• Chemicals or molecules present in the living organisms are known
• The sum total of different types of biomolecules, compounds and
ions present in a cell is called as cellular pool
• Biomolecules are compounds of carbon. Hence the chemistry of
living organisms is organized around carbon
• Carbon is the most versatile and the most predominant element
4. • Cells and their organelles are made up of smaller building blocks
• Macromolecules are actually made up of even smaller subunits.
Each subunit of a macromolecule is called a monomer.
• The macromolecules themselves are called polymers, because
they are made up of many of these subunits.
• Macromolecules are formed when monomers are linked to form
longer chains called polymers.
• A macromolecule is a very large molecule commonly created by
polymerization of smaller subunits.
• ‘A macromolecule is a very large molecule commonly created
by polymerization of smaller subunits’.
• In biochemistry, the term is applied to the four conventional
biopolymers (nucleic acids, proteins, carbohydrates, and lipids).
• ‘A macromolecule is a molecule with a very large number of
atoms. Macromolecules typically have more than 100 component
Small sized, low mol
wt Between 18 and
800 daltons Found in
the acidsoluble pool
Sugars Amino acids
Large sized,high mol
wt Above 1000
daltons Found in the
• There are four macromolecules essential to living matter
containing C, H, O, N and sometimes S.
• Nucleic Acids
11. • Carbohydrates can be represented by the chemical formula
where n is the number of carbons in the molecule.
• the ratio of carbon to hydrogen to oxygen is 1:2:1 in carbohydrate
• This formula also explains the origin of the term “carbohydrate”:
the components are carbon (“carbo”) and the components of
water (hence, “hydrate”).
• Carbohydrates are classified into three subtypes:
monosaccharides, disaccharides, and polysaccharides.
12. • The monomers of carbohydrates are the monosaccharide units
that are the basic building blocks of all sugars and starches.
• The polymers of carbohydrates are disaccharides and
polysaccharides that consist of two or more monomers
• Monosaccharides (mono- = “one”; sacchar- = “sweet”) are
simple sugars, the most common of which is glucose.
• In monosaccharides, the number of carbons usually ranges
from 3 to 7.
• Most monosaccharide names end with the suffix “-ose.”
• If the sugar has an aldehyde group (the functional group with
the structure R-CHO), it is known as an aldose, and
• if it has a ketone group (the functional group with the structure
RC(=O)R’), it is known as a ketose.
16. • Depending on the number of carbons in the sugar, they also may
be known as trioses (three carbons), pentoses (five carbons), and
or hexoses (six carbons).
• Disaccharides (di- = “two”) form when two monosaccharides
undergo a dehydration reaction (also known as a condensation
reaction or dehydration synthesis).
• During this process, the hydroxyl group of one monosaccharide
combines with the hydrogen of another monosaccharide,
releasing a molecule of water and forming a covalent bond. A
covalent bond formed between a carbohydrate molecule and
another molecule (in this case, between two monosaccharides) is
known as a glycosidic bond or glycosidic linkage.
• Oligosaccharides consist of short chains of monosaccharide
units (usually 3–9 monosaccharides), covalently linked to form
• They are named trioses, tetroses, etc., denoting the number of
carbons in their molecule.
• Oligosaccharides are distributed widely in plants, and when
digested yield their constituent monosaccharides.
• Eg: raffinose, stachyose, and verbascose
• A long chain of monosaccharides linked by glycosidic bonds is
known as a polysaccharide (poly- = “many”).
• The chain may be branched or unbranched, and it may contain
different types of monosaccharides.
• Polysaccharides contain more than 10 monosaccharide units
• Starch, glycogen, cellulose, chitin, and peptidoglycans are
primary examples of polysaccharides.
• Proteins are one of the most abundant organic molecules in living
systems and have the most diverse range of functions of all
• Each cell in a living system may contain thousands of proteins,
each with a unique function and structure.
• All proteins are polymers of amino acids arranged in a linear
26. Amino acids
• Amino acids are the monomers
that make up proteins.
• Each amino acid has the same
fundamental structure, which
consists of a central carbon atom,
also known as the alpha carbon,
bonded to an amino group (NH2),
a carboxyl group (COOH), a
hydrogen atom, and an R group.
27. • The side group of an amino acid is a substituent group.
• It determines the nature and chemical properties of the amino
acid and influences its solubility in water.
• Amino acids differ from each other only in the chemical nature of
their side groups,
• the side groups of different kinds of amino acids vary in size,
structure and electric charge
• So, there would be as many kinds of amino acids as there are
different kinds of side groups
28. • In complexity, the side groups range from a single hydrogen atom
(as in glycine) to a methyl (CH3) group (e.g.. Alanine), or to a
complex chain called side chain or R-group. The R-group may be
aromatic (e.g, in tyrosine, phenylalanine), aliphatic (e.g., in
alanine, arginine, lysine, leucine, serine, valine, methionine, etc.),
or heterocyclic (e.g., in tryptophan, histidine, proline). Some
amino acids contain S. P.
• Or additional carbon in their side chains. Amino acids, such as
aspartic acid, glutamic acid, cysteine, tyrosine, histidine and
arginine, possess R-groups having ionizable substituents
29. • The sequence and the number of amino acids ultimately
determine the protein’s shape, size, and function.
• The amino acids are attached by a covalent bond, known as a
peptide bond, which is formed by a dehydration reaction.
• The carboxyl group (COOH) of one amino acid and the amino
group of the incoming amino acid combine, releasing a molecule
32. • The lipids are a heterogeneous group of compounds related to fatty
acids and include fats, oils, waxes and other related substances.
• These are oily or greasy organic substances, relatively insoluble in
water and considerably soluble in organic solvents like ether,
chloroform and benzene.
33. • Molecular components
• Lipids are formed of C. H and O, and occasionally N and P also.
• Cellular lipids are primarily esters of fatty acids and alcohols.
Fatty acids, in general, are long-chain aliphatic organic acids.
• The commonest alcohol in both plant and animal cells is glycerol.
But, in some plant lipids, it is replaced by cholesterol.
35. Fatty acids
• Fatty acids are aliphatic hydrocarbonchains, with a carboxyl group at
one end. In other words,they are long, straight-chain monocarboxylic
• A fatty acid molecule consists of a long, non-polar, acyclic (aliphatic)
and unbranched hydrocarbonchain, linked with a polar and ionizable
carboxyl (-COOH)group at one end
• Thus,fatty acids are amphipathicmolecules, since they contain both
polar and non-polar groups.
• The carboxyl group formsthe “head”of the molecule, and the
hydrocarbonchain formsits “tail”.
• The hydrocarbon(fatty acid) chain has a back bone of carbonatoms to
which hydrogenatoms remain attached.
36. • There are 2 groups of fatty acids
1. Saturated fatty acid
2. Unsaturated fatty acid
• In saturated fatty acids, the maximum possible number of
hydrogen atoms remain attached to the carbon back bone. So, in
them, adjacent carbon atoms are linked through single bonds.
• Solid at room temperature
• Mainly animal fat
• Eg: acetic acid palmitic acid
37. • The hydrocarbonchains of unsaturatedfatty acids have one or more
double bonds that bend the chain, making close packing less possible.
• Liquid at room temperature
• Eg: Most plant fats ( often Called oil)
• Linoleic acid, Linolenic acid
• Glycerol is a straight chain trihydroxy alcohol, which can readily
combine with weak acids.
• A glycerol molecule has three linkage sites for esterifying three
fatty acid molecules.
• The linkage occurs between the acidic carboxyl (-COOH) group of
the fatty acid molecule and the alcoholic hydroxyl (-OH) group of
the glycerol molecule, with the elimination of one molecule of
39. • A hydrogen atom from the –OH group breaks away and combines
with the hydroxyl radical of the-COOH group and forms one
molecule of H2O.
• Consequently, adjacent carbon atoms link together through an
oxygen atom. This type of linkage between an acidic group and an
alcoholic group is known as ester linkage.
• The products of the ester linkage between fatty acids and glycerol
are known as glycerides.
• They are neutral fats.
40. • Lipids have a molecular weight less than 1 kDa. They are a part of
the membranes in a cell. When the cell structure is disrupted,
these molecules form vescicles and become part of the acid
insoluble pool. Hence they are not strictly biomacromolecules
42. Nucleic acids
• Nucleic acids are biopolymers, macromolecules, essential to all
known forms of life.
• A major function of nucleic acids involves the storage and
expression of genomic information.
• They are composed of nucleotides, which are the monomer
a 5-carbon sugar,
a phosphate group
a nitrogenous base.
43. • The two main classes of nucleic acids are,
• deoxyribonucleic acid (DNA) and
• Ribonucleic acid (RNA).
• If the sugar is ribose, the polymer is RNA; if the sugar is
deoxyribose, a version of ribose, the polymer is DNA.
46. • The nitrogenous bases of the two separate polynucleotide strands
are bound together, according to base pairing rules (A with T, and
C with G), with hydrogen bonds to make double-stranded DNA.
• There are 2 hydrogen bond between A and T and 3 hydrogen bond
between G and C.
47. A single nucleic acid strand is a phosphate-pentose polymer with
purine and pyrimidine bases as side group.
DNA molecules consist of two biopolymer strands coiled around
each other to form a double helix. The two DNA strands are termed
polynucleotides since they are composed of simpler monomer
units called nucleotides.
The nucleotides are joined to one another in a chain by covalent
bonds between the sugar of one nucleotide and the phosphate of
the next, resulting in an alternating sugar-phosphate backbone
50. • The biological molecules are divided into four major categories;
carbohydrates, lipids, proteins, and nucleic acids.
• All these biological molecules are formed as a result of chemical
associations or linkages between different atoms.
• These bonds not only form the biological molecule but are also
responsible for the maintenance of their complex structures.
51. • The chemical bonds in case of biological molecules can be
divided into two categories;
1. Primary Bonds
2. Secondary Bonds
52. Primary bonds
• These are the covalent bonds formed as a result of electron
sharing among two or more atoms.
• Primary bonds are the permanent attractions that are developed
among the atoms by the sharing of electrons.
• The formation of a primary bond either consumes or releases
energy and the same energy is needed to break the primary bond.
• Primary bonds usually form the primary structure of the biological
molecules except the disulfide linkage that serves to maintain the
secondary or tertiary structures.
53. • Various type of primary bonds
1. Glycosidic bond
2. Peptide bond
3. Ester bond
4. Phosphodiester bond
54. Glycosidic bond
• It is a primary bond or a covalent bond that serves to connect
carbohydrates to other groups or molecules.
• The partner or combining molecule may be carbohydrate or non-
carbohydrate in nature.
• This bond is formed as a result of a reaction between the
carbonyl group of a carbohydrate and a hydroxyl group of
some other compound.
• The carbonyl group of carbohydrate may be a part of an
aldehydic group or a ketonic group. A molecule of water is
released in this process, making it an irreversible reaction.
• Glycosidic bond undergoes degradation in a process called
glycolysis. It is a hydrolytic process in which a water molecule is
used to break the glycosidic bond and release the carbohydrate
and other residues.
• Enzymes required to break different types of glycosidic bonds are
present in different animals.
57. Peptide bond
• It is the second most abundant bond found in biological
molecules. A peptide bond is the one that links amino acids to
form polypeptide chains.
• It is a covalent bond formed as a result of a chemical reaction
between the amino group of one amino acid and the carboxylic
group of another amino acid.
59. • As mentioned above, it is formed when the amino group and the
carboxylic groups of amino acids react and release a water
• It is only formed when both the carboxylic group and the amino
group are non-side chain groups.
• It means that in order to form a peptide bond, both the groups
much be attached to the alpha carbon and must not be a
component of the side chains of amino acids.
60. • In the process of making a peptide bond, the carboxylic group
loses hydrogen and oxygen atoms while the amino group only
loses its hydrogen.
• The resultant compound is called a dipeptide. This dipeptide can
also form additional peptide bonds because of the presence of
free amino group and carboxylic group at its N-terminal and C-
• Peptide bonds are broken down during the process of protein
degradation. It is also a hydrolytic process as a water molecule is
utilized to break the bond between two amino acids.
• In living organisms, the hydrolysis of the peptide bond is catalyzed
by enzymes during the digestion of proteins in GIT as well as the
normal turnover of proteins within the cell.
62. Ester bond
• It is a covalent bond that is essential in various types of lipids.
• An ester bond or ester linkage is formed between an acid and an
• An ester bond is formed when a molecule having the carboxylic
group reacts with another molecule having a hydroxyl group.
• The carboxylic group loses its hydrogen and oxygen while the
alcohol loses hydrogen of its hydroxyl group.
• As a result, a water molecule is released, and the two carbons are
linked via an oxygen bridge forming a –COC- linkage.
• Eg: The bonds between the glycerol and the fatty acids in a
• The ester linkage is a very high-energy bond releasing a
tremendous amount of energy upon hydrolysis.
• Like the rest of the bonds discussed earlier, it is also broken down
by incorporating a water molecule.
• The hydrolysis of the ester linkage yields 9 Kcal/g energy.
66. Phosphodiester bond
• It is the primary covalent bond that joins different nucleotides in a
polynucleotide or nucleic acids. It is also a type of ester bond but
involves two ester linkages.
Example : Phosphodiester bonds are used to attach nucleotides in
DNA and RNA. They are also present in dinucleotides like NAD and
68. • Phosphodiester bonds are formed when hydroxyl groups of
phosphate react with the hydroxyl group of the sugar. Water is
eliminated as the result of the reaction.
• Phosphodiester bonds maintain the structure of DNA and RNA
• The degradation of phosphodiester bonds also requires the use of
a water molecule and is thus a hydrolytic process. In living
organisms, the degradation of the phosphodiester bond is
catalyzed by specific enzymes called nucleases. They are of two
1. Exonucleases, they break the phosphodiester bond beginning
from one end of the chain.
2. Endonucleases, they can break the phosphodiester bond
even from within the chain of nucleotides.
70. Secondary bonds
• These bonds are the electrostatic attractions that are developed
among the atoms.
• The secondary bonds in biological molecules are the temporary
forces of attractions that are developed when certain atoms or
groups come close together.
• These bonds are mainly involved in maintaining the secondary,
tertiary or other higher structures of biological molecules.
• They are most important in proteins and nucleic acids.
71. • Various types of secondary bonds
1. Hydrogen bond
2. Hydrophobic interaction
3. Disulfide bond
4. Ionic bond
72. 1. Hydrogen bond
• It is the most important secondary bond in biological molecules.
• Hydrogen bond is the strongest secondary bond having strength
almost equal to that of covalent bonds.
• Hydrogen bonding is an important component of the three major
macromolecules in biochemistry such as proteins, nucleic acids,
• Hydrogen bond is formed as between a hydrogen atom and a
highly electronegative atom like oxygen or nitrogen.
• When a hydrogen atom comes within the electron affinity of a
highly electronegative atom like oxygen or nitrogen.
75. 2. Hydrophobic interactions
• These are the interactions among the non-polar molecules. Such
molecules cannot dissolve in water.
• However, they tend to clump together away from the polar or
• This clumping of hydrophobic molecules is called hydrophobic
• Hydrophobic interactions are important in maintaining the tertiary
and quaternary structure of proteins.
• They are also involved in protein folding.
77. 3. Disulfide bond
• Although it is a covalent bond, it is discussed under the heading of
secondary bonds because it is involved in maintaining the higher
structures of biological molecules.
• A disulfide bond is formed between the thiol groups present in the
side chains of two cysteine residues to form one cystine residue.
This bond brings the two cysteine residues together that have
been kept apart by the intervening amino acids.
78. • This bond is involved in stabilizing the tertiary structure of proteins
and guiding the protein folding.
79. 4. Ionic bond
• These are the secondary forces of attractions formed between the
• The acidic and basic groups in the side chains of amino acids
either have a positive or negative charge at the physiologic pH.
• Together they form strong attractions in the tertiary structure of
• They are also involved in the folding of proteins.