Transcript Biosynthesis of Plant Primary metabolitesx

Plant Metabolism,
their Biochemical Pathways
&
Production of 10 Metabolites
By
Dr. M. RAMAIAH,
M. Pharm., Ph.D., IPDRA, DICT(USA)
Associate Professor & HOD
Department of Pharmacognosy&Phytochemistry
Hindu College of Pharmacy,
Guntur, A.P. India
Living plants are solar-powered biochemical and
biosynthetic laboratory which manufactures both primary
and secondary metabolites from air, water, minerals and
sunlight.
The group of pathways synthesizing simpler but essential
molecules for normal physiological growth and energy
requirements of plants is called primary metabolism and the
products are called primary metabolites. They are widely
distributed in nature and are also utilized as food by man.
Eg: Sugars, amino acids, coA, mevalonic acid, nucleic acid
etc
Secondary metabolites are useless for plants and stored in
various parts of plants restricted in their distribution are
derived biosynthetically from primary metabolites. These
are organic compounds that are not directly involved in the
normal growth, development, or not necessary for the plant
cells themselves but may be useful for the plant as a whole.
Since these don’t have primary function so they are called
secondary metabolites. They have Pharmaceutical
importance.
Eg: Alkaloids, glycosides, tannins, flavanoides, terpenoides,
and eseential oils
Relationship between primary and secondary metabolism:
• The processes and products of primary metabolism are
similar in most organisms, while those of secondary
metabolism are more specific.
• In plants, primary metabolism is made up of photosynthesis,
respiration, etc., using CO2, H2O, and NH3 as starting
materials, and forming products such as glucose, amino acids,
nucleic acids. These are similar among different species.
• In secondary metabolism, the biosynthetic steps, substrates
and products are characteristic of families and species.
Species which are taxonomically close display greater
similarities (and metabolites); those which are distant have
greater differences.
3. Secondary metabolites and
Biosynthesis (Dayrit)
4
Biogenesis: overview of the origin of compounds starting from
the set of intermediate building blocks: acetyl-CoA, MVA and
MEP, shikimic acid, and the amino acids phenylalanine and
tyrosine, tryptophan, ornithine and lysine.
HO
CH3
NH2
CO2H
CO2H
O
CO2H
SCoA
R
CO2H
OH
HO
HO CH3
OH
HO
H2N
NH2
CO2H
OH
OH
N
H
NH2
NH2
H2N
CO2H
OP
Biosynthesis: detailed study of the step-wise formation of
secondary metabolites. At more detailed levels, the specific
enzymes, genes and signals are also identified.
3. Secondary metabolites and
Biosynthesis (Dayrit)
5
Biosynthetic reactions are replica of common organic
reactions like catalytic reactions, phosphorylation, hydride
transfer, oxidation, elimination, acylation, alkylation,
reduction, condensation, rearrangement etc. These are
dependent on different conditions such as catalysts, type of
energy and nature of medium during the course of reaction.
The elucidation of biosynthetic pathway in plants for
production of various metabolites has been extensively
examined by means of isotopically labeled precursors.
Cell Metabolism
Cell metabolism is the process by which living cells
process nutrient molecules and maintain a living state.
Metabolism has two distinct divisions:
Anabolism, in which a cell uses energy and reducing power to
construct complex molecules and perform other life functions
such as creating cellular structure; and
Catabolism, in which a cell breaks down complex molecules
to yield energy and reducing power. Cell metabolism involves
extremely complex sequences of controlled chemical reactions
called metabolic pathways
Metabolic Pathway
In biochemistry, a metabolic pathway is a series of
chemical reactions occurring within a cell , catalyzed by
enzymes, resulting in either the formation of a metabolic
product to be used or stored by the cell, or the initiation of
another metabolic pathway (then called a flux generating
step). Many pathways are elaborate, and involve a step by
step modification of the initial substance to shape it into the
product with the exact chemical structure desired.
Major Metabolic Pathways
Cellular respiration:
Glycolysis
Anaerobic respiration
Kreb’s cycle / Citric acid cycle
Oxidative phosphorylation
Creation of energetic compounds from non-living matter:
Photosynthesis (plants, algae, cyanobacteria )
Chemosynthesis (some bacteria)
Other pathways occurring in (most or) all living organisms
include:
Fatty acid oxidation (β-oxidation)
Gluconeogenesis
HMG-CoA reductase pathway (isoprene prenylation)
Pentose phosphate pathway (hexose monophosphate)
Porphyrin synthesis (or heme synthesis) pathway
Urea cycle
Metabolites
Metabolites are the intermediates and products of
metabolism . The term metabolite is usually restricted to
small molecules . A primary metabolite is directly involved
in the normal growth, development, and reproduction. A
secondary metabolite is not directly involved in those
processes, but usually has important ecological function.
Induction of secondary metabolism: The induction of
secondary metabolism is linked to particular environmental
conditions or developmental stages. For example, when
grown in a nutrient-rich medium, most bacteria employ
almost solely basic metabolism in order to grow and
reproduce. However, when nutrients are depleted, they start
producing an array of secondary metabolites in order to
promote survival.
Plants produce secondary metabolites as a response to
adverse environmental conditions or in particular
developmental stages.
Eg: Exposure to UV radiation induces the biosynthesis of
UV-absorbing compounds
Secondary metabolites are those chemical compounds
function or importance of these compounds to the organism
is usually of an ecological nature as they are used as
defenses against predators, parasites and diseases, for
interspecies competition, and to facilitate the reproductive
processes (coloring agents, attractive smells, etc). Since
these compounds are usually restricted to a much more
limited group of organisms, they have long been of prime
importance in taxonomic research.
Formation of primary metabolites
Biogenesis in-vivo synthesis of both primary and secondary
metabolites is started with the photosynthesis to produce sugar
molecules which are metabolized to glycerates, pyruvates and
finally acetyl CoA.
This acetyl CoA is used in TCA cycle to generate number
of amino acids and excess is to synthesize fatty acids.
Few of the acetyl CoA molecules are condensed to form
mevalonic acid, precursor of synthesis of steroids and terpenoides.
Amino acids give rise to alkaloids.
The intermediates of glycolysis i.e., glyceraldehyde-3phosphate and erythrose-4-phosphate from pentose phosphate
pathway yields shikimic acid which is main precursor for
biosynthesis of important aromatic compounds like
phenylpropanoides, lignin, lignans, flavanoides and terpenoid
quinones.
Photosynthesis
Photosynthesis is the process where plants convert sunlight
into energy, then store it as carbohydrates, sugars, such as
glucose. Photosynthesis may be the most important process in
ecosystems, both brings in energy needed within the
ecosystem, and produce oxygen (O2) needed for cellular
respiration , and the production of more ATP.
Photosynthesis has three basic steps:
1. Energy is captured from the sunlight.
2. Light energy is converted into chemical energy in the form
of ATP and NADPH.
3. Chemical energy is used to power the synthesis of organic
molecules (e.g. carbohydrates) from carbon dioxide (CO2).
Plant Metabolism
The products of photosynthesis provide not only the substrate material
but also chemical energy for all subsequent biosynthesis.
The simplest equation for the photosynthesis:
In the first stage, light-dependent reactions capture the energy of light
and use it to make the energy-storage molecules ATP and NADPH via
ATP synthase.
In the second stage, the light-independent reactions also
known as Calvin cycle reduces carbon dioxide via enzyme ribulose-1, 5diphosphate carboxylase oxygenase (RuBisCO). The product of Calvin
cycle is 3-carbon compound, glyceraldehyde-3-phosphate and water. 2
molecules of glyceraldehyde-3-phosphate combine to form 1 molecule
of glucose and latter different larger carbohydrates.
Ribulose-1, 5-diphosphate carboxylase
oxygenase
Glycolysis (Embden-meyerhoff pathway)
Glycolysis is the process of enzymatic reactions that converts glucose
into 3-carbon compounds (pyruvate and glycerates), small amounts of
ATP and NADH (reducing power).
Glycolysis represents an anabolic pathway common in both
aerobic and anaerobic organisms.
Sugars and polysaccharides are transformed into glucose or one of
its phosphorylated derivatives before being processed any further. In the
course of degradation, ATP is produced. Pyruvate may be regarded as the
preliminary final product of the degradation. Pyruvate is fed into the citric
acid cycle via an intermediate product. This pathway produces energy in the
form of ATP. The starting product glucose is completely oxydized to water
and carbon dioxide.
Main Functions of Glycolysis
 Provide ATP energy
 Generate intermediates for other pathways
(the most important is pyruvate).
Citric Acid Cycle (Kreb’s cycle)
The citric acid cycle, also known as the
tricarboxylic acid (TCA) cycle or the Kreb’s cycle is
the common mode of oxidative degradation of
carbohydrate, fatty acid, and amino acid in
eukaryotes and prokaryotes.
It accounts for the major portion of
carbohydrate, fatty acid and amino acid oxidation
and produces at the same time a number of
biosynthetic precursors.
Each mole of pyruvate which enters the TCA
cycle, 12 moles of ATP can be generated
Pentose Phosphate pathway
The pentose phosphate pathway also called the phosphogluconate
pathway or hexose monophosphate (HMP) shunt, is a process that
generates NADPH and 5-carbon sugars, pentoses.
This pathway is an alternative to glycolysis. There are
two distinct phases in the pathway. The first is the oxidative phase,
in which NADPH is generated, and the second is the non-oxidative
synthesis of pentoses.
The role of this pathway is:
 Production of NADPH
 Production of ribose-5-phosphate used in the synthesis of
nucleotides and nucleic acids
 Production of erythrose-4-phosphate used in the shikimic acid
pathway, synthesis of aromatic amino acids.
Biogenetic classification of natural products
Biogenesis
Intermediate
Structural Types
Acetogenins
acetyl CoA
fats and lipids,
macrolides, phenols
Terpenoids
mevalonic acid,
methyl erythritol phosphate
monoterpenes, sesquiterpenes,
diterpenes, triterpenes, steroids
carotenoids
Shikimates
shikimic acid, prephenic acid
phenylpropanoids, phenols
flavonoids
Aliphatic alkaloids
lysine, ornithine
aliphatic alkaloids
Aromatic alkaloids
phenylalanine, tyrosine,
tryptophan
aromatic alkaloids
3. Secondary metabolites and
Biosynthesis (Dayrit)
30
PRIMARY METABOLITES
INTERMEDIATE METABOLITES
SECONDARY METABOLITES
CO2H
CO 2
+
H2O
Pentose phosphate
Erythrose-4-phosphate
Glucose
HO
OH
OH
Shikimate
Phosphoenol pyruvate
+
Polysaccharides
NH 3
CO2H
NH2
R
CO2H
Citric acid
cycle
Pyruvate
N
H
Aromatic compounds
(C 6-C1; C6-C2)
Phenylpropanoids (C
Lignans
6
C3)
*
Aromatic alkaloids
Aromatic
amino acids
Mixed alkaloids
NH2
Aliphatic
amino acids
Aliphatic alkaloids
H2N
CO2H
NH2
NH2
H2N
CO2H
O
SCoA
Acetyl-CoA
Polyketides
Polyphenols
Flavonoids
Phenylpropanoids
Fatty acids
HO
Overview of
Secondary
Metabolism
* Metabolites found in
higher organisms only
Polyacetylenes
Prostaglandins
CH3
Mevalonic acid
CO2H
*
OH
Terpenes
Steroids
Carotenoids
Iridoids
3. Secondary metabolites and
Aliphatic
amino acids
Biosynthesis (Dayrit)
Alkaloids
32
*