2.3 : Carbohydrates & Lipids

Question 1

what are the main elements in carbohydrates?

Answer 1

• carbon
• hydrogen
• oxygen

Question 2

what are monosaccharides?

Answer 2

the simplest form of a carbohydrate = simple sugar

Question 3

what are polysaccharides?

Answer 3

many monosaccharides combined through glycosidic bonds to form a lager carbohydrate (polysaccharide)

Question 4

what are disaccharides?

Answer 4

a polysaccharide with two or more monosaccharides with glycosidic linkages, condensed together

Question 5

what are isomers & examples?

Answer 5

• compounds that have the same component atoms in their molecules but different arrangements of the atoms.
• a-glucose & b-glucose

Question 6

what are optical isomers & examples?

Answer 6

• compounds that have the same chemical properties but different arrangements, creating mirror images of each other.
• L-glucose & D-glucose.

Question 7

what is the test for reducing sugars?

Answer 7

Benedict’s test.

Question 8

what are the characteristics and uses of cellulose (polysaccharide) & how is it’s stabilised in its structure?

Answer 8

• strong, insoluble, tough, slightly elastic.
• fibres as cotton, manufacture into paper, explosives, rayon fibres for clothes.
• it’s structure is strengthened & stabilised through hydrogen bonds between adjacent glucose molecules in the same strand & parallel strands (in fibres).

Question 9

what is starch made up of?

Answer 9

mixture of two polysaccharides :
-amylose : unbranched chain of thousands of linked
a-glucose units.
-amylopectin : shorter and branched chains of a-glucose units;

Question 10

what is a monomer?

Answer 10

a basic molecule that can react together with monomer molecules to form a repeating chains of polymers during polymerisation.

Question 11

what is a polymer?

Answer 11

a large molecule consisting of many identical monomers linked together via covalent bonds.

Question 12

what are phospholipids?

Answer 12

molecule that has a hydrophilic head with a phosphate group and two hydrophobic tails from fatty acids joined by an alcohol group.

Question 13

what is the difference between saturated & unsaturated lipids?

Answer 13

• saturated lipids : compounds that have single carbon bonds.
• unsaturated lipids : compounds that have double carbon-carbon bonds.

Question 14

what are lipids built from 1) saturated and 2) unsaturated fatty acids called & examples?

Answer 14

1) saturated fats -butter, lard, cocoa butter.

2) unsaturated fats -olive oil.

Question 15

(unsaturated fatty acids) what are monounsaturated & polyunsaturated fatty acids?

Answer 15

• monounsaturated fatty acids : when there is a single double bond in a carbon chain of a fatty acid.
• polyunsaturated fatty acid : when there are two or more double bonds in a carbon chain of a fatty acid.

Question 16

why do fats with unsaturated fatty acids have a lower melting point?

Answer 16

as the unsaturated hydrocarbon tail doesn’t pack so closely in comparison to saturated fats –> meaning that molecules are able to vibrate more due to more space between molecules = melt faster.

Question 17

what is the difference between CIS and TRANS fatty acids?

Answer 17

• CIS : two parts of the hydrocarbon chain are on the same side of the double bond.
• TRANS : two parts of the hydrocarbon chain are on opposite sides.

Question 18

what do diets rich in trans fats cause?

Answer 18

cause an increase in levels of Low-density lipoprotein (LDL) cholesterol in blood = bad cholesterol.
(increased risk of coronary heart disease - block arteries & veins - lack of blood supply)

Question 19

what are omega-3 fatty acids & where are the double bonds located?

Answer 19

-a naturally occurring polyunsaturated fatty acids.
(polyunsaturated = more than one double bond in backbone)
-the first double bond is always between the 3rd and 4th carbon atom from opposite end (=omega end) of a hydrocarbon chain to carboxyl group.

Question 20

why are omega-3 fatty acids beneficial?

Answer 20

• produce hormones that regulate blood clotting, contractions, relaxation of artery walls.
• lower levels of HDL cholesterol –> lower risk of heart disease, etc.
• reduce triglycerides –> large amount = harden & thicken artery walls (stroke, etc.)

Question 21

what are the applications of lipids?

Answer 21

• subcutaneous fats –> acts as a buoyancy aid & thermal insulation
• water proofing of hair and feathers –> oily secretions of sebaceous glands (skin of mammals) = water repellent
• electrical insulation –> myelin lipid in membranes of Schwann cells –> form sheaths around long fibres of nerve cells –> electrically isolates cell plasma membrane & facilitates conduction of nerve impulses there.