Biomolecules class 12 chemistry

Hlo

1. Biomolecules
•Unit XIV:
•Carbohydrates - Classification (aldoses and ketoses),
monosaccharides (glucose and fructose), D-L configuration
oligosaccharides (sucrose, lactose, maltose), polysaccharides
(starch, cellulose, glycogen); Importance of carbohydrates.
•Proteins -Elementary idea of - amino acids, peptide bond,
polypeptides, proteins,
•structure of proteins - primary, secondary, tertiary structure and
quaternary structures
•(qualitative idea only), denaturation of proteins; enzymes.
Hormones - Elementary idea
•excluding structure.
•Vitamins - Classification and functions.
•Nucleic Acids: DNA and RNA.

2. BIOMOLECULE

3. •Biomolecules include both micromolecules,
e.g. amino acids, nitrogenous bases, fatty
acids, sugar, etc. and macromolecules, such
as carbohydrates, proteins, lipids and nucleic
acids.

4. List of concepts
•Carbohydrates
•Proteins
•Enzymes
Vitamins
•Nucleic Acids
•Hormones

5. •Carbohydrates is a class of compounds that include
polyhydric aldehydes and ketones and large number of
other polymeric molecules that yield these on
hydrolysis, e.g., sugars, glycogen, cellulose, starch, etc.
•The general formula of carbohydrate is Cx(H2O)y
• Depending upon their behaviour on hydrolysis,
carbohydrates are further divided into
• three types:
• Monosaccharides
•disaccharides
•polysaccharides

6. Monosaccharides
• A carbohydrate that cannot be hydrolysed
further to give simpler unit of polyhydroxy
aldehyde or ketone is called a
monosaccharide.
•For example glucose, fructose, ribose, etc.
•About 20 monosaccharides are known to
occur in nature.

7. Oligosaccharides
•Carbohydrates that yield two to ten monosaccharide units,
on hydrolysis, are called oligosaccharides.
•They are further classified as disaccharides, trisaccharides,
tetrasaccharides, etc.,
•depending upon the number of monosaccharides, they
provide
•on hydrolysis. Amongst these the most common are
disaccharides.
•The two monosaccharide units obtained on hydrolysis of a
disaccharide may be same or different.
•For example, one molecule of sucrose on hydrolysis gives
one molecule of glucose and one molecule of fructose
•Maltose gives two molecules of only glucose.

8. Polysaccharides
•Carbohydrates which yield a large number of
•monosaccharide units on hydrolysis are called
polysaccharides.
•Some common examples are
• starch, cellulose, glycogen, gums, etc.
•Polysaccharides are not sweet in taste, hence
they are also called non-sugars.

9. Monosaccharides
•Monosaccharides are further classified on the
basis of number of carbon atoms and the
functional group present in them.
• If a monosaccharide contains an aldehyde
group, it is known as an aldose
•if it contains a keto group, it is known as a
ketose.

10. 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.

11. Preparation of Glucose
•From sucrose (Cane sugar):
If sucrose is boiled with dilute HCl or H2SO4 in
alcoholic solution, glucose and fructose are
obtained in equal amounts.

12. From starch:
•Commercially glucose is obtained by
hydrolysis of starch by boiling it with dilute
H2SO4 at 393 K under pressure

13. Structure of Glucose
•Glucose is an aldohexose and is also known as
dextrose.
•It is the monomer of many of the larger
carbohydrates, namely starch, cellulose.
It is probably the most abundant organic
compound on earth.

15. the structure given below on the basis of the following
evidences:
1. Its molecular formula was found to be C6H12O6.
2. On prolonged heating with HI, it forms n-hexane,
suggesting that all the six carbon atoms are linked in a
straight chain.

16. 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.

17. 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 present as an aldehydic
group.

18. Acetylation of glucose with acetic anhydride gives glucose
pentaacetate which confirms the presence of five –OH groups.

19. On oxidation with nitric acid, 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.

20. •Glucose is correctly named as D(+)-glucose. ‘D’
before the name of glucose represents the
configuration
• ‘(+)’ represents dextrorotatory nature of the
molecule.

21. Cyclic Structure of Glucose
•The structure (I) of glucose explained most of its
properties but the following reactions and facts
could not be explained by this structure.
1 Despite having the aldehyde group, glucose does
not give Schiff’s test and it does not form the
hydrogensulphite addition product with NaHSO3.
2. The pentaacetate of glucose does not react with
hydroxylamine indicating the absence of
free —CHO group.

22. 3. Glucose is found to exist in two different
crystalline forms which are named as alfa and
beta. The alfa-form of glucose (m.p. 419 K) is
obtained by crystallisation from concentrated
solution of glucose at 303 K while
the beta-form (m.p. 423 K) is obtained by
crystallisation from hot and saturated aqueous
solution at 371 K

24. Anomers
•The two cyclic hemiacetal forms of glucose
differ only in the configuration of the hydroxyl
group at C1, called anomeric carbon Cyclic
Structure of Glucose (the aldehyde carbon
before cyclisation).
•Such isomers, i.e., alfa -form and beta -form,
are called anomers.

25. The six membered cyclic structure of glucose is called
Pyranose structure

26. 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.

27. •Fructose also has the molecular formula
C6H12O6 and on the basis of its reactions it was
found to contain a ketonic functional group at
carbon number 2 and six carbons in straight
chain as in the case of glucose.

29. •It also exists in two cyclic forms which are
obtained by the addition of —OH at C5 to the
(c=o ) group.
•The ring, thus formed is a five membered ring
and is named as furanose with analogy to the
compound furan.

31. The cyclic structures of two anomers of fructose are represented by
Haworth structures as given.

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.
Exmple - Sucrose,maltose and lactose.

33. •(i) Sucrose: One of the common disaccharides
is sucrose which on
•hydrolysis gives equimolar mixture of D-(+)-
glucose and D-(-) fructose

34. •Since the reducing groups of glucose and
fructose are involved in
•glycosidic bond formation, sucrose is a non
reducing sugar.

36. Maltose
•maltose is composed of two a-D-glucose units
in which C1 of one glucose (I) is linked to C4
of another glucose unit (II).
It is a reducing sugar.

38. Lactose
•It is more commonly known as milk sugar
since this disaccharide is found in milk. It is
composed of beta-D-galactose and beta-D-
glucose.
•The linkage is between C1 of galactose and C4
of glucose
•it is also a reducing sugar.

40. Polysaccharides
•Polysaccharides contain a large number of
monosaccharide units joined together by
glycosidic linkages.
•Example are
•starch
•cellulose
• glycogen

41. Starch
•Starch is the main storage polysaccharide of
plants.
•It is the most important dietary source for human
beings.
•High content of starch is found in cereals, roots,
tubers and some vegetables.
•It is a polymer of alfa-glucose and
• consists of two components—
Amylose and Amylopectin..

42. Amylose
•Amylose is water soluble component
•which constitutes about 15-20% of starch.
Chemically amylose is a long unbranched
chain with 200-1000 alfa-D-(+)-glucose units
•held together by C1– C4 glycosidic linkage.

43. Amylopectin
•Amylopectin is insoluble in water and
constitutes about 80- 85% of starch.
• It is a branched chain polymer of a-D-glucose
units in which chain is formed by C1–C4
glycosidic linkage whereas
•branching occurs by C1–C6 glycosidic linkage

45. Cellulose
•Cellulose occurs exclusively in plants and it is
the most abundant organic substance in plant
kingdom.
•It is a predominant constituent of cell wall of
plant cells.
•Cellulose is a straight chain polysaccharide
composed only of beta-D-glucos

46. Glycogen
•The carbohydrates are stored in animal body
as glycogen.
•It is also known as animal starch because its
structure is similar to amylopectin and is
rather more highly branched.
• It is present in liver, muscles and brain.
•When the body needs glucose, enzymes break
the glycogen down to glucose.
•Glycogen is also found in yeast and fungi.

47. Tests for carbohydrates:

•For this, a Molisch test is performed.
• Molisch reagent, a 10% alcoholic solution of
alpha naphthol, is added to an aqueous
solution of carbohydrates, followed by
concentrated sulphuric along the sides of the
tube. As a result, a violet ring is formed at the
junction of two layers.

48. Importance of Carbohydrates
•Carbohydrates are essential for life in both
plants and animals.
•Carbohydrates are used as storage molecules
as starch in plants and glycogen in animals.
•They provide raw materials for many
important industries like textiles,paper,
lacquers

49. •Which of the following polymer is stored in
the liver of animals?
•(a) Amylose (b) Cellulose
(c) Amylopectin (d) Glycogen

50. Which of the following pairs represents anomers?

51. •Glucose reacts with hydroxylamine to form an
oxime. This confirms the presence of
(a) straight chain of six carbon atoms
(b) carbonyl group
(c) primary alcoholic group
(d) secondary alcoholic group

52. •The symbols D and L in the name of
Carbohydrate represents
(a) Dextro rotatory nature
(b) Laevo rotatory nature
(c) The relative configuration of a particular
isomer
(d) The optical activity of compounds

53. Proteins
•The term ‘Protein’ is derived from the Greek
word ‘Protein’, which means ‘Primary
importance’.
•Proteins are higher in molecular weight,
complex bio-polymers of alpha-amino acids
found in all living organisms.
•They occur in all parts of the body and form
the fundamental basis of the structure and
functions of life.

54. •The primary sources of proteins are milk, cheese, pulses,
peanuts, fish etc.
•These acids are the building block units of proteins. These
are the organic compounds which contain amino as well as
carboxyl functional groups known as amino acids.

55. Classification of Amino Acids
•Amino acids are classified as acidic, basic or
neutral depending upon the relative number of
amino and carboxyl groups in their molecule.
•Equal number of amino and carboxyl groups
makes it neutral;
•More number of amino than carboxyl groups
makes it basic
•More carboxyl groups as compared to amino
groups makes it acidic.

56. •The amino acids, which can be synthesised in
the body, are known as non- essential amino
acids.
•On the other hand, those which cannot be
•synthesised in the body and must be obtained
through diet, are known as essential amino
acids

57. Peptide bond
•A peptide bond is a covalent chemical bond,
which joins two amino acids by removing a
water molecule (H2O) from an amino group
(–NH2) of one amino acid and a carboxyl group
(–COOH) of the adjacent amino acid in a
polypeptide chain.

59. Isoelectric point
•The isoelectric point is the point at which the net charge of
the amino acid or protein is zero.
Or
The pH at which no net migration of the amino acid under
influence of an applied electric field
pH for neutral amino acid is slightly less than 7
pH for acidic amino acid is 3.0 – 5.4
pH for basic amino acid is 7.6 – 10.8

60. Zwitter ion
•In aqueous solution, the carboxyl group can
lose a proton and amino group can accept a
proton, giving rise to a dipolar ion known as
zwitter ion.

61. •Proteins can be classified into two types on
the basis of their molecular shape.
•a) Fibrous proteins
•b) Globular proteins

62. Fibrous proteins

•When the polypeptide chains run parallel and
are held together by hydrogen and disulphide
bonds, then fibre– like structure is formed.
Such proteins are generally insoluble in water.
Some common examples are
•keratin (present in hair, wool, silk)
• myosin (present in muscles), etc.

63. Globular proteins

•This structure results when the chains of
polypeptides coil around to give a spherical
shape.
•These are usually soluble in water.
•common examples
•Insulin
•albumins

64. Structure and shape of proteins
Four different levels are
• primary,
•secondary,
•tertiary
•quaternary,

65. Primary structure of proteins
•Proteins may have one or more polypeptide
chains.
•Each polypeptide in a protein has amino acids
linked with each other in a specific sequence
• it is this sequence of amino acids
•that is said to be the primary structure of that
protein.

66. Covalent, peptide bonds which connect the amino acids together maintain
the primary structure of a protein.

67. Secondary Structure of Protein
two types alpha and beta structure

68. beta-pleated sheet

69. Tertiary structure of proteins

70. Quaternary structure of proteins

71. Denaturation of proteins:

•The loss in the biological activity of a protein
due to the unfolding of globules and uncoiling
of helix is termed denaturation of protein.
• During denaturation, secondary and tertiary
structures vanish, but primary structures
remain intact.
•The coagulation of egg white on steaming is a
typical example of denaturation.

72. •Proteins can be denatured (physical and
biological changes), but there is no chemical
variation in the protein structure.
•Denaturation can arise due to various factors,
such as changes in temperature, pH, or
specific chemical agents.

73. •Proteins are formed primarily from ______
bonds.
a) glycosidic b) peptide
c) phosphodiester d) disulphide

74. •Proteins are _______
a) dipeptides
b) tripeptides
c) tetrapeptides
d) polypeptides

75. •Which of the following is not a fibrous
protein?
a) Keratin
b) Myosin
c) Collagen
d) Albumin

76. •The sequence in which amino acids are arranged in a
protein is called ______structure.
a) primary
b) secondary
c) fibrous
d) sheet

77. Enzymes
•Enzymes are biological catalysts which
catalyse chemical reactions in living
organisms.
•example, hydrolysis of maltose is catalysed by
maltase.
•The enzymes process best at an optimum
temperature range of 298 K to 313 K. Their
activity decreases with a decrease or increase
in temperature and stops at 273 K.

78. •Diseases caused by enzyme are
•PKU(phenylketone urea) mental diseases
•Albinism(white skin)
•Streptokinase(blood clot formation)

79. Vitamins
•These are the biomolecules which are not
produced by the body and hence, need to be
supplied in small amounts for necessary
biological functions.
•Vitamins are an essential dietary factor.
•A, B, C, D, E, & K vitamins are present in
various food forms.

80. Classification of vitamins
•classified into two categories:
•Water-soluble vitamins
•Fat-soluble vitamins

81. Water-soluble vitamins

•Water-soluble vitamins are vitamin B and C
complex etc.
•These vitamins need to be transferred to the
body from time to time because they are
readily excreted in urine and cannot be stored
(except vitamin B12) in our body.

82. Fat-soluble vitamins

•Vitamins which are soluble in fat and oils
•but insoluble in water are kept in this group.
These are vitamins A, D, E and K.
They are stored in liver and adipose (fat storing)
tissues.

83. •Particular vitamins are responsible for certain essential functions.
Vitamin A: Required to enable night vision in humans. Cells require
Vitamin A for the transfusion of light.
•Vitamin B: Necessary for creating serotonin, myelin, dopamine and
epinephrine. It also lowers cholesterol levels.
•Vitamin C: Increases the immune system and helps fatigued
muscles.
•Vitamin D: The formation of RNA needs Vitamin D. It also helps
bones absorb calcium to stay healthy and strong and reduces the
risk of fractures
•Vitamin E has antioxidant properties that help our bodies get rid of
free radicals and assist in the formation of red blood cells.
•Vitamin K: Essential in creating some crucial proteins, Various
important vitamins, their sources and their deficiency diseases.

85. Nucleic acids

•the particles in the nucleus of the biological
cell responsible for heredity are called
chromosomes which are made up of proteins
and other biomolecules called nucleic acids.
Nucleic acids are polymers which are present
in all human bodies.

86. •Nucleic acids play an essential role in the
development and reproduction of every life
form.
•Nucleic acid contains the elements carbon-
oxygen, nitrogen and phosphorus.
•They have nucleotides as their repeating units.

87. •Two types of nucleic acids:
•DNA (Deoxyribonucleic acid).
•RNA (Ribonucleic acid).

88. Deoxyribonucleic Acid (DNA)
•Chemically, DNA comprises a pentose sugar, phosphoric
acid and a few cyclic bases containing nitrogen.
•The sugar unit present in DNA molecules is β-D-2-
deoxyribose.
•The cyclic bases that have nitrogen-containing in them are
Adenine (A), guanine (G), thymine (T) and cytosine(C).
•These bases and their configuration in the molecules of
DNA play an essential role in storing information from one
generation to the next.
•DNA has a double-strand helical structure in which the
strands complement each other.

89. Ribonucleic Acid (RNA)
•The RNA molecule is also composed of
phosphoric acid, a pentose sugar and a few cyclic
bases containing nitrogen.
•RNA has β-D-ribose in it as the sugar unit.
•The heterocyclic bases available in RNA are
Adenine (A), guanine (G), cytosine(C) and uracil
(U).
•In RNA, the fourth base varies from that of DNA.
•The RNA commonly consists of a single strand
which sometimes folds back; that results in a
double helix structure.

90. Chemical composition of nucleic acids
•Nucleotides contain three chemical
components:
•A heterocyclic base.
•A five-carbon sugar moiety.
•A phosphate group.

91. •Nucleoside: A nucleoside unit is produced
when a nitrogen base is attached to a sugar
molecule.
•Base + sugar = nucleoside.

92. •Nucleotide: When a nitrogen base is attached
to a sugar molecule and phosphate, the unit
forms a nucleotide.
•Base+Sugar+phosphate → nucleotide.

93. the biological functions of nucleic
acids
•Nucleic acids are responsible for transmitting
inherent characteristics from parent to
offspring.
•DNA fingerprinting is a method that is used by
forensic experts to determine paternity. This
method is also used for the identification of
criminals. It has also played a significant role
in biological evolution and genetics studies.

94. Mutation
•A chemical process in a DNA molecule leads to
the synthesis of proteins with a changed
amino acid sequence. Radiation, viruses or
chemical agents cause these changes.
•Special enzymes replicate most changes in
DNA in the cell, but if there is a failure to
repair by the enzymes, then it can cause
mutation.

95. Hormones
•Hormones are chemical compounds which are
produced in ductless glands in the body.
Because of their function, hormones are also
termed chemical messengers.

96. •Hormones have various functions in the body.
They help to adjust the balance of biological
activities in the body.
•Testosterone is the primary sex hormone
developed in males and
•Progesterone is the primary sex hormone in
females.
•insulin in keeping the blood glucose level
within the narrow limit
•Thyroxine produced in the thyroid gland is an
iodinated derivative of amino acid tyrosine

97. •Which of the following statement is incorrect?
a) Vitamin deficiency causes diseases
b) Excess vitamin intake is harmful
c) Vitamins contain amino groups
d) Vitamins can be produced by plants

98. •Which of the following vitamins are soluble in
water?
a) A
b) C
c) D
d) E

99. •The condition of excess intake of vitamins is
called ________
a) denaturation
b) renaturation
c) avitaminoses
d) hypervitaminoses

100. •RNA on hydrolysis does not yield which of the
following?
a) Amino acid
b) Pentose sugar
c) Nitrogen base
d) Phosphoric acid

101. •Which of the following statement is incorrect?
a) Vitamin deficiency causes diseases
b) Excess vitamin intake is harmful
c) Vitamins contain amino groups
d) Vitamins can be produced by plants

102. •Which of the following vitamins are soluble in
water?
a) A
b) C
c) D
d) E

103. •The condition of excess intake of vitamins is
called ________
a) denaturation
b) renaturation
c) avitaminoses
d) hypervitaminoses

104. •RNA on hydrolysis does not yield which of the
following?
a) Amino acid
b) Pentose sugar
c) Nitrogen base
d) Phosphoric acid