Carbohydrates

Question 1

What are carbohydrates

Answer 1

Made up of carbon, hydrogen, oxygen
Has carbonyl group (C=O) (exist in either form of ketone or aldehyde) and multiple hydroxyl groups (OH)

Question 2

Properties of monosaccharides

Answer 2

Colourless crystalline solids, freely soluble in water, insoluble in nonpolar solvents

Question 3

Uses of monosaccharides

Answer 3

1. Important energy sources (respiratory substrate) to produce ATP using cellular respiration
2. Building blocks for synthesis of disaccharides and polysaccharides
3. Raw material for synthesis of other organic molecules, eg nucleotides, amino acids, fatty acids

Question 4

Structure of monosaccharide?

Answer 4

All carbon atoms except one have OH group, carbon atom not attached to OH group is attached to carbonyl group (C=O)
Carbonyl group is either aldehyde (monosaccharide called aldose or Aldo sugar) or ketone group (monosaccharide called ketone or keto sugar)

Question 5

Why are aldo-monosaccharides strong reducing sugars

Answer 5

Aldehyde groups have carbonyl group on carbon atom 1, easily oxidised to carboxylic acids

Question 6

Aldo sugars vs keto sugars

Answer 6

Aldo sugars have carbonyl groups on carbon atom 1, keto sugars have carbonyl group on any of carbon atoms other than carbon atom 1

Question 7

What is anomeric carbon

Answer 7

Carbon atom bonded to 2 oxygen atoms, one in ring, one outside
(when carbon is in ring structure)

Question 8

how to represent monosaccharide?

Answer 8

• exist as linear or ring structures, which exist in dynamic equilibrium within cell
  ring structure more predominant, energetically more stable

RMB HOW TO DRAW RING, OPEN CHAIN STRUCTURE

Question 9

A vs b glucose

Answer 9

A-glucose has hydroxyl group bonded to anomeric carbon lying below plane of ring and vice versa

Question 10

Condensation reaction definition

Answer 10

When 2 monosaccharides form a disaccharide, involving loss of a single water molecule

Question 11

Glycosidic bond definition

Answer 11

Bond formed between anomeric carbon of one sugar unit and another carbon on the other sugar unit

Question 12

How is hydrolysis carried out

Answer 12

One molecule of water is added during hydrolysis via
1. Incubation with dilute acid at 100 degrees (acid hydrolysis)
2. Incubation with enzyme

Question 13

monosaccharides, disaccharide eg

Answer 13

mono - glucose, galactose, fructose
disaccharide - maltose, sucrose, lactose

Question 14

What are polysaccharides

Answer 14

Macromolecules with a few hundred to a few hundred thousand monosaccharides joined by glycosidic bonds
Two types of polysaccharides - storage materials / structural materials

Question 15

benedict’s test (principle, method and observation)

Answer 15

Principle: Benedict’s test makes use of the ability of a free carbonyl group in a reducing
sugar to reduce copper from Cu2+ to Cu+. Under alkaline conditions, copper (II) sulphate, which exists as a blue solution, is reduced to insoluble copper (I) oxide,
which exists as a brick-red precipitate
Observation: reducing sugar not present: soln blue (then use acid hydrolysis to break down sugar into reducing sugar before redoing test) increasing quantities, suspension gradually turns from green to yellow to orange then to brick-red or brown
Why?
- all reducing sugars can reduce other compounds, oxidised in process
- non reducing sugars(sucrose) have no free carbonyl group, cant participate in redox rxn

Question 16

Glycogen vs starch

Answer 16

Both consist of only a-glucose monomers
Amylose, amylopectin (in starch) and glycogen contains a-glucose joined by a(1,4) glycosidic bonds

Amylopectin and glycogen contains a-glucose joined by a(1,6) glycosidic bonds

Question 17

Diff in property of glycosidic bonds

Answer 17

A(1,4) glycoside bonds allow for formation of linear, unbranched chains
A(1,6) glycosidic bonds gives rise to branches in chain

Question 18

How is starch formed, Structure of starch, function

Answer 18

How is starched formed - Starch is formed from excess glucose synthesised via photosynthesis

Structure of starch:
- consists of a-glucose monomers only
- consists of unbranched amylose (10-30%) and branched amylopectin (70-90%)

Function
- serves as carbon source
- Stored in plant sells as starch grains either within chloroplasts, or within amyloplasts (specialised plastids for starch storage)

Question 19

Amylose

Answer 19

Unbranded chain that consists of hundreds to thousands of a-glucose residues joined by a(1,4) glycosidic bounds
Forms a helical structure that is compact
- 6 glucose units per turn of helix
- poorly soluble in water and does not exert osmotic influence in the cell as it is bulky

Question 20

starch test

Answer 20

Principle
- The centre of the starch helix is hydrophobic, where iodine in potassium iodide solution packs within core of the helix to give rise to a blue-black colouration

Method
Add 3 drops of iodine in dilute potassium iodide solution
to the sample solution

observation:
- Sample turns blue-black in colour -> presence of starch
- Sample remains yellow / brown in colour -> absence of starch.

Question 21

amylopectin

Answer 21

structure:
- consists of a-glucose molecules
- contains both a(1,4) glycosidic bonds and a(1,6) glycosidic bonds

property
- a(1,4) and a(1,6) -> branched
- many branch ends allow larger number of enzymes to act on it at any one time, easily hydrolysed (good energy source)
- extensive branching -> highly compact (twice as many glucose residues as amylose)

Question 22

Structure and function of starch

Answer 22

1. structure: Starch is a large molecule.
   Function: insoluble, does not affect the water potential within cells and living organisms.
2. structure: Starch is composed of several hundreds to thousands of glucose monomers.
   function: It acts as a large store of carbon (respiratory
   substrate).
3. Structure: Glucose units are linked by α(1,4) glycosidic bonds.
   Function: Starch may be easily hydrolysed by enzymes
   present in plants and most organisms.
4. Structure: Amylose molecules are helical in shape.
   Function: Amylose is compact (can store large amounts of starch molecules)

5 Structure:Amylopectin molecules are highly branched due to the presence of α(1,6)
glycosidic bonds.
Function: Amylopectin is compact. A large number of free ends are available for hydrolysis by amylase at any one time.

6 Structure: Anomeric carbon is involved in glycosidic bond formation, leaving few free anomeric hydroxyl groups.
Function: Starch is an unreactive and chemically stable compound

Question 23

glycogen structure

Answer 23

function:
- major form of storage polysaccharide in animals
- found mainly in the liver and skeletal muscle in the form of cytoplasmic granules
- In liver, it is used as a source of glucose to maintain blood sugar
levels
- In muscle, it serves as a fuel
source to generate ATP for muscle contraction.

Structure:
- It consists only of α-glucose.
- similar structure to amylopectin but it is more extensively branched -> more compact
- α(1,6) glycosidic bonds occur every 8 - 12 glucose units. (in amylopectin it is every 12-30 residues)
- A suspension of glycogen in water gives a red-violet colour with iodine in potassium iodide
solution.

Question 24

structure and function of glycogen

Answer 24

1. structure: Glycogen is a large molecule.
   Function: Since it is insoluble, it does not affect the water
   potential within cells and living organisms

2 structure: Glycogen is composed of several
hundreds to thousands of glucose monomers.
Function: It acts as a large store of carbon (respiratory
substrate)

3. structure: Glucose units are linked by α(1,4) glycosidic bonds.
   Function: α(1,4) glycosidic bonds in glycogen may be easily hydrolysed by enzymes glycogen phosphorylase
4. Structure: Glycogen is highly branched due to the presence of α(1,6) glycosidic bonds.
   Function: Glycogen is highly compact. A larger number of free ends are available for hydrolysis by amylase at any one time.

5 Structure: Anomeric carbon is involved in glycosidic bond formation, leaving few free anomeric hydroxyl groups.

Function: Glycogen is an unreactive and chemically-
stable compound.

Question 25

cellulose structure

Answer 25

- provides structural support - made of b-glucose, b-glycosidic bond formed between monomers - alternate monomers are inverted to obtain b(1,4) glycosidic bonds -> cellulose forms a long, unbranched straight chain - chains run parallel to each other and their hydroxyl groups (OH) project outwards from each chain - Extensive hydrogen bonds form between the protruding OH groups of neighbouring chains, allowing the establishment of rigid cross-links between chains - cross linked cellulose chains associate in groups to form microfibrils (ard 60-70 cellulose chains) -> associate with other, non cellulose polysaccharides, arranged in larger bundles to form macrofibrils

Question 26

properties of cellulose cell wall

Answer 26

1. High tensile strength that confers cellulose considerable stability, making it a valuable structural material. - As the cellulose fibres are laid down in different orientations in the different layers of the plant cell wall, they permit the cell wall to withstand forces exerted in all directions. 2. Full permeability to water and solutes, important for the proper functioning of plant cells. Cellulose is also an important food source for animals (ruminants, snails, insects), algae, bacteria and fungi, all of which possess the enzyme cellulase that catalyses the digestion of cellulose to glucose.

Question 27

function of cellulose (food source)

Answer 27

impt food source for animals, all of which possess the enzyme cellulase that catalyses the digestion of cellulose to glucose

Question 28

how structure of cellulose relates to support function

Answer 28

1. structure: Cellulose is a large molecule. function: Since it is insoluble, it makes a good structural material 2. structure: β-glucose units are linked by β(1,4) glycosidic bonds, which has a different molecular shape from α(1,4) glycosidic bonds found in amylose and amylopectin. function: - Few organisms produce cellulase. - Amylase can only hydrolyse α(1,4) glycosidic bonds found in starch. - Hence, cellulose is stable. 3. structure: - Alternate inverted β-glucose units linked by β(1,4) glycosidic bonds allow cellulose to form long, unbranched and straight chains. - Extensive hydrogen bonds form between parallel chains. - Straight parallel chains can be grouped into microfibrils, which eventually cluster into macrofibrils. function: Cellulose provides high tensile strength for structural support.

Question 30

What is a a(1,4) glycosidic bond

Answer 30

Involves anomeric carbon atom 1 with its hydroxyl group in a configuration