3.1.3 lipids

Question 1

What are lipids made from?

Answer 1

• made from a variety of different components but they all contain hydrocarbons
• the components they are made from relate to the lipid’s function

Question 2

name the 2 main groups of lipids

Answer 2

triglycerides and phospholipids

Question 3

triglyceride structure

Answer 3

• one molecule of glycerol with 3 fatty acids attached to it

Question 4

what are the two types of fatty acids?

Answer 4

saturated fatty acids and unsaturated fatty acids

Question 4

why are tryglycerides insoluble in water?

Answer 4

the fatty acids on them have long tails made of hydrocarbons, these tails are hydrophobic (repel water)

Question 5

what differs between saturated and unsaturated fatty acids

Answer 5

the difference is in their hydrocarbon tails (R groups)

Question 6

what makes fatty acids saturated?

Answer 6

• no double bonds between their carbon atoms

Question 7

what makes fatty acids unsaturated?

Answer 7

• have a double bond between carbon atoms, causes the chain to kink

Question 8

triglyceride formation

Answer 8

• formed by condensation reactions
• condensation reaction between a glycerol molecule and fatty acid (RCOOH) forms an ester bond, which releases a water molecule
• this process happens 2 times to form a triglyceride

Question 9

where are phospholipids found?

Answer 9

they are the lipids found in cell membranes

Question 10

phospholipid structure

Answer 10

• similar to triglycerides but one of the fatty acid molecules is replaced by a phosphate group

Question 11

what parts of the phospholipid are hydrophobic and what parts are hydrophilic?

Answer 11

-phosphate group is hydrophilic
- fatty acid tails are hydrophobic

Question 12

what are triglycerides mainly used as?

Answer 12

energy storage molecules

Question 13

why are triglycerides good as energy storage molecules?

Answer 13

the long hydrocarbon tails of the fatty acid contain lots of chemical energy so a lot of energy is released when they are broken down

Question 14

are triglycerides insoluble or soluble in water?

Answer 14

insoluble

Question 15

as a result of triglycerides being insoluble in water what does this mean?

Answer 15

they don’t affect the water potential of the cells and cause water to enter the cells by osmosis (which can cause them to swell) and are used for waterproofing

Question 16

What do triglycerides do in cells?

Answer 16

triglycerides bundle together as insoluble droplets in cells as the fatty acid tails are hydrophobic - the tails face inwards, shielding themselves from the water with their glycerol heads

Question 17

what do phospholipids make up?

Answer 17

the bilayer of cell membranes

Question 18

phospholipid bilayer structure

Answer 18

• heads are hydrophilic and tails are hydrophobic so they form a double layer with the heads facing outwards on both sides. Centre of bilayer is hydrophobic so water soluble substances can’t easily pass through it - membrane acts as a barrier to those substances

Question 19

what is the test for lipids

Answer 19

emulsion test

Question 20

describe the emulsion test

Answer 20

-shake test substance with ethanol for around a minute then pour the solution into water
-any lipids will show up as a milky emulsion
-the more lipids there are, the more noticeable the milky colour will be

Question 21

what is the general formula of a saturated fatty acid?

Answer 21

Cn H2n O2

Question 22

why are triglycerides good for thermal insulation?

Answer 22

slow conductor of heat = thermal insulation e.g. adipose tissue

Question 23

what function do triglycerides have in relation to their density?

Answer 23

less dense than water = buoyancy of aquatic animals