1.3 lipids

Question 1

name the two groups of lipids

Answer 1

triglycerides and phospholipids

Question 2

describe the structure of a fatty acid ( RCOOH )

Answer 2

• variable R group + hydrocarbon chain ( saturated or unsaturated )
• COOH = carboxyl group

Question 3

describe the difference between saturated and unsaturated fatty acids

Answer 3

• saturated have no C=C double binds in their hydrocarbon chains, all carbons are fully saturated with hydrogen
• unsaturated have one or more C=C double bond in hydrocarbon chain creating bends/kinks

Question 4

describe how triglycerides form

Answer 4

• 1 glycerol molecule and 3 fatty acids
• condensation reaction
• removing 3 water molecules
• forming 3 ester bonds

Question 5

what is the function of triglycerides

Answer 5

energy storage

Question 6

how to the properties of triglycerides related to their function

Answer 6

• high ratio of C-H bonds to carbon atoms in hydrocarbon chain so used in respiration to release more energy than same mass of carbohydrates
• hydrophobic/non polar fatty acids which are insoluble in water ( clump together as droplets ) so no effect on water potential of cell ( or can be used for waterproofing )

Question 7

describe the difference between the structure of triglycerides and phospholipids

Answer 7

one of the fatty acids of a triglyceride is substituted by a phosphate containing group

Question 8

what is the function of phospholipids

Answer 8

to form a bilayer in the cell membrane, allowing diffusion of lipid soluble ( non polar ) or very small substances and restricting movement of water soluble ( polar ) or larger substances

Question 9

how do the properties of phospholipids relate to their structure

Answer 9

• phosphate heads are hydrophilic so are attracted to water so point to water ( in aqueous environments ) either side of the membrane
• fatty acid tails are hydrophobic meaning they are repelled by water so point away from water to interior of membrane

Question 10

describe the test for lipids

Answer 10

1. add ethanol, shake ( to dissolve lipids ) and then add water
2. positive = milky white emulsion