Biomolecules

Question 1

Carbohydrates: definition

Answer 1

Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketonesm or large polymeric molecules which on hydrolysis yield polyhydroxy aldehydes and polyhdroxy ketones.

Question 2

Monosaccharides: Definition

Answer 2

Carbohydrates which cannot be decomposed by further hydrolysis to give simpler carbohydrates

Question 3

Monosaccharides: General formula + examples

Answer 3

(CH₂O)_n
n = 3 - 7

C₆H₁₀O₆
Glucose, fructose, galactose
C₆H₁₀O₅: ribose

Question 4

Oligosaccharides: definition

Answer 4

Carbohydrates which upon hydrolysis give a definite number (2-10) of molecules of monosaccharides are called oligosaccharides

Question 5

Disaccharides

Answer 5

Oligosaccharides

Carbohydrates which upon hydrolysis give two units of the same or different monosaccharides.

E.g. C₁₂H₂₂O₁₁
Maltose, sucrose, lactose

Question 6

Trisaccharides

Answer 6

Oligosaccharides

Carbohydrates which upon hydrolysis give three units of the same or different monosaccharides.

E.g. C₁₈H₃₂O₁₆
Raffinose + 2H₂O —hydrolysis—> glucose + fructose + galactose

Question 7

Tetrasaccharide

Answer 7

Oligosaccharides

Carbohydrates which upon hydrolysis give four units of the same or different monosaccharides.

E.g. C₂₄H₄₂O₂₁
Stachyrose + 3H₂O —hydrolysis—> glucose + fructose + 2(galactose)

Question 8

Polysaccharides: definition, general formula, examples

Answer 8

The carbohydrates which upon hydrolysis give a large number of monosaccharide molecules are called polysaccharides

(C₆H₁₀O₅)_n
where n = 100 - 3000

E.g. starch, cellulose, glycogen

Question 9

Reducing sugars: Definition + example

Answer 9

Carbohydrates which are capable of reducing Tollen’s reagent and Fehling’s solution are called reducing sugars

E.g all monosaccharides and disaccharides except sucrose

Question 10

Non-reducing sugars

Answer 10

Carbohydrates unable to reduce Tollen’s reagent and Fehling’s solution are called non-reducing sugars

E.g. Sucrose

Question 11

Aldoses

Answer 11

Monosaccharides possessing an aldehyde group (-CHO) are called aldoses

Always present on terminal carbon atom

Question 12

Ketoses

Answer 12

Monosaccharides containing a keto group are called ketoses.

In naturally occurring ketoses, the keto group is present on the second carbon atom

Question 13

D-configuration

Answer 13

When the -OH group on the C atom adjacent to CH₂OH group lies on the right hand side in the Fischer projection, the monosaccharide has D-configuration

Question 14

L-configuration

Answer 14

When the -OH group on the C atom adjacent to CH₂OH group lies on the left hand side in the Fischer projection, the monosaccharide has L-configuration

Question 15

Structure of glucose

Answer 15

1. Presence of a straight chain of 6 carbon atoms
2. Presence of carbonyl group (>C=O)
3. Presence of aldehydic (-CHO) group
4. Presence of 5 hydroxyl (-OH) groups
5. Presence of primary alcoholic group

Question 16

Glucose structure: prove presence of straight chain of 6 carbon atoms

Answer 16

HI + heat
glucose -> n-hexane + water

Question 17

Glucose structure: prove presence of carbonyl group

Answer 17

rxn w hydroxylamine NH2OH
glucose -> oxime

Question 18

Glucose structure: prove presence of aldehydic group

Answer 18

[O] + Br water

Glucose-> Gluconis acid

Question 19

Glucose structure: prove presence of 5 -OH groups

Answer 19

acetic anhydride

glucose -> pentaacetate

Question 20

Presence of primary alcoholic group

Answer 20

oxidation with nitric acid

glucose -> saccharic acid