3.1.3 Lipids

Question 1

what elements do lipids contain?

Answer 1

carbon, hydrogen, oxygen

Question 2

what are triglycerides made from?

Answer 2

one molecule of glycerol + three molecules of fatty acids

Question 3

how do triglycerides form?

Answer 3

formed by the condensation of one molecule of glycerol + 3 molecules of fatty acids

Question 4

what bonds do triglycerides form?

Answer 4

ester bonds

Question 5

where do triglycerides store energy in?

Answer 5

plants, animals and some bacteria

Question 6

what are the tails made of on fatty acids?

Answer 6

hydrocarbons and one carboxylic acid

Question 7

what does the tails being hydrophobic mean?

Answer 7

it repels water molecules which make lipids insoluble in water

Question 8

what is a hydrocarbon chain also known as in a fatty acid?

Answer 8

R

Question 9

how many different fatty acids are there?

Answer 9

70

Question 10

what are saturated fatty acids?

Answer 10

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

Question 11

what are unsaturated fatty acids?

Answer 11

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

Question 12

properties of triglycerides

Answer 12

• used as energy storage molecules
• insoluble in water

Question 13

how are triglycerides a good energy storage molecule?

Answer 13

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)

Question 14

how are triglycerides insoluble and why is that good?

Answer 14

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

Question 15

what are phospholipids made from?

Answer 15

similar to triglycerides, made from 1 molecule of glycerol, 2 fatty acids and a phosphate group

Question 16

where are phospholipids found?

Answer 16

cell membranes

Question 17

which one is hydrophillic/hydrophobic - phosphate group/fatty acid tail?

Answer 17

phosphate group = hydrophillic
fatty acid tails = hydrophobic

Question 18

what are the properties of phospholipids?

Answer 18

make up the bilayer of cell membranes (control what enters/leaves cell)
head = hydrophillic, tail = hydrophobic

Question 19

how do they form a bilayer?

Answer 19

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

Question 20

how do you carry out the emulsion test for lipids?

Answer 20

1. shake the test substance with ethanol for about a minute
2. pour the solution into water
3. any lipid will show up as a milky emulsion
4. the more lipid there is, the more noticeable the milky colour will be

Question 21

what should you keep ethanol away from?

Answer 21

open flames

Question 22

how does the emulsion test for lipids work?

Answer 22

• 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