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BIOMOLECULES 1

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 Introduction
● Biomolecules are of several types

1. Carbohydrates
2. Proteins
3. Enzymes
4. Vitamins
5. Nucleic acids
6. Hormones
 Carbohydrates
● Originally, the name carbohydrate was given to the compounds
pertaining to general formula Cx(H20)y, and they were
considered to be hydrates of carbon.
 Carbohydrates
1. Polyhydroxy aldehydes or ketones
2. They are also known as saccharides
 Carbohydrates Classification
Carbohydrates

monosaccharides Oligosaccharides Polysaccharides

Yield 2-10 monosaccharides on Yield large number of

Cannot be hydrolysed further,
hydrolysis (C6H10O5)n , where n = monosaccharides on hydrolysis
(CH2O)n where n = 3-7 eg glucose,
2-10 (C6H10O5)n , where n = 100 -3000
fructose, ribose etc
Eg sucrose, maltose etc Eg starch, cellulose etc
 Sugars & non-sugars
● Sugars and non sugars….
● Carbohydrates which are sweet in taste are collectively called
sugars while those which are not sweet are called non-sugars.
Monosaccharides and disaccharides are sugars but
polysaccharides are non-sugars
 Reducing & non-reducing sugars
● All those carbohydrates which reduce Fehling's solution and
tollens reagent are referred to as reducing sugars.
● All monosaccharides whether aldose or ketose are reducing
sugars.

● In disaccharides, if the reducing groups of monosaccharides i.e.

aldehydic or ketonic groups are bonded, these are non-reducing
sugars e.g. Sucrose.
● On the other hand, sugars in which these functional groups are
free, are called reducing sugars. for example. maltose and
lactose.
Preparation of glucose
● From sucrose (cane sugar):

H+
C12H22O11 + H2O C6H12O6 + C6H12O6

Glucose Fructose

● From starch:

H+
(C12H10O5)+ nH2O nC6H12O6
393K: 2-3 atm

starch or Glucose
cellulose
Structure of glucose/ Important Reactions

CHO
HI, Δ
I
CH3-CH3-CH2-CH2-CH2-CH3
(CHOH)4
I n-hexane
CH2OH
 Structure of glucose/ Important Reactions
● Glucose reacts with hydroxylamine to form an oxime and adds a
molecule of hydrogen cyanide to give cyanohydrin. These
reactions confirm the presence of a carbonyl group (>C = O) in
glucose
CN

CHO NH2 OH CH N - OH CHO CH

I
I I HCN
I OH
(CHOH)4
(CHOH)4 (CHOH)4 (CHOH)4
I
I I I
CH2OH
CH2OH CH2OH CH2OH
 Structure of glucose/ Important Reactions
● Glucose gets oxidised to six carbon carboxylic acid gluconic
acid) on reaction with a mild oxidising agent like bromine water.
This indicates that the carbonyl group is perfect as an aldehyde
group
CHO
Br2, water COOH
I
I
(CHOH)4
(CHOH)4
I
I
CH2OH
CH2OH
Gluconic acid
 Structure of glucose/ Important Reactions
● On oxidation with nitric add, glucose as well as gluconic acid
both yield a dicarboxylic acid, saccharic acid. This Indicates the
presence of a primary alcoholic (-OH) group In glucose.

CHO oxidation COOH oxidation

COOH
I
I I
(CHOH)4
(CHOH)4 (CHOH)4
I
I I
CH2OH
COOH CH2OH
Saccharic acid
gluconic acid
 Structure of glucose/ Important Reactions
● Acetylation of glucose with acetic anhydride gives glucose
pentaacetate which confirms the presence of five-OH groups.

CHO Acetic anhydride

CHO O
I
I II
(CHOH)4
(CH-O-C-CH3)4
I O
I II
CH2OH
CH2-O-C-CH3
Gluconic acid
Structure of glucose
Which reagent is used to convert glucose into saccharic acid

A. Br2/H2O
B. Nitric acid
C. Alkaline solution of iodine
D. Ammonium hydroxide
Which gives red colour with Fehling’s solution?

A. Glucose
B. Cellulose
C. Benzaldehyde
D. Cane sugar
PYQ 2023
 PYQ 2023
Q9 - 27 July - Shift 2
Match List-I with List-II

List-I List-II
(A) Glucose + HI (I) Gluconic acid
(B) Glucose + Br2 water (II) Glucose pentacetate
(C) Glucose + acetic anhydride (III) Saccharic acid
(D) Glucose + HNO3 (VI) Hexane

Choose the correct answer from the options given below:

(A) (A)-(IV), (B)-(I), (C)-(II), (D)-(III)
(B) (A)-(IV), (B)-(III), (C)-(II), (D)-(I)
(C) (A)-(III), (B)-(I), (C)-(IV), (D)-(II)
(D) (A)-(I), (B)-(III), (C)-(IV), (D)-(II)
Structure of glucose/ Important Reactions
 Configuration of glucose

Glucose is correctly named as D(+)-glucose. ‘D' before the name of glucose

represents the relative configuration whereas ‘(+)’ represents dextrorotatory
nature of the molecule. It may be remembered that 'D’ and 'L' have no
relation with the optical activity of the compound.

(+)- glyceraldehyde (-)- glyceraldehyde

 Glucose (Dextrose or grape sugar), C6H12O6
All those compounds which can be chemically correlated to (+) Isomer of
glyceraldehyde are said to have D-configuration those which can be
correlated to (-) isomer of glyceraldehyde are said to have L-
configuration:
For assigning the configuration of monosaccharides. it is the lowest
asymmetric carbon atom which is compared.
CHO
CHO H OH
H OH OH H
H OH
CH2OH
H OH
D-(+)-glyceraldehyde CH2OH

D-(+)-Glucose
 Cyclic structure of glucose
● The open chain structure of glucose, could explain most of its
properties, but failed to explain the following properties

1. Despite having the aldehyde group, glucose does not give

Schiff’s test and it does not form the hydrogen sulfite addition
product with NaHSO3
2. The pentaacetate of glucose does not react with hydroxylamine
indicating the absence of free —CHO group
3. Glucose is found to exist in two different crystalline forms
which are named as α and β.
Cyclic structure of glucose
Cyclic structure of glucose
Structure of Fructose
Structure of Fructose

Fructose

● Fructose also has the molecular formula C6H1206

● It was found to contain a ketone functional group. It belongs to D-
series and is a Laevorotatory compound. Written as D-(-)-fructose.
Cyclic structure of fructose
1. As a ketohexose, fructose forms a 5-membered ring when the
hydroxyl on C-5 reacts with the carbonyl on C-2
 Epimers
Two sugars differing in configuration at a single asymmetric Carbon atom are known as
epimers.

They are also diastereomers

Epimers
Epimers
Disaccarides
 PYQ 2023
Q4 - 27 June - Shift 2
Given below are two statements.
Statemen-I: Maltose has two -D-glucose units linked at C1 and C4 and is
a reducing sugar.
Statement-II: Maltose has two monosaccharides: -D-glucose and -D-
glucose linked at C1 and C6 and it is a non-reducing sugar.
In the light of the above statements, choose the correct answer from the
options given below.
(A) Both Statement I and Statement II are true
(B) Both Statement I and Statement II are false
(C) Statement I is true but Statement II is false
(D) Statement I is false but Statement II is true
 PYQ 2023
Q5 - 28 June - Shift 2
When sugar 'X' is boiled with dilute H2SO4 in alcoholic solution, two
isomers 'A' and 'B' are formed. 'A' on oxidation with HNO3 yields saccharic
acid where as 'B' is laevorotatory. The compound 'X' is :
(A) Maltose (B) Sucrose
(C) Lactose (D) Strach
PYQ 2023
PYQ 2020
 PYQ
2020
NCERT
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Polysaccharides (NCERT Snip)
Polysaccharides (NCERT Snip)
Polysaccharides (NCERT Snip)
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