Carbohydrates

Question 1

Description of carbohydrates

Answer 1

Compounds containing C,H &O

Contains C=O & -OH functional groups
( carboxyl & hydroxyl)

Includes sugars, starches & cellulose

Question 2

Role of carbohydrates

Answer 2

Primary source of energy for brain, erythrocytes and retinal cells

Nervous system depends on glucose from the extra cellular fluid (ECF) for energy

Nervous tissue is incapable of maintains normal function if the glucose concentration falls too low

Question 3

Classification of carbohydrates

Answer 3

1. Size of the base carbon chain
2. Location of the CO functional group
3. Number of sugar units
4. Stereochemistry of the compound

Question 4

Size of carbon chain base

Answer 4

Smallest carbohydrate is glyceraldehyde ( a triose )
Contains 3 sugars

Tetrose= 4 carbons 
Pentose= 5 carbons         
Hexose = 6 carbons

Question 5

Location of CO functional group

Answer 5

Two forms of carbohydrates are : Aldose & ketose

Aldose ( All the way at the end)

• terminal carbonyl group
• any CHO containing an aldehyde

Ketose ( a Key fits in the middle of a lock)

• carbonyl group in the middle , linked in to two other carbon atoms
• any CHO containing a ketose group

Question 6

Number of sugar units

Answer 6

Monosaccharides
1 sugar unit
Ex. Glucose. Fructose, galactose

Disaccharides
2 sugar units joined by a glycosidic linkage
Ex. Maltose, lactose, sucrose

Oligosaccharides
2-10 sugar units

poly saccharides
> 10 sugar units
Starch, glycogen, cellulose

Question 7

Stereochemistry

Answer 7

Different spatial arrangements around each asymmetrical carbon, will form stereoisomers

Same chemical formula with different orientation

Question 8

Reducing vs Non- reducing sugars

Answer 8

Sugars with free aldehyde or ketone group are capable of reducing other substances ( oxidation - reduction reaction)

When forming glycosidic links, if the bond is formed with a carbon , other than anomeric carbon, the compound remains a reducing agent
Ex. Glucose, maltose, fructose, lactose, galactose

If a bond is formed with the anomeric carbon ( carbon attached to the 2 oxygen ) thhen it results in a non- reducing sugar
No free ketone or aldehyde group
Ex. Sucrose

Question 9

Digestion of carbohydrates

Answer 9

Location Enzymes Food Product

Mouth. Salivary Starch. Some dextrins
amylase

Duedenum Pancreatic Starch Maltose
amylase Dextrins. Maltose

Jejunum. Sucrase Sucrose Glucose,fructose
Maltase Maltose Glucose,glucose
Lactase Lactose Glucose,galactose

• everything converts to glucose

Question 10

Digestion of carbohydrates

Answer 10

Galactose & fructose are converted to glucose

End product of all carbohydrates in food consumed becomes glucose

Carbohydrate chemistry = the chemistry of glucose