lipids

Question 1

solubility of lipids

Answer 1

insoluble in water and polar solvents
soluble in non-polar solvents

Question 2

4 functions of lipids

Answer 2

storage
- stores energy in fats and oils

structural
- protection
- insulation
- membranes

metabolism

industrial uses

Question 3

structure of fatty acids

Answer 3

hydrophobic hydrocarbon tail - non-polar
hydrophilic carboxyl group head - polar

Question 4

short chain fatty acids

Answer 4

2-5 carbon atoms
byproduct of fermentation
weak acids
- some polar properties

Question 5

long chain fatty acids

Answer 5

more than 5 carbons
naturally occurring in even number of carbons
saturated or unsaturated
- very little polar properties

Question 6

examples of short chain fatty acids (4)

Answer 6

2 - ethanoic acid - acetic acid
3 - propanoic acid - propionic acid
4 - butanoic acid - butyric acid
5 - pentanoic acid - valeric acid

Question 7

examples of long chain fatty acids (2)

Answer 7

saturated

16 - hexadecanoic acid - palmitic acid - 60.7
18 - octadecanic acid - stearic acid - 69.6

unsaturated

18:1 delta 9 - oleic acid - 16
18:2 delta 9,12 - linoleic acid - -5
18:3 delta 9,12,15 - a-linolenic acid - -11

Question 8

saturated fatty acids

Answer 8

no c=c double bonds
packed closely and interact
longer chain = more interactions
increase melting point when longer

eg hexdecanoic acid
octadecanic acid

Question 9

unsaturated fatty acids

Answer 9

1 or more c=c double bond
not straight, bond creates kink
cannot pack closely so fewer interactions
each double bond lowers melting point

cis or trans configurations
trans - hydrogen placed across double bond
cis - hydrogen on same side of double bond (normal)

eg oleic acid
linoleic acid
a-linolenic acid

Question 10

structure of triacylglycerols

Answer 10

3 fatty acids joined to a glycerol
by an ester bond

neutral molecules
used a energy stores
- seeds of oilseed plants
- adipose tissue of animals

hydrogen of hydroxyl group of glycerol reacts with OH of fatty acid

Question 11

why do tags make an efficient energy store? (4)

Answer 11

high energy in low weight
- long hydrocarbon chains give high energy

high energy in low volume
- neutral, packed closer than charged molecules, less volume

readily stored and released in hydrolysis and condensation

stores easily distinguish from surrounding material
- non-polar hydrophobic creates lipid droplets

Question 12

4 reactions of triacyglycerols

Answer 12

hydrolysis
iodination
saponification
hydrogenation

Question 13

hydrolysis of triacyglycerols

Answer 13

breaking of a covalent bond by the addition of water

essential before energy can be obtained
catalysed by specific lipase enzymes
broken down into glycerol and 3 fatty acid chains

Question 14

iodination of triacyglycerols

Answer 14

iodine reacts with double bonds in unsaturated chains

interactions breaks double bond and iodine atom bound to each carbon
(hydrogen removed)

Question 15

saponification of triacyglycerols

Answer 15

formation of soap by heating a triacylglycerol with alkali
fatty acids released

occurs when react with strong bases
releases glycerol molecule

forms salts of fatty acids known as soap

Question 16

salts of fatty acids produced in saponification

Answer 16

soap formed is amphipathic

allows molecules to form micelles
hydrophobic chains pack together inside
hydrophilic face outwards towards solvent

gives soap its cleaning properties
dirt enclosed within micelle

Question 17

hydrogenation of triacyglycerols

Answer 17

hydrogen reacts with hydrocarbon chain
double bond broken and hydrogen attaches

removes double bond
increases proportion of saturated fatty acids
increases melting point

Question 18

use of hydrogenation

Answer 18

transform oil and fats that are liquid at room temperature - hardened

partial hydrogenation used to improve shelf life
cis double bond converted to trans double bond
= trans fatty acids