Biomolecules are macromolecular or polymeric molecule, consisting of
smaller monomeric units or the monomeric unit itself that are produced by
different in vivo processes or consumed by living organisms for different
types of metabolic process.
• Monomer: Smaller molecules that are used
to construct polymer or macromolecule.
Example: Glucose, amino acids etc.
• Polymeric structure: When one or two
monomeric units are arranged in a particular
pattern to form a large molecule, then it is a
polymeric structure.
Example: Starch and cellulose both are
polymer of glucose.
• Macromolecular structure: When a good
number of varieties of monomeric units are
arranged randomly in any possible number and
combination, without any repeating unit, then
it is called a macromolecular structure.
Example: Proteins are macromolecules
consisting of varieties of amino acids, without
a repeat unit.
Macromolecular structure of DNA
Carbohydrates
Carbohydrates are poly-hydroxy aldehydes or ketones or larger molecules derived from them. The first
kind being the monomeric carbohydrates and second kind are the oligomer or polymer.
Classification of Carbohydrates
Carbohydrates
Sugars Polysaccharides
Homo-Polysaccharides
Monosaccharides Oligosaccharides Example: Starch etc.
Example: Glucose,
Fructose, Galactose etc. Hetero-Polysaccharides
Example: Heparin etc.
Disaccharides Trisaccharides Tetrasaccharides
Example: Sucrose, Example: Gentianose, Example: Stachyose
Maltose, Lactose etc Raffinose etc. etc.
Carbohydrates have the general molecular formula Cn (H2O)m.
Sugars
Monosaccharides: Glucose, Fructose, Galactose, Mannose = C6H12O6 = C6 (H2O)6. n=m
Disaccharides: Sucrose, Lactose, Maltose = C12H22O11 = C12 (H2O)11 n≠m
Glucose (C6H12O6) + Fructose (C6H12O6) = Sucrose (C12H22O11) + Water (H2O)
Glucose (C6H12O6) + Glucose (C6H12O6) = Maltose (C12H22O11) + Water (H2O)
Glucose (C6H12O6) + Galactose (C6H12O6) = Lactose (C12H22O11) + Water (H2O)
Trisaccharides: Gentianose, Raffinose, Melezitose = C18H32O16 = C18 (H2O)16 n≠m
Glucose (C6H12O6) + Glucose (C6H12O6) + Fructose (C6H12O6) = Gentianose (C18H32O16) + Water (2H2O)
Glucose (C6H12O6) + Fructose (C6H12O6) + Glucose (C6H12O6) = Meleziatose (C18H32O16) + Water (2H2O)
Glucose (C6H12O6) + Fructose (C6H12O6) + Galactose (C6H12O6) = Raffinose (C18H32O16) + Water (2H2O)
Tetrasaccharides: Stachyose = C24H42O21 = C24(H2O)21 n≠m
Glucose (C6H12O6) + Fructose (C6H12O6) + Galactose (C6H12O6) + Galactose (C6H12O6) = Stachyose
(C24H42O21) + Water (3H2O)
Polysaccharides
Glycogen is the polymer of glucose when 10-14 units
of glucose combined in linear fashion. Glucose is
stored in human body in form of glycogen.
Cellulose is a polysaccharide consisting of a linear
chain of several hundred to many thousands of
β(1→4) linked D-glucose units. It is found in cotton
fiber, wood, hey, grass and primary cell walls of
green plants. It can be digested by bovine due to
presence of cellulase enzyme in their digestive
system. Cellulase hydrolyze cellulose into glucose.
Starch is a mixture of two polysaccharide, amylose
and amylopectin; both being the polymer of
Glucose. Starch is found in staple foods like
potatoes, wheat, maize (corn), rice, and cassava.
Starch is digested by human as follows:
Nucleic Acid
Nucleic acids are the biological macromolecules or small biomolecules that carries and contains the genetic information. They
are essential to all known forms of life. The nucleic acid is the of two types:
DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid).
The monomeric units of nucleic acids are called
Nucleotides.
Each nucleotide consists of following three sub-units:
1. A heterocyclic base, called Nucleic acid base:
purine or pyrimidine
There are two purine bases, Adenine and
Guanine Name of nucleotides and nucleosides
And three pyrimidine bases, Cytosine, Thymine
and Uracil
1. A pentose sugar: D-Ribose or 2-Deoxy-D-ribose
2. Phosphate Ion (PO4 3-)
Without the phosphate sub-unit, the monomeric
residual units are called Nucleosides
Structure of
DNA
DNA is a double-stranded helix, which
consists of two polynucleotide strands.
Polynucleotide strands of DNA consist of
three major components:
• Nucleic acid Base: Purine bases-
Adenine and Guanine; Pyrimidine
base: Cytosine and Thymine
• Pentose sugar: 2-Deoxy-D-ribose
• Phosphate ion: PO43-
Watson and Crick model
➢ According to the Watson and Crick model, the DNA is a double-stranded helix (twisted ladder-
like look), which consists of two polynucleotide strands, run in the antiparallel direction, i.e. one in 5’-3’
and other in 3’-5’ direction.
➢ The diameter of ds-stranded DNA helix is 20Å and the distance between the two nucleotides or
internuclear distance is 3.4Å.
➢ Turning of DNA causes a formation of wide indentations, i.e. “Major groove”. The distance between the
two strands forms a narrow indentation, i.e. “Minor groove”.
➢ Polynucleotide strands of DNA consist of three major components, namely nitrogenous
bases, deoxyribose sugar and a phosphate group.
➢ The backbone of DNA consists of the sugar-phosphate backbone.
➢ Adenine complementarily pairs with thymine through two hydrogen bonds, whereas guanine
complementarily pairs with cytosine by means of three hydrogen bonds.
➢ Therefore, the bonding between sugar and phosphates, i.e. phosphodiester bond and the bonding
between nitrogenous bases, i.e. hydrogen bond contributes to the “DNA Stability”.
Chargaff's rule
According to Chargaff's rule, the
amount of adenine (A) is equal to the
amount of thymine (T) and similarly,
the amount of cytosine (C) is equal to
the amount of guanine (G).
Hence, A = T and C = G.
So, the total amount of purines is
equal to the total amount of
pyrimidines.
Purines = Pyrimidines.
A+G=C+T
Structure of RNA
➢ A RNA molecule consists of monomeric units called
nucleotides which have following three sub-units
• Nucleic acid Base: Purine bases- Adenine (A) and
Guanine ( G); Pyrimidine base: Cytosine (C) and Uracil
(U).
• Pentose sugar: D-Ribose
• Phosphate ion: PO43-
➢ The nucleotides are connected by the phosphate
linkage; thus, a sugar-phosphate backbone is formed.
➢ Unlike the DNA, RNA has a single stranded structure,
generally expressed from 5ꞌ to 3ꞌ direction.
➢ However, the single strand can be coiled in such a way that
self assembly by complementary base pairing can be
observed in some cases.
➢ Two separate strand can be involved in base pairing and
form hairpin structure.
Adenine (A), Guanine(G) , Cytosine (C) and Uracil (U)
Different Types of RNA:
RNA Full Name Origin Function
mRNA Messenger RNA Nucleus Carries genetic information
(Codon).
tRNA Transfer RNA Cytoplasm Carries anticodon as the binding
site of amino acids and involved in
protein synthesis.
rRNA Ribosomal RNA Ribosome of the Directs the translation of mRNA
endoplasmic reticulum into protein
Codon and Anticodon
Lipids or Fats
Lipids are hydrophobic substances, soluble in oil. They are the esters of fatty acid and glycerol.
Types of Lipids or Fats
Depending on the esterification there are three types of lipids
Depending on the nature of fatty acid residue there are different types of lipids or fats
Phospholipids
The structure of the phospholipid molecule generally consists of two hydrophobic fatty acid
"tails" and a hydrophilic "head" consisting of a phosphate group. The two components are
usually joined together by a glycerol molecule. The fatty acid chains may be saturated or
unsaturated or both. They occur naturally in all living organisms as the major components
of cell membranes.
Glycolipids:
Glycolipids are lipids with a carbohydrate attached by a glycosidic bond. Usually a monosaccharide
molecule is connected to a glycerol molecule by glycosidic linkage. The lipid as a whole has a polar head
and a non-polar tail. The glycolipid bilayer of the cell membrane consists of two layers of lipids, with the
inner and outer surfaces of the membrane made up of the polar head groups, and the inner part of the
membrane made up of the non-polar fatty acid tails.
Function of Lipids
➢ Chemical messengers
➢ Storage and provision of
energy
➢ Cell membrane formation
➢ The "fat-soluble" vitamins
(A, D, E and K) are essential
nutrients with numerous
functions.
