This presentation intends to offer the basic features of plant metabolism along with the different types of mechanisms to regulate and control the metabolic pathways.

1. REGULATION OF METABOLISM
A Presentation by Dr. N. Sannigrahi, Associate Professor,
Department of Botany,
Nistarini College, Purulia, D.B. Road, Purulia (W.B) India

2. METABOLISM-DEFINITION
 Thus the term ‘metabolism’ of a food substance is meant by a series of
specific biochemical reactions occurring within the living organism from
the time of its incorporation into the cell or tissue till its excretion, of which
some are concerned with tissue synthesis and others with tissue breakdown
what are termed as anabolism and catabolism respectively. Although both
anabolism and catabolism are reversible biochemical reactions but growth
and loss of tissue mass (breakdown of tissue) depends on predominance of
one over the other opposite reaction.
 Metabolism-Anabolism( Construction)
 Catabolism (Destruction) but at the cost of energy & Enzymes with
little bit regulation to maintain a dynamic equilibrium.

3. PLANT METABOLISM

4. ANABOLISM
 Synthesis of many specialized substances for the organization of these
substances into the types of characteristic protoplasm of different varieties
of cells and tissues forming up the organism, resulting development growth
and maintenance of a living organism. Those reactions which are included
in the process of synthesis of larger protoplasmic molecules from lower
ones for building up tissues are collectively known as synthesis or
anabolism. Thus, anabolism is the process by which the body utilizes the
energy released by catabolism to synthesize complex molecules. These
complex molecules are then utilized to form cellular structures that are
formed from small and simple precursors that act as building blocks.
 Example: Photosynthesis, DNA Synthesis, Protein synthesis

5. CATABOLISM
 Production of energy required for the protoplasmic synthesis and other
process of the body, viz., maintenance of temperature, movement, and
generation of electrical potentials, the secretion and excretion of fluid and
transport of substances against concentration gradient. Those reactions
which are included in the process of breakdown of large protoplasmic
molecules to smaller ones for the supply of energy are collectively called
analysis or catabolism. Thus, catabolism is the branch of the metabolic
process that breaks down complex, big molecules into smaller ones,
yielding energy. It is the destructive branch of the metabolism that results
in the release of energy. Each living cell depends on energy for its
existence. Metabolism is the sum total of the essential activities that occur
in a living being for their sustenance. Catabolism and Anabolism together
form metabolism.
 Example: Respiration

6. PHOTOSYNTHESIS

7. RESPIRATION VS PHOTOSYNTHESIS

8. RESPIRATION

9. METABOLIC CONTROL VS METABOLIC REGULATION
 Very often, metabolic control and metabolic regulation are interchangeable by
the biochemists but there is a little bit difference in between the two terms as
follow:
 Metabolic control- It refers the adjustment between the output of metabolic
pathway is response to the external signal imposed upon it.
 Metabolic regulation- It occurs when an organism ,maintain some variable
relatively constant overtime despite the fluctuations in external conditions.
 Homeostasis , therefore , a consequence of metabolic regulation, which itself
may be a result of metabolic control.
 So, regulation and control of metabolic pathways are highly elaborate metabolic
systems in case of all the organisms irrespective of their individual hierarchy.

10. REGULATION OF METABOLIC PATHWAYS
 Metabolic reactions are ongoing pathways and a number of reactions take place
simultaneously during primary and secondary metabolisms. There is a urge of
the regulations and this regulation broadly takes place by the following:
 1. Product Inhibition
 2. Mass Action Ratio
 3. Allosteric Regulation
 4. Regulatory Proteins
 5. Covalent Modification
 6. Gene expression/ Transcriptional control.
 Thus, the total metabolic reactions are controlled either single or cumulative
effect of the aforesaid constituents.

11. PRODUCT INHIBITION

12. MASS ACTION ACTION
 What is the Law of Mass Action?
 The law of mass action states that the rate of a reaction is proportional to
the product of the concentrations of each reactant.
 This law can be used to explain the behavior exhibited by solutions
in dynamic equilibrium. The law of mass action also suggests that the
ratio of the reactant concentration and the product concentration is
constant at a state of chemical equilibrium.
 The Equilibrium Constant (Kc)
 The concentration of reactants and products, at equilibrium, are constant
at a given temperature. Consider the following simple reversible
reaction where A & B are the reactants whereas C & D are the products.
 A + B ⇌ C + D
 A mixture of products and reactants in a state of chemical equilibrium is
known as an equilibrium mixture. There exists a relation between the
concentration of products and the concentration of reactants for an
equilibrium mixture. This relation can be equated as follows.

13. MASS ACTION
 Kc=[c][D]/[A][B]
 Here, Kc is called the equilibrium constant. In this equation, the concentration of
A at equilibrium is represented as [A] (similarly for B, C, and D), and the
stoichiometric coefficients of the reactants and products are 1. It has been
experimentally observed that the equilibrium constant is also dependent on the
stoichiometric coefficients of the reactants and products.
 Therefore, the law of mass action dictates that the equilibrium constant, at a
given constant temperature, is equal to the product of the concentration of
products raised to the respective stoichiometric coefficients divided by the
product of the reactant concentrations, each raised to the corresponding
stoichiometric coefficient.
 This is also known as the equilibrium law or the law of chemical equilibrium.

14. ALLOSTERIC ENZYMES
 Allosteric enzymes are enzymes that have an additional binding site for effector
molecules other than the active site. The binding brings about conformational
changes, thereby changing its catalytic properties. The effector molecule can be
an inhibitor or activator.
 All the biological systems are well regulated. There are various regulatory
measures in our body, that control all the processes and respond to the various
inside and outside environmental changes. Whether it is gene expression, cell
division, hormone secretion, metabolism or enzyme activity, everything is
regulated to ensure proper development and survival.
 Allosteric is the process of enzyme regulation, where binding at one site
influences the binding at subsequent sites.

15. ALLOSTERIC ENZYME

16. PROPERITIES OF ALLOSTERIC ENZYMES
 Enzymes are the biological catalyst, which increases the rate of the reaction
.Allosteric enzymes have an additional site, other than the active site or
substrate binding site. The substrate-binding site is known as C-subunit and
effector binding site is known as R-subunit or regulatory subunit
 There can be more than one allosteric sites present in an enzyme molecule.
They have an ability to respond to multiple conditions, that influence the
biological reactions
 The binding molecule is called an effector, it can be inhibitor as well as
activator. The binding of the effector molecule changes the conformation of the
enzyme
 Activator increases the activity of an enzyme, whereas inhibitor decreases the
activity after binding. The velocity vs substrate concentration graph of allosteric
enzymes is S-curve as compared to the usual hyperbolic curve

17. REGULATION MECHANISMS
 Allosteric Regulation Mechanism
 There are two types of allosteric regulation on the basis of substrate and
effector molecules:
 Homotropic Regulation: Here, the substrate molecule acts as an effector also.
It is mostly enzyme activation and also called cooperatively, e.g. binding of
oxygen to hemoglobin.
 Heterotropic Regulation: When the substrate and effector are different. The
effector may activate or inhibit the enzyme, e.g. binding of CO2 to
hemoglobin.
 On the basis of action performed by the regulator, allosteric regulation is of
two types, inhibition and activation.
 Allosteric Inhibition: When an inhibitor binds to the enzyme, all the active
sites of the protein complex of the enzyme undergo conformational changes so
that the activity of the enzyme decreases.
 Allosteric Activation: When an activator binds, it increases the function of
active sites and results in increased binding of substrate molecules.

18. EXAMPLES OF ALLOSTERIC ENZYMES
 Aspartate Transcarbamoylase (ATCase) ATCase catalyses the biosynthesis
of pyrimidine
 Cytidine triphosphate (CTP) is the end product and also inhibits the reaction. It
is known as feedback regulation
 ATP (adenosine triphosphate), a purine nucleotide activates the process, high
concentration of ATP can overcome inhibition by CTP. This ensures the
synthesis of pyrimidine nucleotide when a high concentration of purine
nucleotide is present Acetyl-CoA carboxylase regulates the process of
lipogenesis.
 This enzyme is activated by citrate and inhibited by a long chain acyl-CoA
molecule such as palmitoyl-CoA, which is an example of negative feedback
inhibition by product
 Acetyl-CoA carboxylase is also regulated by phosphorylation/
dephosphorylation controlled by hormones such as glucagon and epinephrine
 Acetyl-CoA Carboxylase

19. MODEL OF REGULATION
 Concerted or Symmetry Model- According to this model, there is a
simultaneous change in all the subunits of an enzyme. All the subunits are either
present in R form (active form) or T form (inactive form), having less affinity to
a substrate. An inhibitor shifts the equilibrium of T ⇄ R, towards T, and
activator shifts the equilibrium towards R form and favors the binding. It
explains the cooperative regulation of activators as well as inhibitors.

20. ALLOSTERIC ENZYMES

21. ISOENZYMES
Isozymes (also known as isoenzymes or more generally as
multiple forms of enzymes) are enzymes that differ in amino acid
sequence but catalyze the same chemical reaction. Isozyme
usually have different kinetic parameters (e.g. different KM
values), or are regulated differently. They permit the fine-tuning of
metabolism to meet the particular needs of a given tissue or
developmental stage.
 In many cases, isozyme are encoded by homologous genes that
have diverged over time. Strictly speaking, enzymes with different
amino acid sequences that catalyse the same reaction are isozymes
if encoded by different genes, or allozymes if encoded by different
alleles of the same gene the two terms are often used
interchangeably.

22. ISOENZYMES

23. ISOENZYMES-FUNCTIONS
 The existence of isozymes permits the fine-tuning of metabolism to meet the
particular needs of a given tissue or developmental stage. Consider the example
of lactate dehydrogenase (LDH), an enzyme that functions in anaerobic glucose
metabolism and glucose synthesis.
 In plants, aspartate kinase which is involved in the biosynthesis of amino acids
such as lysine and alanine from aspartate is known to exist in two isozyme
forms. Ting et al, 1975 in their experiments showed the separation of three
isozyme forms of the enzyme malate dehydrogenase by starch-gel
electrophoresis from spinach leaf cells. Two of these isozymes corresponded
one each to isozymes extracted from isolated peroxisomes and mitochondria
while the third existed in cytosol.

24. COVALENT MODIFICATION
 Covalently modulated enzymes. Here, the active and inactive form of the
enzymes are altered due to covalent modification of their structures which is
catalyzed by other enzymes. This type of regulation consists of the addition or
elimination of some molecules which can be attached to the enzyme protein.
 The covalent attachment of another molecule can modify the activity of
enzymes and many other proteins. In these instances, a donor molecule provides
a functional moiety that modifies the properties of the enzyme. Most
modifications are reversible. Phosphorylation and dephosphorylation are the
most common but not the only means of covalent modification. Histones—
proteins that assist in the packaging of DNA into chromosomes as well as in
gene regulation—are rapidly acetylated and deacetylated in vivo . More heavily
acetylated histones are associated with genes that are being actively transcribed.
The acetyltransferase and deacetylase enzymes are themselves regulated by
phosphorylation, showing that the covalent modification of histones may be
controlled by the covalent modification of the modifying enzymes.

25. COVALENT MODIFICATION

26. GENE EXPRESSION & TRANSCRIPTIONAL CONTROL
 The process of reading a ‘gene’ and the production of specific protein through
transcription and translation is called gene expression.
 Thus, there are two steps involved-
 TRANSCRIPTION- The reading of the specific ‘gene’,
 TRANSLATION- The building of the protein with reference to the specific
transcripted information from there after.
 Every living organisms contain instructions embedded in the recipe of life
called DNA and DNA it is the ‘cookbook’ of the entire body of the living
organism and the number of ‘servings’ of each protein is determined by the
amount of mRNA made in each cell. Thus, the DNA is the code of life and it
performs as the template for the synthesis of diverse types of proteins which are
to be synthesized as far as the signal faced by the corresponding counterpart.
Therefore, it is very often said, life is a three letters word and four letters
alphabet.

27. REGULATION OF GENE EXPRESSION

28. REGULATION OF GENE EXPRESSION
 Plant secondary metabolites play critical roles in plant-environment
interactions. They are synthesized in different organs or tissues at particular
developmental stages, and in response to various environmental stimuli, both
biotic and abiotic.
 Accordingly, corresponding genes are regulated at the transcriptional level by
multiple transcription factors. Several families of transcription factors have been
identified to participate in controlling the biosynthesis and accumulation of
secondary metabolites.
 These regulators integrate internal (often developmental) and external signals,
bind to corresponding cis-elements — which are often in the promoter regions
— to activate or repress the expression of enzyme-coding genes, and some of
them interact with other transcription factors to form a complex

29. TRANSCRIPTION & TRANSLATION

30. REGULATION OF GENE EXPRESSION
 The spatial, temporal, and inducible formation of secondary metabolites and the
transcripts of corresponding biosynthetic genes are under tight regulation at
different levels, in which transcriptional regulation via transcription factors has
been investigated intensively. Transcription factors are sequence-specific DNA-
binding proteins that interact with the regulatory (often promoter) regions of the
target genes, and modulate the rate of transcriptional initiation by RNA
polymerase (Vom Endt et al. 2002).
 They can integrate internal (often developmental) and external (environmental)
signals to regulate enzyme gene expression, thus controlling the specific
accumulation of secondary metabolites.
 Some transcription factors of different types form complexes to activate or
suppress downstream gene expression. Several families of transcription factors
act as regulators of plant secondary metabolism.

31. THANKS A LOT TO VISIT THE PAGE
 References:
I. Google for images,
II. Different WebPages to enrich the domain,
III. Plant Physiology- Taiz & Zeiger
IV. Fundamentals of Biochemistry- Jain, Jain & Jain
V. Biochemistry & Molecular Biology- Wilson & Walker.
Disclaimer: This presentation has been developed to enrich online domain for
free accession without any kind of financial interest.

32. AWESOME MARVEL OF METABOLIC REGULATION