The above documents describes the various ways of production of primary and secondary metabolites by plants.

1. Biosynthetic pathways for
natural products
Dr. Mbinji Omale

2. Biosynthesis of primary metabolites
• Living plants are solar-powered biochemical and biosynthetic laboratory which
manufactures both primary and secondary metabolites from air, water, minerals
and sunlight.
• The primary metabolites like sugars, amino acids and fatty acids that needed for
general growth and physiological development of plant which distributed in nature
and also utilized as food by man.
• The secondary metabolites such as alkaloids. Glycosides. Flavonoids, volatile oils
etc. are biosynthetic derived from primary metabolites.

3. • Cell metabolism: Process by which living cell process nutrients molecule and living state.
• Metabolic pathway: A complete set of chemical reaction that occur in living cells, allowing cells to
grow and reproduce, maintain their structure and respond to their environments.
• Living cell require energy for biosynthesis, transport of nutrient, motility and maintenance.
• Energy is obtained from the catabolism of carbon compounds (carbohydrate).
• Carbohydrates are synthesized from CO2 and H2O in the presence of light by photosynthesis.

5. • Metabolites Intermediates and products of metabolism
• A primary metabolite is directly involved in the normal growth,
development and reproduction.
• Secondary metabolite is not directly involved in those process, but
usually has important ecological function.

6. Basic biosynthetic pathways
1. Calvin cycle
precursor for carbohydrates
2. Acetate mevalonate pathway
precursor for steroids, terpenoids
3. Acatate malonate pathway
precursor for fatty acids
5. Shikimic acid pathway
precursor for aromatic amino acids
6. Amino acid pathway
precursor for aliphatic amino acids
7. 1-deoxy-D-xylulose (triose/pyruvate) pathway
precursor for hopane type triterpenoids

8. Biosynthesis of carbohydrates
• Carbohydrates are the products of photosynthesis, a biological process that converts light
energy into chemical energy
• All green plants and certain algae and bacteria have the capacity to synthesize adenosine
triphosphate (ATP) and nicotine adenine dinucleotide phosphate (NADPH).
• These compounds mediate most of the biosynthetic reactions in plants. There are basically
two primary lights:
1. Absorption of light by chlorophyll or energy transfer to chlorophyll by other light absorbing
pigments leading to production of ATP and NADPH.
2. Photolysis of water to produce oxygen and electrons which are transferred via carrier species
and produces ATP and NADPH, two reactive molecules which work as activating and reducing
agents
Hill reaction; named after the English
biochemist Robert Hill, 1899–1991

9. • ATP is a coenzyme and the high energy of the terminal phosphate bond is available to the organism for the supply
of the energy necessary for endergonic reactions. The Hill reaction produces free oxygen hydrogen ions which
bring about the conversion of the electron carrier, NADP, to its reduced form NADPH.
• In this complicated process, two systems,
Photosystem I and Photosystem II (also known as pigment systems I and II)
Photosystem II produces ATP and Photosystem I supplies all the reduced NADP and some ATP.
In these light reactions the chlorophyll molecule captures solar energy and electrons become excited and move to
higher energy levels; on returning to the normal low-energy state, the electrons give up their excess energy, which is
passed through a series of carriers (including in the case of Photosystem II plastoquinone and several cytochromes) to
generate ATP.
Photosystem I involves an electron acceptor and the subsequent reduction of ferredoxin in the production of NADPH

10. PHOTOSYNTHESIS
• H2O + Light +ADP + P O2 + ATP + e-
• After the above steps occur in photosystem II, the electron is finally sent to
photosystem I, where the following happens
• E- + NADP + H NADPH
• Now there are two high energy molecules. Fully charged and ready to be used.
Plants make more energy that it needs immediately, so the NADPH and ATP are
used to make different sugars in Blackmann reaction.
• In the subsequent ‘dark reaction’, carbon dioxide is reduced to produce four, five,
six, and seven carbon sugars. The path of carbon in photosynthesis was first given
by Calvin is termed as Calvin cycle.

14. Glycolysis
• Glycolysis represents an anabolic pathway in plants
• Sugars and polysaccharides are transformed into glucose or one of its
phosphorylated derivatives before being processed any further. In course of
degradation, ATP is produced.
• Pyruvate may be regarded as the final product of the degradation. Pyruvate is fed
into citric acid cycle via an intermediates products.
• This pathway produces energy in the forms of ATP, the starting products glucose is
completely oxidized to water and carbon dioxide

16. • Thus degradation of carbohydrates and sugars generally proceeds via the well-
characterized pathways known as glycolysis and the Krebs/citric acid/tricarboxylic acid
cycle, which release energy from the organic compounds by oxidative reactions.
• In contrast to these primary metabolic pathways, which synthesize, degrade, and generally
interconvert compounds commonly encountered in all organisms, there also exists an area
of metabolism concerned with compounds which have a much more limited distribution in
nature.
• Such compounds, called ‘secondary metabolites’, are found in only specific organisms, or
groups of organisms, and are an expression of the individuality of species.
• Secondary metabolites are not necessarily produced under all conditions, and in the vast
majority of cases the function of these compounds and their benefit to the organism is not
yet.

17. • Some are undoubtedly produced for easily appreciated reasons, for example,
as toxic materials providing defense against predators,
as volatile attractants towards the same or other species,
as colouring agents to attract or warn other species,
But it is logical to assume that all do play some vital role for the well-being of
the plant.
It is this area of ‘secondary metabolism’ that provides most of the
pharmacologically active natural products.

18. The building blocks for secondary metabolites
• The building blocks for secondary metabolites are derived from primary
metabolism.
• The metabolites from the fundamental processes of photosynthesis, glycolysis, and
the Krebs cycle are the energy-generating processes that provide biosynthetic
intermediates.
• By far the most important building blocks employed in the biosynthesis of
secondary metabolites are derived from the intermediates
acetyl coenzyme A (acetyl-CoA),
shikimic acid,
mevalonic acid,
and 1-deoxyxylulose 5-phosphate.
These are utilized respectively in the acetate, shikimate, mevalonate, and
deoxyxylulose phosphate pathways.
Other building blocks based on amino acids are frequently employed in natural
product synthesis. Peptides, proteins, alkaloids, and many other compounds are
derived from amino acids.

20. Shikimic acid pathway
• It’s a key intermediate from carbohydrates for the biosynthesis of C6-C3 units (phenyl propane derivatives).
• The shikimic pathway converts simple carbohydrate precursor derived from glycolysis and pentose phosphate
pathway to the aromatic amino acids.
• It’s a 7 step metabolic route used by plants for the biosynthesis of aromatic amino acids (phenylalanine,
tyrosine and tryptophan).
• This pathway is not found in animals hence phenylalanine and tryptophan-essential amino acids.
• Animals can synthesize tyrosine from phenylalanine, therefore is not an essential amino acid except for
individuals unable to hydroxylate phenylalanine to tyrosine.
• The shikimic acid pathway leads to; phenols, cinnamic acids, lignans and alkaloids

23. Acetate mevalonate/ mevalonic acid/
isoprenoids / methylerythritol pathway
• The acetate is utilized in the form of Acetly CO-A, as the active form of
acetate.

24. • Mevalonate pathway plays a critical role in biosynthesis of isoprenoid
derivatives
• Acetyl CoA is the precursor of this pathway.
• Mevalonic acid is the major intermediate
• Terpenoids and steroids can be formed through this pathway

27. • Acetate mevalonate pathway is basic metabolism pathway which is useful for biosynthesis of varies secondary
metabolites like hemiterpenes, sesquiterpenes, carotenoids, squalene, steroids etc.
• The mevalonate pathway begins with acetyl-CoA and ends with production of isopentenyl pyrophosphate (IPP)
and dimethyl pyrophosphate (DMAPP) which are used to make isoprenoids, a diverse class of 30,000
biomolecules such as cholerestrol, vitamin K, and all steroid hormones.
• The terms terpenoid and isoprenoid are interchangeable, isoprenoid referring to the five-carbon isoprene unit
from which all terpenoids are theoretically derived

28. Acetate-malonate pathway
• Includes synthesis of fatty acids and aromatic compounds with the help of
secondary metabolites.
• Main precursor of acetate-malonate pathway are acetyl-CoA and malonyl-CoA.
• End product of this pathway can be saturated or unsaturated fatty acids, acetyl
easters, amides or polyketides.
• Polyketides are secondary metabolites which further synthesize aromatic
compounds by polyketide pathway.

29. acyl carrier protein (ACP)

30. 1-deoxy-D-xylulose (triose/pyruvate) pathway
• Following its discovery in 1956 mevalonic acid came to be considered the essential
precursor for all isoprenoid syntheses.
• However, in 1993 M. Rohmer et al showed that a nonmevalonate pathway existed for the
formation of hopane-type triterpenoids.
• The novel putative precursor was identified as 1-deoxy-d-xylulose-5-phosphate, formed
from glucose via condensation of pyruvate and glyceraldehyde-3-phosphate.
• Subsequent steps including a skeletal rearrangement afford isopentenyl pyrophosphate—
the same methyl-branched isoprenoid building block as formed by the MVA route.

31. Amino acid pathway
• All amino acids are derived from the intermediates in glycolysis, the citric
acid cycle, or pentose pathway.
• Nitrogen enters the pathway by way of glutamine
• Organisms vary greatly in their ability to synthesize the 20 common amino
acids
• Whereas most bacteria and plants can synthesize all 20, mammals can
synthesize about half of them.
• The remaining essential amino acids, must be obtained from food.
• Amino acids are the precursor of some secondary metabolites eg alkaloids
• Plant synthesize all 20 amino acids (aliphatic, aromatic and heterocyclic).
• Nitrogen enters metabolic reaction by reductive amination.

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