Main articles: Lipid, Glycerol, and Fatty acid
Structures of some common lipids. At the top are cholesterol and oleic
palmitoylchains attached to a glycerol backbone. At the bottom is the
for relatively water-insoluble or nonpolar compounds of biological origin, including
waxes, fatty acids, fatty-acid derived phospho lipids, sphingolipids, glycolipids, and
terpenoids (e.g., retinoids and steroids). Some lipids are linear aliphatic molecules,
while others have ring structures. Some are aromatic, while others are not. Some are
flexible, while others are rigid.
Lipids are usually made from one molecule of glycerol combined with other
glycerol and three fatty acids. Fatty acids are considered the monomer in that case,
and may be saturated (no double bonds in the carbon chain) or unsaturated (one or
more double bonds in the carbon chain).
Most lipids have some polar character in addition to being largely nonpolar. In
meaning that it does not interact well with polar solvents like water. Another part of
their structure is polar or hydrophilic ("water-loving") and will tend to associate with
polar solvents like water. This makes them amphiphilic molecules (having both
hydrophobic and hydrophilic portions). In the case of cholesterol, the polar group is a
mere -OH (hydroxyl or alcohol). In the case of phospholipids, the polar groups are
considerably larger and more polar, as described below.
Lipids are an integral part of our daily diet. Most oils and milk products that we
use for cooking and eating like butter, cheese, ghee etc., are composed of fats.
Vegetable oils are rich in variouspolyunsaturated fatty acids (PUFA). Lipid-
containing foods undergo digestion within the body and are broken into fatty acids
and glycerol, which are the final degradation products of fats and lipids. Lipids,
especially phospholipids, are also used in various pharmaceutical products, either as
co-solubilisers (e.g., in parenteral infusions) or else as drug carrier components (e.g.,
in a liposome ortransfersome).
Main articles: Protein and Amino acid
The general structure of an
the carboxyl group on the right.
Generic amino acids (1) in neutral form, (2) as they exist physiologically, and
Proteins are very large molecules – macro-biopolymers – made from
monomers called amino acids. An amino acid consists of a carbon atom bound to four
groups. One is an amino group, —NH
, and one is a carboxylic acid group, —COOH
under physiologic conditions). The third
for each amino acid. There are 20 standard amino acids, each containing a carboxyl
group, an amino group, and a side-chain (known as an "R" group). The "R" group is
what makes each amino acid different, and the properties of the side-chains greatly
influence the overall three-dimensional conformation of a protein. Some amino acids
have functions by themselves or in a modified form; for instance, glutamate functions
as an important neurotransmitter. Amino acids can be joined via a peptide bond. In
this dehydration synthesis, a water molecule is removed and the peptide bond
connects the nitrogen of one amino acid's amino group to the carbon of the other's
carboxylic acid group. The resulting molecule is called a dipeptide, and short
stretches of amino acids (usually, fewer than thirty) are called peptides or
polypeptides. Longer stretches merit the title proteins. As an example, the important
blood serum protein albumin contains 585 amino acid residues.
A schematic ofhemoglobin. The red and blue ribbons represent the protein
Some proteins perform largely structural roles. For instance, movements of the
proteins actin and myosinultimately are responsible for the contraction of skeletal
muscle. One property many proteins have is that they specifically bind to a certain
molecule or class of molecules—they may be extremely selective in what they
bind.Antibodies are an example of proteins that attach to one specific type of
molecule. In fact, the enzyme-linked immunosorbent assay (ELISA), which uses
antibodies, is one of the most sensitive tests modern medicine uses to detect various
biomolecules. Probably the most important proteins, however, are the enzymes.
Virtually every reaction in a living cell requires an enzyme to lower the activation
energy of the reaction. These molecules recognize specific reactant molecules called
substrates; they then catalyze the reaction between them. By lowering the activation
energy, the enzyme speeds up that reaction by a rate of 10
or more; a reaction that
a second with an enzyme. The enzyme itself is not used up in the process, and is free
to catalyze the same reaction with a new set of substrates. Using various modifiers,
the activity of the enzyme can be regulated, enabling control of the biochemistry of
the cell as a whole.
The structure of proteins is traditionally described in a hierarchy of four levels.
The primary structure of a protein simply consists of its linear sequence of amino
acids; for instance, "alanine-glycine-tryptophan-serine-glutamate-asparagine-glycine-
lysine-…". Secondary structure is concerned with local morphology (morphology
being the study of structure). Some combinations of amino acids will tend to curl up
in a coil called an
α-helix or into a sheet called a β-sheet; some α-helixes can be seen
in the hemoglobin schematic above. Tertiary structure is the entire three-dimensional
shape of the protein. This shape is determined by the sequence of amino acids. In
fact, a single change can change the entire structure. The alpha chain of hemoglobin
contains 146 amino acid residues; substitution of the glutamate residue at position 6
with a valine residue changes the behavior of hemoglobin so much that it results in
sickle-cell disease. Finally, quaternary structure is concerned with the structure of a
protein with multiple peptide subunits, like hemoglobin with its four subunits. Not all
proteins have more than one subunit.
Examples of protein structures from the Protein Data Bank
Members of a protein family, as represented by the structures of the isomerase
Ingested proteins are usually broken up into single amino acids or dipeptides in
the small intestine, and then absorbed. They can then be joined to make new proteins.
Intermediate products of glycolysis, the citric acid cycle, and the pentose phosphate
pathway can be used to make all twenty amino acids, and most bacteria and plants
possess all the necessary enzymes to synthesize them. Humans and other mammals,
however, can synthesize only half of them. They cannot synthesize isoleucine,
leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These
are the essential amino acids, since it is essential to ingest them. Mammals do possess
the enzymes to synthesize alanine, asparagine, aspartate, cysteine, glutamate,
glutamine, glycine, proline, serine, andtyrosine, the nonessential amino acids. While
they can synthesize arginine and histidine, they cannot produce it in sufficient
amounts for young, growing animals, and so these are often considered essential
If the amino group is removed from an amino acid, it leaves behind a carbon
skeleton called an
α-keto acid. Enzymes called transaminases can easily transfer the
amino group from one amino acid (making it an
α-keto acid) to another α-keto acid
(making it an amino acid). This is important in the biosynthesis of amino acids, as for
many of the pathways, intermediates from other biochemical pathways are converted
α-keto acid skeleton, and then an amino group is added, often via
transamination. The amino acids may then be linked together to make a protein.
A similar process is used to break down proteins. It is first hydrolyzed into its
component amino acids. Free ammonia(NH
), existing as the ammonium ion (NH
Different tactics have evolved in different animals, depending on the animals' needs.
Unicellularorganisms, of course, simply release the ammonia into the environment.
Likewise, bony fish can release the ammonia into the water where it is quickly
diluted. In general, mammals convert the ammonia into urea, via the urea cycle.
In order to determine whether two proteins are related, or in other words to
decide whether they are homologous or not, scientists use sequence-comparison
methods. Methods like sequence alignments and structural alignments are powerful
tools that help scientists identify homologies between related molecules.
relevance of finding homologies among proteins goes beyond forming an
evolutionary pattern of protein families. By finding how similar two protein
sequences are, we acquire knowledge about their structure and therefore their
Main articles: Nucleic acid, DNA, RNA, and Nucleotides
The structure of deoxyribonucleic acid (DNA), the picture shows the
Nucleic acids, so called because of its prevalence in cellular nuclei, is the
generic name of the family of biopolymers. They are complex, high-molecular-
weight biochemical macromolecules that can convey genetic information in all living
cells and viruses.
components: a nitrogenous heterocyclic base (either a purine or a pyrimidine), a
pentose sugar, and a phosphate group.
Structural elements of common nucleic acid constituents. Because they contain
The most common nucleic acids are deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA).
The phosphate group and the sugar of each nucleotide
nitrogenous bases stores the information. The most common nitrogenous bases are
adenine, cytosine,guanine, thymine, and uracil. The nitrogenous bases of each strand
of a nucleic acid will form hydrogen bonds with certain other nitrogenous bases in a
complementary strand of nucleic acid (similar to a zipper). Adenine binds with
thymine and uracil; Thymine binds only with adenine; and cytosine and guanine can
bind only with one another.
Aside from the genetic material of the cell, nucleic acids often play a role as
second messengers, as well as forming the base molecule for adenosine triphosphate
(ATP), the primary energy-carrier molecule found in all living organisms.
cytosine, and guanine occur in both RNA and DNA, while thymine occurs only in
DNA and uracil occurs in RNA.
Main article: Carbohydrate metabolism
Glucose is the major energy source in most life forms. For instance,
polysaccharides are broken down into their monomers (glycogen phosphorylase
removes glucose residues from glycogen). Disaccharides like lactose or sucrose are
cleaved into their two component monosaccharides.
The metabolic pathway of glycolysis converts glucose to pyruvate by via a
series of intermediate metabolites. Each chemical modification (red box) is
performed by a different enzyme. Steps 1 and 3 consume ATP (blue) and steps 7 and
10 produce ATP (yellow). Since steps 6-10 occur twice per glucose molecule, this
leads to a net production of ATP.
Glucose is mainly metabolized by a very important ten-step pathway
calledglycolysis, the net result of which is to break down one molecule of glucose
into two molecules of pyruvate. This also produces a net two molecules ofATP, the
energy currency of cells, along with two reducing equivalents of converting NAD
(nicotinamide adenine dinucleotide:oxidised form) to NADH (nicotinamide adenine
dinucleotide:reduced form). This does not require oxygen; if no oxygen is available
(or the cell cannot use oxygen), the NAD is restored by converting the pyruvate to
lactate (lactic acid) (e.g., in humans) or to ethanol plus carbon dioxide (e.g., in yeast).
Other monosaccharides like galactose and fructose can be converted into
intermediates of the glycolytic pathway.
further metabolized. It is irreversibly converted to acetyl-CoA, giving off one carbon
atom as the waste product carbon dioxide, generating another reducing equivalent as
NADH. The two molecules acetyl-CoA (from one molecule of glucose) then enter the
citric acid cycle, producing two more molecules of ATP, six more NADH molecules
and two reduced (ubi)quinones (via FADH
as enzyme-bound cofactor), and
quinol molecules then feed into the enzyme complexes of the respiratory chain, an
electron transport system transferring the electrons ultimately to oxygen and
conserving the released energy in the form of a proton gradient over a membrane
(inner mitochondrial membrane in eukaryotes). Thus, oxygen is reduced to water and
the original electron acceptors NAD
and quinone are regenerated. This is why
transferring the electrons from high-energy states in NADH and quinol is conserved
first as proton gradient and converted to ATP via ATP synthase. This generates an
additional 28 molecules of ATP (24 from the 8 NADH + 4 from the 2 quinols),
totaling to 32 molecules of ATP conserved per degraded glucose (two from
glycolysis + two from the citrate cycle).
It is clear that using oxygen to completely
independent metabolic feature, and this is thought to be the reason why complex life
appeared only after Earth's atmosphere accumulated large amounts of oxygen.
Main article: Gluconeogenesis
In vertebrates, vigorously contracting skeletal muscles (during weightlifting or
sprinting, for example) do not receive enough oxygen to meet the energy demand,
and so they shift to anaerobic metabolism, converting glucose to lactate. The liver
regenerates the glucose, using a process called gluconeogenesis. This process is not
quite the opposite of glycolysis, and actually requires three times the amount of
energy gained from glycolysis (six molecules of ATP are used, compared to the two
gained in glycolysis). Analogous to the above reactions, the glucose produced can
then undergo glycolysis in tissues that need energy, be stored as glycogen (or starch
in plants), or be converted to other monosaccharides or joined into di- or
oligosaccharides. The combined pathways of glycolysis during exercise, lactate's
crossing via the bloodstream to the liver, subsequent gluconeogenesis and release of
glucose into the bloodstream is called the Cori cycle.
Relationship to other "molecular-scale" biological sciences
Schematic relationship between biochemistry, genetics, and molecular biology
Researchers in biochemistry use specific techniques native to biochemistry, but
increasingly combine these with techniques and ideas developed in the fields of
genetics, molecular biology and biophysics. There has never been a hard-line among
these disciplines in terms of content and technique. Today, the terms molecular
schematic that depicts one possible view of the relationship between the fields:
- Biochemistry is the study of the chemical substances and vital processes
occurring in living organisms. Biochemists focus heavily on the role, function, and
structure of biomolecules. The study of the chemistry behind biological processes and
the synthesis of biologically active molecules are examples of biochemistry.
- Genetics is the study of the effect of genetic differences on organisms. Often
this can be inferred by the absence of a normal component (e.g., one gene). The study
of "mutants" – organisms with a changed gene that leads to the organism being
different with respect to the so-called "wild type" or normal phenotype. Genetic
interactions (epistasis) can often confound simple interpretations of such "knock-out"
or "knock-in" studies.
- Molecular biology is the study of molecular underpinnings of the process of
replication, transcription and translation of the genetic material. The central dogma of
molecular biology where genetic material is transcribed into RNA and then translated
into protein, despite being an oversimplified picture of molecular biology, still
provides a good starting point for understanding the field. This picture, however, is
undergoing revision in light of emerging novel roles for RNA.
- Chemical biology seeks to develop new tools based on small molecules that
information about their function. Further, chemical biology employs biological
systems to create non-natural hybrids between biomolecules and synthetic devices
(for example emptied viral capsidsthat can deliver gene therapy or drug molecules).
We classify the organisms to study the diversity effectively and easily hence, it
1. We see microscopic bacteria of the range of few micrometers in size. e.g.
Plasmodium, amoeba. They live for a short span of time e.g. blue green algae etc.
2. We have bigger animals like 30 meters long or more e.g. blue whale etc. live
for long life.
3. We have even more large organisms as red wood tree of California living for
thousands of years.
The Plant Kingdom can be further classified into five divisions. Their key
characteristics are given below:
1. Thallophytic:- The plant body is simple thallus type. The plant body is not
differentiated into root, stem and leaves. They are commonly known as algae.
Examples: Spirogyra, char, Volvo, ulothtrix, etc.
2. Bryophyte:- Plant body is differentiated into stem and leaf like structure.
Vascular system is absent, which means there is no specialized tissue for
transportation of water, minerals and food. Bryophytes are also known as the
amphibians of the plant kingdom, because they need water to complete a part of their
life cycle. Examples: Moss, merchant.
3. Pteridophyta:- Plant body is differentiated into root, stem and leaf. Vascular
system is present. They do not bear seeds and hence are called cryptogams. Plants of
rest of the divisions bear seeds and hence are called phanerogams. Examples:
Marisela, ferns, horse tails, etc.
4. Gymnosperms:- They bear seeds. Seeds are naked, i.e. are not covered. The
word ‘gyms’ means naked and ‘sperm’ means seed. They are perennial plants.
Examples: Pine, cycads, deodar, etc.
5. Angiosperms:- The seeds are covered. The word ‘amigos’ means covered.
There is great diversity in species of angiosperm. Angiosperms are also known as
flowering plants, because flower is a specialized organ meant for reproduction.
Angiosperms are further divided into two groups, viz. monocotyledonous and
(a) Monocotyledonous: There is single seed leaf in a seed. A seed leaf is a baby
plant. Examples: wheat, rice, maize, etc.
(b) Dicotyledonous: There are two cotyledons in a seed. Examples: Mustard,
gram, mango, etc.
Biodiversity refers to all the diverse living organisms like plants, animals and
micro-organisms present on earth.
The organisms present in this kingdom are eukaryotic, green autotrophs and
First they are differentiated on the basis of the plant body they divided on the
basis of vascular systems then again divided them on the basis of occurrence of seed
and then furthered divided on the basis of seeds are covered or not.