Pharmacognosy and Phytochemistry-II

BP504T
Module-1
Metabolic Pathways in Higher Plants
and Their Determination

Sakshi Priya
Assistant Professor
PCTE Group of Institute
 Module 01
Metabolic Pathways in Higher Plants and Their
Determination

 Brief study of basic metabolic pathways and formation of

different secondary metabolites through these pathways-
 Shikimic acid pathway
 Acetate pathways
 Amino acid pathway
 Study of utilization of radioactive isotopes in the investigation of
Biogenetic studies.
 Basic metabolic pathway
 The sum total of all the enzymatic mediated reactions occurring in the
cell is collectively called metabolism.
 The reaction sequences occurring within organisms in an orderly and
regulated way are known as metabolic pathways and the compounds
formed during metabolism are called metabolites.
 During the process of metabolism many intermediate metabolites are
formed which is used to denote the chemical pathways of metabolism.
Cellular metabolism has four functions:
1. To obtain chemical energy, i.e ATP, through the degradation of energy-
rich biomolecules.
2. To transform biomolecules into building blocks or precursors needed for
the synthesis of macromolecular cell components.
3. To assemble building blocks into proteins, nucleic acids, lipids and other
cell components.
4. To form and degrade biomolecules required in the specialized functions of
cells.
 Metabolism
Metabolism is a chemical reaction in plants and animals that
changes food into energy and helps them to grow.

Catabolism Anabolism
Catabolism is the set of Anabolism refers to the
metabolic pathways that metabolic pathways that
break down complex construct complex molecules
molecules into simpler from simpler ones, requiring
ones, releasing energy in energy.
the process.
Enzymes:
Enzymes are biological catalysts—mostly proteins—that speed up chemical
reactions in living organisms without being used up themselves.
Key Features:
•Found in all living cells (plants, animals, microorganisms).
•Highly specific to the reaction they catalyze.
•Work best under specific pH and temperature.
•Help in both metabolic and biosynthetic reactions.

Enzymes help in the biosynthesis of important plant metabolites

like alkaloids, flavonoids, terpenoids, etc.
Coenzymes:
Coenzymes are non-protein organic molecules that bind to enzymes and help
them perform their catalytic activity.
Key Features:
•Not enzymes themselves, but assist enzymes.
•Often derived from vitamins (like B-complex) i.e. NAD⁺, FAD, Coenzyme
A.
•Temporarily bind to the active site of the enzyme.
•They may transfer electrons, atoms, or functional groups.

Coenzymes are important in the biosynthetic pathways of

Metabolic Pathway:
A metabolic pathway is a series of linked chemical reactions that take
place inside a cell, where the product of one reaction becomes the starting
material for the next. These pathways help in the conversion of nutrients into
energy or useful substances.

Metabolic pathways in plants are responsible for the biosynthesis of

secondary metabolites like alkaloids, flavonoids, terpenoids, etc., which
have medicinal properties.
Metabolites:
Metabolites are the small molecules that are formed as intermediates or
end products during metabolic reactions in living organisms.
As a result of metabolic process in plants, plant synthesizes primary
plant metabolites and secondary plant metabolites.

Primary Plant
Feature Secondary Plant Metabolites
Metabolites
Basic plant constituents Compounds derived from primary
Definition essential for life metabolites with specific ecological
processes. functions.
Sugars, amino acids, Alkaloids, glycosides, tannins,
Examples lipids, Coenzyme A, flavonoids, terpenoids, volatile oils,
mevalonic acid, starch. quinine.
Feature Primary Plant Metabolites Secondary Plant Metabolites
Found in all plants and plant Found in specific plant species
Distribution
parts; widely distributed. or families; limited distribution.
Present in small or trace
Quantity Present in large quantities.
amounts.
Involvement in Directly involved in growth, Not directly involved in growth
Plant Functions development, and reproduction. or development.
Biological/ Generally, do not have Have specific biological or
Pharmacologica biological or pharmacological pharmacological effects on
l Action activity. humans, animals, or pathogens.
Help in defense, protection,
Provide energy, structural stress response, and interaction
Function in
components, and primary with environment (e.g.,
Nature
metabolic functions. deterrents to herbivores,
pathogens).
BASIC METABOLIC PATHWAY
 SHIKMIC ACID PATHWAY
 The shikimate pathway provides an alternative route to aromatic
compounds, particularly the aromatic amino acids L-phenylalanine,
L-tyrosine, and L-tryptophan.
 This pathway is employed by microorganisms and plants, but not by
animals, and accordingly the aromatic amino acids feature among
those essential amino acids for human beings, to be obtained from the
diet.
 Shikimic acid is named after the highly toxic Japanese shikimi
(Illicium anisatum) flower from which it was first isolated.
•The Shikimic acid pathway is a key intermediate from carbohydrate for the
biosynthesis of C₆-C₃ units (phenyl propane derivative).
•The Shikimic acid pathway converts simple carbohydrate precursors derived
from glycolysis and the pentose phosphate pathway to the aromatic amino
acids.
•The shikimate pathway is a 7-step metabolic route used by bacteria,
fungi, algae, parasites, and plants for the biosynthesis of aromatic amino
acids (phenylalanine, tyrosine, and tryptophan).
•This pathway is not found in animals; therefore, phenylalanine and
tryptophan represent essential amino acids that must be obtained from
the animal's diet.
• Animals can synthesize tyrosine from phenylalanine,
and therefore is not an essential amino acid except for
individuals unable to hydroxylate phenylalanine to
tyrosine
SHIKMIC ACID PATHWAY
SHIKMIC ACID PATHWAY
SHIKMIC ACID PATHWAY
Uses of the Shikimic Acid Pathway
1. Biosynthesis of Aromatic Amino Acids
The primary function of the shikimic acid pathway is to synthesize the
aromatic amino acids:
Phenylalanine
Tyrosine
Tryptophan
These amino acids are precursors for proteins and secondary metabolites.
2. Production of Secondary
Metabolites
•It provides precursors for:
These compounds are important
• Alkaloids
for:
• Flavonoids • Plant defense mechanisms
• Tannins • Antioxidant properties
• Lignin • Medicinal uses
• Coumarins
• Phenolic acid (eg., gallic acid,
ferulic acid)
 In the pharmaceutical industry, shikimic acid from the Chinese star anise
(Illicium verum) is used as a base material for the production of
oseltamivir
 Shikimate can be used to synthesize (6S)-6-Fluoroshikmic acid, an
antibiotic which inhibits aromatic biosynthetic pathway.
 Glycophosphate, the active ingredient in the herbicide Roundup,
kills plant by interfering with the shikimate pathways in plants.
 More specifically glycophosphate inhibits the enzyme 5-
enolpyurvlshikimate-3-phosphate synthase (EPSPS). “Roundup Ready”
genetically modified crops overcome that inhibition
 Acetate Pathway

The acetate pathway (also called the acetyl-CoA pathway or polyketide pathway)
is a biosynthetic route primarily responsible for the formation of fatty acids,
polyketides, and other important secondary metabolites. It is widely found in
plants, fungi, bacteria, and animals.
 Acetate Pathway

 Since a long time it was believed that acetic acid is involved in the synthesis of
cholesterol, squalene and rubber-like compounds.
 The discovery of acetyl coenzyme A further supported the role of acetic acid in
biogenetic pathways.
 Later, mevalonic acid was found to be associated with the acetate.
 The pathway begins with acetyl CoA molecule produced from pyruvic acid, which is
the end product of glycolysis.
 ACETATE PATHWAY
Glycolysis Pyruvate Acetyl Co-A TCA
End
product

Acetate mevalonate pathway Acetate melonate pathway-

Mevalonic acid Malonyl Co-A

Isoprenoids
Long chain fatty acids &
polyketides

Squalene terpenes & steroids

Lipids, fats , waxes
Steroids
 TYPES OF COMPOUNDS SYNTHESIZED FROM ACETATE
PATHWAY
Iso Pentenyl Pyrophosphate + Di Methyl Allyl Pyro Phosphate (active isoprene units)
CONDENSES
Monoterpenes-Menthol, limonene, geraniol,
Geranyl pyro PO4 (C10)
linalool, citral
IPP
Farnesyl PP sesquiterpenes- termerone, zingiberene, abscisic acid,
C15 santalone
IPP
Di Taxol
C-30 terpenes
2 Geranyl IPP +
GPP C-20 Poly terpenes Rubber
Squalene 2GGPP
Tetraterpenes
Gibberellins C-40 Carotenoids, lycopene,
Steroids Terpenoids
Phytol β carotene
Solanine, 29
diosgenin
Acetate-Mevalonate Pathway
 Acetate-Mevalonate Pathway
🔬 Biological Significance:
1. Fatty Acid Biosynthesis:
•Acetate units join to form long-chain fatty acids via fatty acid synthase.
•Example: Palmitic acid (C16) from 1 acetyl-CoA + 7 malonyl-CoA.
2. Polyketide Biosynthesis:
•In microorganisms and plants, the acetate pathway is modified to form polyketides (a class of
antibiotics and anticancer agents).
•Example: Erythromycin is a polyketide antibiotic made via this pathway.
3. Secondary Metabolites in Plants:
•Used in the biosynthesis of flavonoids, anthraquinones, stilbenes, and tannins.
•These are phenolic compounds that play a role in defense, pigmentation, and UV protection.
 REFERENCES
 Medicinal Natural Products: A Biosynthetic Approach, Paul M. Dewick, 3rd
Ed. 2009, John Wiley & Sons, Ltd. England .
 The Biosynthesis
of secondary metabolites, R.B. Herbert, 1st Ed. 1981,
Chapman & hall, London.
 Pharmacognosy, C.K. Kokate, A.P. Purohit, S.B. Gokhale, 54th Ed.
2017, Nirali Publication, New Delhi
 Trease and Evans Pharmacognosy, W.C. Evans, 15th Ed. Elsevier,
2002.
 https://www.slideshare.net