What are Biomolecules?

Biomolecules are the essential organic molecules involved in the

maintenance and metabolic processes of living organisms. These non-living
molecules are the actual foot-soldiers of the battle of sustenance of life. They
range from small molecules such as primary and secondary metabolites and
hormones to large macromolecules like proteins, nucleic acids,
carbohydrates, lipids etc.

Carbohydrates
Carbohydrates are chemically defined as polyhydroxy aldehydes or ketones
or compounds which produce them on hydrolysis. They are called
carbohydrates as they comprise carbon, hydrogen and oxygen at their
chemical level. Carbohydrates are essential nutrients which include sugars,
fibers and starches. They are found in grains, vegetables, fruits and in milk
and other dairy products. They are the basic food groups which play an
important role in a healthy life. The food containing carbohydrates are
converted into glucose or blood sugar during the process of digestion by the
digestive system. Our body utilizes this sugar as a source of energy for the
cells, organs and tissues. The extra amount of energy or sugar is stored in
our muscles and liver for further requirement. The term ‘carbohydrate’ is
derived from a French term ‘hydrate de carbone’ meaning ‘hydrate of
carbon’. The general formula of this class of organic compounds is C n(H2O)n.

Classification of Carbohydrates
Although a number of classification schemes have been devised for
carbohydrates, they are usually divided into four major groups—
monosaccharides, disaccharides, oligosaccharides, and polysaccharides.

 Monosaccharides
Monosaccharides are any of the basic compounds that serve as the building
blocks of carbohydrates. Monosaccharides are polyhydroxy aldehydes or
ketones; that is, they are molecules with more than one hydroxyl group
(―OH), and a carbonyl group (C=O) either at the terminal carbon atom
(aldose) or at the second carbon atom (ketose). The carbonyl group
combines in aqueous solution with one hydroxyl group to form a cyclic
compound (hemi-acetal or hemi-ketal). Monosaccharides are classified by
the number of carbon atoms in the molecule; dioses have two, trioses three,
tetroses four, pentoses five, hexoses six, and heptoses seven. Most contain
five or six. The most-important pentoses include xylose, found combined as
xylan in woody materials; arabinose from coniferous trees; ribose, a
component of ribonucleic acids (RNA) and several vitamins; and deoxyribose,
a component of deoxyribonucleic acid (DNA). Among the most-important
aldohexoses are glucose, mannose, and galactose; fructose is a ketohexose.

 Disaccharides
Disaccharides are compounds composed of two molecules of
monosaccharides linked to each other. Disaccharides are crystalline water-
soluble compounds. The monosaccharides within them are linked by a
glycosidic bond (or glycosidic linkage), the position of which may be
designated α- or β- or a combination of the two (α-,β-). Glycosidic bonds are
cleaved by enzymes known as glycosidases. The three major disaccharides
are sucrose, lactose, and maltose.

 Oligosaccharides
Oligosaccharide are carbohydrate composed of three to six units of
monosaccharides. A large number of oligosaccharides have been prepared
by partially breaking down more complex carbohydrates (polysaccharides).
Most of the few naturally occurring oligosaccharides are found in plants.
Raffinose, a trisaccharide found in many plants, consists of melibiose
(galactose and glucose) and fructose. Another plant trisaccharide is
gentianose. Maltotriose, a trisaccharide of glucose, occurs in some plants
and in the blood of certain arthropods.
  Polysaccharides
Polysaccharides are composed of large number of sugar molecules; hence
they are referred to as starchy foods. They are also known as glycans.
Polysaccharides are digested and converted slowly compared to simpler
carbohydrates. They are abundantly found in lentils, beans, peanuts,
potatoes, peas, corn, whole-grain bread, cereals, etc. They are of two types:
 Homopolysaccharides: They are composed of only a single type of
sugar unit. Based on the function they perform, homopolysaccharides
are classified into two groups:
o Structural polysaccharides: They provide mechanical stability
to cells, organs, and organisms. Examples are chitin and
cellulose. Chitin is involved in the construction of a fungal cell
wall, while cellulose is an important constituent of the diet for
ruminants.
o Storage polysaccharides: They serve as carbohydrate stores
that release sugar monomers when required by the body.
Examples include starch, glycogen, and inulin. Starch stores
energy for plants. In animals, it is catalyzed by the enzyme
amylase (found in saliva) to fulfill the energy requirement.
Glycogen is a polysaccharide food reserve of animals, bacteria,
and fungi.
  Heteropolysaccharides: They contain two or more different types of
sugar units. It includes glycosaminoglycans like hyaluronic acid,
heparan sulfate, keratan sulfate, and murein. These polysaccharides
have diverse functions. For example, heparin is an anticoagulant
(prevents blood clotting, it’s also known as blood thinners), hyaluronic
acid is a shock absorber and lubricant, while peptidoglycans or mureins
are present in the bacterial cell wall.

Functions of Carbohydrates
Carbohydrates are known as one of the basic components of food, including
sugars, starch, and fibre which are abundantly found in grains, fruits and
milk products. The main function of carbohydrates is to provide energy and
food to the body and to the nervous system. It is also involved in fat
metabolism and prevents ketosis. Inhibits the breakdown of proteins for
energy as they are the primary source of energy.

Energy Homeostasis:
Sugar (in the form of glucose) is the main energy source for the body and the
only energy source the brain can utilize. Problems with carbohydrate
homeostasis can result in diabetes mellitus or hypoglycemia. An enzyme by
name amylase assists in the breakdown of starch into glucose, finally to
produce energy for metabolism.

Nucleotide Formation:
DNA and RNA are made of up nucleic acids, which consist of a sugar
(deoxyribose or ribose) bound to phosphate and a nitrogenous base.

Glycoprotein Formation:
Glycoproteins result from a carbohydrate attaching to a amino-acid or
polypeptide chain. Mucin (a component of mucus), hemoglobin A1c,
antibodies in the immune system, and clotting factors are examples.
Proteins
Proteins are another class of indispensable biomolecules, which make up
around 50% of the cellular dry weight. Proteins are the fundamental building
blocks of our body. They are large and complex macromolecules or bio-
molecules which perform a major role in the functioning and regulating of
our body cells, tissues and other organs in the human body. They are also
used in providing strength to our body in producing hormones, enzymes, and
other metabolic chemicals. They are also involved in functioning and
regulating of our body cells, tissues and organs. Proteins are polymers of
amino acids arranged in the form of polypeptide chains. These fundamental
amino acids sequences are specific and its arrangements are controlled by
the DNA. In general, they are two types of protein molecules: fibrous proteins
and globular proteins. Fibrous proteins are insoluble and elongated. Globular
proteins are soluble and compact. Fibrous and Globular proteins may
comprise up to four levels of protein structures: primary, secondary, tertiary
and quaternary structure.

o Primary Structure: It is a specific sequence of amino acids. The order

of amino acids bonded together is detected by information stored in
genes.
o Secondary Structure: It is a three-dimensional form of a local
segment of proteins. They are formed by hydrogen bonds between the
atoms along the backbone of the polypeptide chain.
o Tertiary Structure: It is determined by R-groups. It is a three-
dimensional shape of a protein. Many numbers of tertiary structure fold
to form Quaternary Structure.
o Quaternary Structure: It is the arrangement of multiple folded
protein subunits in a multi-subunit complex.

Protein synthesis takes place through a process called translation. This

process occurs in the cytoplasm. It involves the rendering of genetic codes.
Ribosomes of a cell help in translating genetic codes into a polypeptide
chain. These polypeptide chains become functioning proteins only after
undergoing certain modifications.

Functions of Proteins:

o Enzymes: Enzymes mostly carry out all numerous chemical reactions

which take place within a cell. They also help in regenerating and
creating DNA molecules and carry out complex processes.
o Hormones: Proteins are involved in the creation of various types of
hormones which help in balancing the components of the body. For
example, hormones like insulin, which helps in regulating blood sugar
and secretin. It is also involved in the digestion process and formation
of digestive juices.
o Antibody: Antibody also known as an immunoglobulin. It is a type of
protein which is majorly used by the immune system to repair and heal
the body from foreign bacteria. They often work together with other
immune cells to identify and separate the antigens from increasing
until the white blood cells destroy them completely.
o Energy: Proteins are the major source of energy that helps in the
movements of our body. It is important to have the right amount of
protein in order to convert it into energy. Protein, when consumed in
excess amounts, gets used to create fat and becomes part of the fat
cells.
Nucleic Acids
Nucleic acids refer to the genetic material found in the cell that carries all
the hereditary information from parents to progeny. There are two types of
nucleic acids namely, deoxyribonucleic acid (DNA) and ribonucleic acid
(RNA). These molecules are composed of long strands of nucleotides held
together by covalent bonds. The monomeric unit of nucleic acids is known as
nucleotide and is composed of a nitrogenous base, pentose sugar, and
phosphate. The nucleotides are linked by a 3’ and 5’ phosphodiester bond.
The nitrogen base attached to the pentose sugar makes the nucleotide
distinct. There are 4 major nitrogenous bases found in DNA: adenine,
guanine, cytosine, and thymine. In RNA, thymine is replaced by uracil. The
DNA structure is described as a double-helix or double-helical structure
which is formed by hydrogen bonding between the bases of two antiparallel
polynucleotide chains. Overall, the DNA structure looks similar to a twisted
ladder. In eukaryotes, DNA is found in the nucleus, a specialized, membrane-
bound vault in the cell, as well as in certain other types of organelles (such
as mitochondria and chloroplasts). And DNA is typically broken up into a
number of very long, linear pieces called chromosomes. While in
prokaryotes, the DNA is not enclosed in a membranous envelope, although
it's located in a specialized cell region called the nucleoid and chromosomes
are much smaller and often circular (ring-shaped). A chromosome may
contain tens of thousands of genes, each providing instructions on how to
produce protein products, meaning that they specify the sequence of amino
acids used to build a particular protein. Before this information can be used
for protein synthesis, however, an RNA copy (transcript) of the gene must
first be made. This type of RNA is called a messenger RNA (mRNA), as it
serves as a messenger between DNA and the ribosomes, molecular
machines that read mRNA sequences and use them to build proteins. This
progression from DNA to RNA to protein is called the “central dogma” of
molecular biology. Importantly, not all genes encode protein products. For
instance, some genes specify ribosomal RNAs (rRNAs), which serve as
structural components of ribosomes, or transfer RNAs (tRNAs), cloverleaf-
shaped RNA molecules that bring amino acids to the ribosome for protein
synthesis.
Lipids
Lipids are organic substances that are insoluble in water, soluble in organic
solvents, are related to fatty acids and are utilized by the living cell. Lipids
can be classified as saponifiable (comprising of one or more ester groups,
enabling it to undergo hydrolysis in the presence of a base, acid, or
enzymes) or nonsaponifiable (cannot be disintegrated into smaller molecules
through hydrolysis). The four main groups of lipids include:
 Fatty acids (saturated and unsaturated)
 Glycerides (glycerol-containing lipids)
 Nonglyceride lipids (sphingolipids, steroids, waxes)
 Complex lipids (lipoproteins, glycolipids)

Fatty Acids
The carboxylic acid products found in the saponifiable lipids are referred to
as fatty acids. The fatty acids are long, unbranched monocarboxylic acids
containing 10 to 22 carbon atoms. They typically have an even number of
carbon atoms due to their biosynthetic pathway. The Fatty acids can be
classified into families based on chain length and on the number of C=C
double bonds present. Saturated fatty acids contain no C=C double bonds.
(Saturated = bonded to the maximum number of hydrogens; will not accept
any more hydrogen) Unsaturated fatty acids contain C=C double bonds.
(These will accept more hydrogen.) Free fatty acids are rare in the cell; free
fatty acids are somewhat toxic to cells. Fatty acids are typically found as
components of larger lipid molecules. Free fatty acids are transported
through the blood bound to serum albumin. They provide insulation to the
body and are an efficient way to store energy for longer periods.

Glycerides
Glycerides are lipid esters of the glycerol molecule and fatty acids. The
primary function of the glycerides is energy storage. Glycerides can be
subdivided into two categories. The first group, the neutral glycerides are
nonionic and nonpolar. The second group, the phosphoglycerides contain a
polar region, the phosphoryl group. Both of these two types of glycerides can
be seen as possessing a three carbon "backbone" of the glycerol molecule.
Esterification of glycerol with a fatty acid produces a neutral glyceride.
Esterification may occur at one, two or all three positions producing
monoglycerides (monoacylglycerols), diglycerides (diacylglycerols), or
triglycerides (triacylglycerols). The most prevalent and most important are
the triglycerides. Phosphoglycerides or phospholipids are major components
of the plasma membrane. Like fats, they are typically composed of fatty acid
chains attached to a backbone of glycerol. Instead having three fatty acid
tails, however, phospholipids generally have just two, and the third carbon of
the glycerol backbone is occupied by a modified phosphate group. Different
phospholipids have different modifiers on the phosphate group, with choline
(a nitrogen-containing compound) and serine (an amino acid) being common
examples. Different modifiers give phospholipids different properties and
roles in a cell.

Nonglyceride Lipids

 Sphingolipids though not derived from glycerol, can still be visualized

as a three-carbon backbone molecule just as the triglycerides or the
phospholipids. Instead of the three-carbon backbone of glycerol, the
three-carbon backbone is sphingosine. Sphingosine is a nitrogen-
containing alcohol (amino alcohol). They also are amphipathic, having
a polar head group and two nonpolar fatty acid tails. They also are
structural components of cellular membranes.
 Steroids are lipids with the principal function of signaling chemical
biological activities. Steroids are members of a large, diverse collection
of lipids called the isoprenoids. All of these compounds are built from
one or more five-carbon units called isoprene.
  Waxes are simple lipids which are esters of a long-chain alcohol and a
fatty acid. The alcohol may contain from 12-32 carbon atoms. Waxes
are found in nature as coatings on leaves and stems. The wax prevents
the plant from losing excessive amounts of water.

Complex Lipids

These important lipids are widely distributed in plants, bacteria and animals.
They are the major constituents of cell membranes but are found also in
circulating fluids. They contain frequently three or more chemical identities
(i.e. glycerol, fatty acids and sugar, one long chain base, one fatty acid, one
phosphate group and one nucleoside group…) and have polar properties.
Some contain only two components but including a sugar moiety.

They can be classified into four main groups:

 Phospholipids: Lipids with a phosphate residue, one glycerol, or an

aminoalcohol or a fatty alcohol, and with one or two fatty chains
(exceptionally one inositol group, two phosphates or four fatty chains):
 Glycolipids: Lipids containing a glycosidic moiety with a glycerol or an
aminoalcohol and with fatty chain(s) (sometimes with one or more
phosphate groups):
 Lipoamino Acids: Lipids without phosphate group and containing one
amino acid linked to long-chain alcohol and acids:
 Nucleolipids: Lipids containing a nucleobase, or a nucleoside, or a
nucleotide or an oligonucleotide: