Carbohydrates

Question 1

Elements Contained

Answer 1

Hydrogen (H)
Oxygen (O)
Carbon (C)

Question 2

Carbohydrates

Answer 2

Organic molecules used as source of energy in all organisms and as structural materials in cell walls

Question 3

The General Formula for a carbohydrate

Answer 3

Cn(H2O)n

Question 4

The 3 main groups of carbohydrates

Answer 4

Monosaccharides - Mono=1
Disaccharides - Di=2
Polysaccharides - Poly=Many

Question 5

Monosaccharides

Answer 5

Monosaccharides are single sugar units that form the building blocks for the larger carbohydrates.

They are classified according to the number of carbons:

Trioses=3C eg glyceraldehyde

Pentoses=5C eg ribose, deoxyribose (in RNA/DNA)

Hexoses=6C eg alpha and beta glucose, fructose and galactose

Question 6

Glucose

Answer 6

• Is the most common monosaccharide
• Is a Hexose sugar with the formula C6H12O6
• exists in both straight chain and ringed form (rings form when glucose is dissolved in water)

Question 7

Isomer

Answer 7

Same chemical formulae but different structural formulae

Question 8

2 isomers of glucose

Answer 8

1) Alpha-Glucose

2) Beta-Glucose

Question 9

Disaccharides

Answer 9

Sugars formed when 2 monosaccharides join during condensation reaction.
The 3 we need to know are:

Glucose+Glucose=Maltose+Water

Glucose+Fructose=Sucrose+Water

Glucose+Galactose=Lactose+Water

Question 10

Chemical formula Disaccharide

Answer 10

C6H12O6=C12H22O11 + H2O

Question 11

Reducing sugars

Answer 11

All the monosaccharides and many of the disaccharides are reducing sugars

Question 12

Biochemical Test for Reducing Sugars

Answer 12

• Add Benedicts Reagent to a solution with water
• Heat
• Blue to Brick-Red colour

Question 13

Biochemical test for non-reducing sugar

Answer 13

• Hydrolyse/heat with acid (acid hydrolysis)
• Neutralise, with alkali/sodium hydrogen carbonate
• Add Benedicts Reagent
• Heat-Blue to Brick-Red colour

Question 14

Polysaccharides

Answer 14

Polysaccharides are all:
-Polymers of glucose
-Macromolecules
-Insoluble
The 4 polysaccharides we need to know are:
-Starch
-Glycogen
-Cellulose
-Chitin

Question 15

Starch

Answer 15

Starch is a polymer of Alpha-Glucose and made up of 2 chains-Amylose and Amylopectin

Question 16

Amylose

Answer 16

Amylose is formed by a series of condensation reactions that bond alpha glucose molecules together into a long chain forming many glyosidic bonds

Question 17

Amylopectin

Answer 17

Amylopectin consists of a straight chain of alpha glucose units with branch points occurring at approx. every twelfth glucose units the straight chain. The branch points form when carbon 6 of a glucose molecule positioned above the chain forms a glyosidic bond with carbon 1 of a glucose molecule positioned above the chain.

Question 18

Starch Biological Importance

Answer 18

Starch is only stored in plants as an energy store. Animals store glycogen. Starch is hydrolysed by the enzyme amylase

Question 19

Starch Structure

Answer 19

• Polymer of alpha-glucose
• made up of amylose and/or amylopectin
• so it has 2 polysaccharides
• glyosidic bonds/ 1-4 and 1-6 linkages
• amylose coil/starch coiled/amylopectin branched; not compact
• glucose all same way up
• consists of single chains

Question 20

Starches Function and Properties

Answer 20

Function:
-Energy store in plant cells only
Properties:
-Insoluble so doesn’t affect osmotic potential in cell
-Can’t diffuse out of cell
-Coiled making it compact so stored lots in small space
-Starch as few free ends for enzyme hydrolysis so it is an excellent long term storage molecule - not broken down quickly

Question 21

Biochemical test for starch

Answer 21

• Add iodine

- Turns from orange-brown to blue-black colour

Question 22

Glycogen

Answer 22

Its a polymer of a alpha-glucose and it is an energy store in animal cells mainly in the liver and skeletal muscles. Glycogen has a similar structure as amylopectin but there is significantly more branching

Question 23

Glycogen function and properties

Answer 23

Function:
-Energy store in animal cells only
Properties:
-Has many more branches so it can hydrolyse rapidly to meet the higher energy demands of animals

Question 24

Cellulose

Answer 24

Its a polymer of Beta-Glucose and it has structural role in plant cell walls

Question 25

Cellulose Structure

Answer 25

• Polymer of Beta-Glucose
• With 1-4 glyosidic bonds
• Adjacent glucose molecules are rotated by 180’/head up and head down
• Hydrogen bonds form between OH groups adjacent parallel chains/reference to cross linking
• Forming microfibrils
• Straight chain only/no branches; not parallel
• Cellulose (cross linked) in straight chains
• Linked with hydrogen bonds

Question 26

Cellulose functions and properties

Answer 26

Function:
-Structural role in plant cell walls
Properties:
-Strength or stability-long chains cross linked by hydrogen bonds
-Freely permeable due to spaces between fibres so water can pass to cell membrane

Question 27

Chitin Structure

Answer 27

• Polymer of beta-glucose

- It has some - OH groups replaced by nitrogen-containing acteylamine groups

Question 28

Chitin function and properties

Answer 28

Function:
-Structural role in forming the exoskeleton of many invertebrates and cell walls in fungi eg yeast
Properties:
-Strong-long chains cross linked by hydrogen bonds
-Waterproof
-Lightweight