrophillic
fatty acid tails = hydrophobic
what are the properties of phospholipids?
make up the bilayer of cell membranes (control what enters/leaves cell)
head = hydrophillic, tail = hydrophobic
how do they form a bilayer?
form a double layer with the heads facing out towards water - centre of the bilayer is hydrophobic so water-soluble substances can’t pass through it - the membrane acts as a barrier to those substances
how do you carry out the emulsion test for lipids?
- shake the test substance with ethanol for about a minute
- pour the solution into water
- any lipid will show up as a milky emulsion
- the more lipid there is, the more noticeable the milky colour will be
what should you keep ethanol away from?
open flames
how does the emulsion test for lipids work?
- ethanol dissolves the lipids
- lipids don’t dissolve in water - so when water is added and shaken, the lipids collect together to form an emulsion of lipid droplets in the water
