lipids

Question 1

what is the elemental composition of lipids

Answer 1

oxygen, hydrogen, carbon

Question 2

what is the structure of saturated fatty acids

Answer 2

-each carbon atom is fully saturated with its full quota of hydrogen atoms

-no double bonds occur between the carbon atoms

Question 3

what is the consistency and melting point of saturated fatty acids

Answer 3

-solid at room temperature (18C)

-high melting point

Question 4

what are the sources of saturated fatty acids and give examples

Answer 4

-generally found in animal sources
-e.g. butyric acid in butter and stearic acid in meat

Question 5

what is the structure of monounsaturated fatty acids

Answer 5

-each carbon is not fully saturated with a full quota of hydrogen atoms

-there is one double bond between the carbon atoms

Question 6

what is the consistency and melting point of monounsaturated fatty acids

Answer 6

-soft or liquid at room temperature (18C)

-low melting point

Question 7

what are the sources of monounsaturated fatty acids and give examples

Answer 7

-generally found in plant and marine sources

-e.g. oleic acid in olive oil

Question 8

what is the structure of polyunsaturated fatty acids

Answer 8

-each carbon atom is not fully saturated with a full quota of hydrogen atoms

-there is more than one double bond between the carbon atoms

Question 9

what is the consistency and melting point of polyunsaturated fatty acids

Answer 9

-soft or liquid at room temperature (18C)

-lowest melting point of all the fatty acids

Question 10

what are the sources of polyunsaturated fatty acids and give examples

Answer 10

-generally found in plant and marine sources

-e.g. linoleic acid in nuts and linolenic acid in seeds

Question 11

what are essential fatty acids

Answer 11

essential fatty acids are acids that cannot be manufactured by the body and therefore must be obtained from food

Question 12

what are the sources of essential fatty acids

Answer 12

-nuts

-seeds

-olive oil

-oily fish

Question 13

what are the biological functions of essential fatty acids

Answer 13

-aid cell membrane formation, which is essential for growth

-reduce the risk of coronary heart disease by raising high-density lipoprotein which helps remove cholesterol from the blood and by lowering low-density lipoprotein which deposits cholesterol in the blood

Question 14

describe the structure of an omega-3 fatty acids

Answer 14

omega-3 fatty acids have a double bond between the third and fourth carbon atoms along their hydrogen chain

Question 15

what are the sources of omega-3 fatty acids

Answer 15

-oily fish

-seeds

-nuts

-fish oils

Question 16

what are the biological functions of omega-3 fatty acids

Answer 16

-reduce the risk of coronary heart disease, heart attacks and strokes by raising HDL and lowering LDL

-decrease the viscosity of blood, preventing clots or blockages in the coronary arteries

-aid foetal brain development during pregnancy as well as helping to improve memory and cognitive functioning throughout life

Question 17

what is the chemical structure of cis fatty aids

Answer 17

the hydrogen atoms on either side of the double bond are both above or both below the carbon chain

Question 18

what are the sources of cis fatty acids

Answer 18

naturally occurring in foods such as olive oil and oily fish

Question 19

what is the significance of cis fatty acids in the diet

Answer 19

generally good for health as they raise HDL while lowering LDL decreasing the risk of coronary heart disease

Question 20

what is the structure of trans fatty acids

Answer 20

the hydrogen atoms on either side of the double bond are on opposite sides of the carbon chain

Question 21

what are the sources of trans fatty acids

Answer 21

-the heating or frying of oils at high temperatures
-pastries and crisps

Question 22

what is the significance of trans fatty acids in the diet

Answer 22

generally bad for health as they lower HDL while raising LDL increasing the risk of coronary heart disease

Question 23

what are the properties of lipids

Answer 23

-solubility
-absorption of flavours
-emulsions
-hydrogenation
-rancidity
-plasticity

Question 24

explain solubility as a property of lipid

Answer 24

lipids are insoluble in water. they are soluble in solvents such as ether and benzene

Question 25

explain absorption of flavours as a property of lipid

Answer 25

lipids absorb flavours easily, e.g. chilli oil

Question 26

explain heating lipids as a property of lipid

Answer 26

melting point: solid fats melt when heated to 30-40C smoke point: if lipids are heated to 200C or 250C they begin to decompose causing the glycerol to separate from the fatty acids. glycerol is then broken down into acrolein and produces a blue smoke or haze and a harsh smell -flash point: extreme overheating of lipids to 310C and 325C causes vapour to be released that can spontaneously catch on fire

Question 27

explain emulsion as a property of lipid

Answer 27

an emulsion is a colloidal solution, formed when two immiscible liquids are forced to mix together. emulsion can be described as water in oil emulsions or oil in water emulsion

Question 28

what is water in oil emulsion

Answer 28

e.g. butter, margarine. tiny droplets of water are dispersed throughout oil or fat

Question 29

what is oil in water emulsion

Answer 29

e.g. milk, mayonnaise. tiny droplets of oil are dispersed throughout the water

Question 30

what is temporary emulsion

Answer 30

formed when the two immiscible liquids, e.g. vinegar and oil are in vinaigrette, are shaken vigorously. if left to stand they will seperate

Question 31

what is permanent emulsion

Answer 31

formed when an emulsifier is added to two immiscible liquids, preventing them from separating, e.g. vinegar and oil in mayonnaise

Question 32

what is emuslifiers

Answer 32

are molecules that have a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail. when an emulsifier is added to a mixture of two immiscible liquids the hydrophilic head attaches itself to the water and the hydrophobic tail attaches itself to the oil. this prevents the liquids from separating, creating a permanent emulsion

Question 33

what is a stabilisers

Answer 33

are long-chained molecules that helps to maintain emulsions by separating the oil droplets and preventing them from coalescing

Question 34

explain hydrogenation as a property of lipid

Answer 34

is a process whereby hydrogen gas, in the presence of a nickel catalyst is forced through the double bond of an unsaturated oil, converting the unsaturated oil into a saturated solid fat, e.g. used in the production of margarine

Question 35

explain rancidity as a property of lipid

Answer 35

is the spoilage or decomposition. this results in an unpleasant odour and taste. there are two types of rancidity: oxidative and hydrolytic rancidity

Question 36

what is oxidative rancidity

Answer 36

occurs when oxygen in the air combines with the carbons in a double bond of the unsaturated fatty acid

Question 37

what is hydrolytic rancidity

Answer 37

occurs when enzymes or bacteria break down lipids into glycerol and fatty acids

Question 38

explain plasticity as a property of lipid

Answer 38

describes how soft, flexible and shapable a fat is at a given temperature. it is determined by the degree of saturation, the more saturated fatty acids present, the more solid the lipid

Question 39

what is the biological functions of lipids

Answer 39

-lipids supply the body with heat and energy, helping to keep the body temperature at 37C and providing energy for all activities -lipids form a protective layer that surrounds delicate organs, e.g. the kidneys -lipids supply the body with the fat-soluble vitamins A,D,E and K which are necessary for overall health -excess lipid intake is stored as adipose tissue under the skin. this insulates the body and acts as an energy reserve