BIOMOLECLES CLASS 12 C B S E .pptx

Unit 14:BIO-MOLECULE
PART-I
PREPARED BY –BIKASH MEHER
PGT CHEMISTRY (B.ED ,PG ,M.PHIL IN CHEMISTRY)
JNV ,NUAPADA ,ODISHA ,IN ,766105
24/12/2022 1

Objectives
After studying this Unit, you will be able to:
explain the characteristics of biomolecules like
carbohydrates, proteins and nucleic acids and
hormones;
classify carbohydrates, proteins, nucleic acids and
vitamins on the basis of their structures;
explain the difference between DNA and RNA;
describe the role of biomolecules in bio-system.
24/12/2022 2

What are biomolecules?
Definition: A biomolecule is a chemical compound found in
living organisms. These include chemicals that are
composed of mainly carbon, hydrogen, oxygen, nitrogen,
sulfur and phosphorus. Biomolecules are the building blocks
of life and perform important functions in living organisms.
 The four major example of biomolecules are
carbohydrates, lipids, nucleic acids, and proteins.
24/12/2022 3

Your chapter is cover the following major content :
 Carbohydrates
 Proteins
 Enzymes
 Vitamins
 Nucleic Acids
 Hormones
24/12/2022 4

Carbohydrates : Carbohydrates may be defined as optically
active polyhydroxy aldehydes or ketones or compounds which produce
such units on hydrolysis. e.g., cellulose, glycogen, starch, etc.
starch
24/12/2022 5

Some of the carbohydrates, which are sweet in taste, are also called
sugars.
The most common sugar, used in our homes is named as sucrose
whereas the sugar present in milk is known as lactose.
 Carbohydrates are also called saccharides (Greek: sakcharon means
sugar).
sucrose
24/12/2022 6

14.1.1 Classification of Carbohydrates
24/12/2022 7

Polysaccharides are not sweet in taste, hence they are
also called non-sugars.
24/12/2022 8

Sugar : In general, monosaccharides and oligosaccharides
are crystalline solids, soluble in water, sweet in taste.
 They are collectively called sugars. e.g., glucose,
fructose, sucrose etc. They are of two types :
(i) Reducing sugars : Those carbohydrates which contain free aldehydic
or ketonic group and reduce Fehling’s solution and Tollen’s reagent are
known as reducing sugars. e.g., all monosaccharides, maltose.
(ii) Non-reducing sugars : Those carbohydrates which do not have free
aldehydic or ketonic group and do not reduce Fehling’s solution or
Tollen’s reagent are known as non-reducing sugars. e.g., sucrose.
24/12/2022 9

14.1.2Monosaccharides
Some monosaccharides with example are given in the table as shown below :
24/12/2022 10

14.1.2.1 Glucose
 Glucose occurs freely in nature as well as in the combined form. It is present in sweet fruits
and honey. Ripe grapes also contain glucose in large amounts.
Preparation of Glucose
1. From sucrose (Cane sugar): If sucrose is boiled with dilute HCl or H2SO4 in
alcoholic solution, glucose and fructose are obtained inequal amounts.
2. From starch: Commercially glucose is obtained by hydrolysis of starch by
boiling it with dilute H2SO4 at 393 K under pressure.
24/12/2022 11

Structure of Glucose
24/12/2022 12

The exact spatial arrangement of different —OH groups was
given by Fischer after studying many other properties. Its
configuration is correctly represented as I. So gluconic acid
is represented as II and saccharic acid as III.
24/12/2022 18

Glucose is correctly named as D(+)-glucose.
 ‘D’ before the name of glucose represents the
configuration, whereas ‘(+)’ represents
dextrorotatory nature of the molecule.
 It should be remembered that ‘D’ and ‘L’ have no
relation with the optical activity of the compound.
 They are also not related to letter ‘d’ and ‘l’.
The meaning of D– and L– notations is as follows in
next slide.
24/12/2022 19

Cyclic Structure of Glucose
24/12/2022 21

Among the facts that had still to be accounted for were the following:
(a) D-(+)-Glucose fails to undergo certain reactions typical of aldehydes. Although it is readily
oxidized, it gives a negative Schiff test and does not form a bisulfite addition product.
 In this qualitative test for the aldehyde
functional group, the development of a
purple or magenta colour upon the addition
of a few drops of the analyte to the
decolourized Schiff’s reagent confirms the
presence of aldehydes.
What is the Schiff’s Test?
 Schiff’s test is a chemical test used to check for the presence of aldehydes in a given
analyte. This is done by reacting the analyte with a small quantity of a Schiff’s reagent
(which is the product formed in certain dye formulation reactions such as the reaction
between sodium bisulfite and fuchsin). The structure of a decolourized Schiff’s reagent is
illustrated below.
24/12/2022 22

Schiff’s Test Mechanism
 The bisulfite and para-rosaniline react together to afford a decolourised adduct whose
central carbon is sulfonated. Now, the free & uncharged amine groups belonging to the
aromatic ring that react with the aldehyde group to form an aldimine. This aldimine group
is an excellent electrophile and, therefore, undergoes further reaction with the bisulfite
ion. Finally, a purple or magenta coloured bisulfite adduct is formed.
24/12/2022 23

(b) The pentaacetate of glucose does not react with hydroxylamine
indicating the absence of free —CHO group.
(c) Glucose is found to exist in two different crystalline forms which
are named as a and b. The a-form of glucose (m.p. 419 K) is obtained
by crystallisation from concentrated solution of glucose at 303 K while
the b-form (m.p. 423 K) is obtained by crystallisation from hot and
saturated aqueous solution at 371 K.
This behaviour could not be explained by the open chain
structure (I) for glucose. It was proposed that one of the —OH
groups may add to the —CHO group and form a cyclic hemiacetal
structure. It was found that glucose forms a six-membered ring in
which —OH at C-5 is involved in ring formation. This explains the
absence of —CHO group and also existence of glucose in two forms
as shown below. These two cyclic forms exist in equilibrium with
open chain structure.
24/12/2022 24

The two cyclic hemiacetal forms of glucose differ only
in the configuration of the hydroxyl group at C1,
called anomeric carbon (the aldehyde carbon before
cyclisation). Such isomers, i.e., a(alpha) form and
b(beta)-form, are called anomers.
24/12/2022 27

14.1.2.2 Fructose
Fructose is an important ketohexose.
It is obtained along with glucose by the
hydrolysis of disaccharide, sucrose.
 It is a natural monosaccharide found in
fruits, honey and vegetables.
In its pure form it is used as a sweetner. It is
also an important ketohexose.
24/12/2022 30

Structure of Fructose
24/12/2022 32

DISACCHARIDES
The two monosaccharides are joined together by an oxide linkage
formed by the loss of a water molecule. Such a linkage between
two monosaccharide units through oxygen atom is called
glycosidic linkage.
24/12/2022 36

BIOMOLECLES CLASS 12 C B S E .pptx

Recommended

Recommended

More Related Content

Similar to BIOMOLECLES CLASS 12 C B S E .pptx

Similar to BIOMOLECLES CLASS 12 C B S E .pptx (20)

Recently uploaded

Recently uploaded (20)

BIOMOLECLES CLASS 12 C B S E .pptx