Biosynthetic Pathways of Secondary Metabolites PDF

Biosynthetic pathways of Secondary metabolites INTRODUCTION Metabolism -Metabolism constituents all the chemical transformations occurring in the cells of living organisms and these transformations are essential for life of an organism. Metabolites -End product of metabolic processes and intermedia...

Biosynthetic pathways of Secondary metabolites INTRODUCTION Metabolism -Metabolism constituents all the chemical transformations occurring in the cells of living organisms and these transformations are essential for life of an organism. Metabolites -End product of metabolic processes and intermediates formed during metabolic processes. Primary metabolites : A primary metabolite is a kind of metabolite that is directly involved in normal growth, development, and reproduction. It usually performs a physiological function in the organism (i.e. an intrinsic function). It is also referred to as a central metabolite, which has an even more restricted meaning (present in any autonomously growing cell or organism). Primary metabolites are typically formed during the growth phase as a result of energy metabolism, and are deemed essential for proper growth. Examples of primary metabolites include alcohols such as ethanol, lactic acid, and certain amino acids. Within the field of industrial microbiology, alcohol is one of the most common primary metabolites used for large-scale production. Additionally, primary metabolites such as amino acids including L-glutamate and L- lysine, which are commonly used as supplement which are isolated via the mass production of a specific bacterial species, Corynebacteria glutamicum. Another example of a primary metabolite commonly used in industrial microbiology includes citric acid. Citric acid, produced by Aspergillus niger, is one of the most widely used ingredients in food production. It is commonly used in pharmaceutical and cosmetic industries as well. Secondary metabolite Secondary metabolites are typically organic compounds produced through the modification of primary metabolite synthases. Secondary metabolites do not play a main role in growth, development, and reproduction like primary metabolites do, and are typically formed during the end or near the stationary phase of growth. Many of the identified secondary metabolites have a role in ecological function, including defense mechanism, by serving as antibiotics and by producing pigments. Examples of secondary metabolites with importance in industrial microbiology include atropine and antibiotics such as erythromycin and bacitracin. Atropine, derived from various plants, is a secondary metabolite with important use in the clinic. Atropine is a competitive antagonist for acetylcholine receptors, specifically those of the muscarinic type, which can be used in the treatment of bradycardia. Antibiotics such as erythromycin and bacitracin are also considered to be secondary metabolites. Erythromycin, derived from Saccharopolyspora erythraea, is a commonly used antibiotic with a wide antimicrobial spectrum. It is mass produced and commonly administered orally. Lastly, another example of an antibiotic which is classified as a secondary metabolite is bacitracin. Bacitracin, derived from organisms classified under Bacillus subtilis, is an antibiotic commonly used a topical drug. Photosynthesis Photosynthesis: is the process by which light energy is captured, converted and stored in a simple sugar molecule. This process occurs in chloroplasts and other parts of green organisms. It is a backbone process, in the sense that all life on earth depends on it’s functioning. The following equation sums up the process: 6CO2 (carbon dioxide) + 12 H2O (water) + light energy -> C6H12O6 (glucose) + 6O2 (oxygen) +6H2O (water) Photosynthesis Steps:  During the process of photosynthesis, carbon dioxide enters through the stomata, water is absorbed by the root hairs from the soil and is carried to the leaves through the xylem vessels. Chlorophyll absorbs the light energy from the sun to split water molecules into hydrogen and oxygen.  The hydrogen from water molecules and carbon dioxide absorbed from the air are used in the production of glucose. Furthermore, oxygen is liberated out into the atmosphere through the leaves as a waste product.  Glucose is a source of food for plants that provide energy for growth and development, while the rest is stored in the roots, leaves and fruits, for their later use.  Pigments are other fundamental cellular components of photosynthesis. They are the molecules that impart color and they absorb light at some specific wave length and reflect back the unabsorbed light. All green plants mainly contain chlorophyll a, chlorophyll b and carotenoids which are present in the thylakoids of chloroplasts. It is primarily used to capture light energy. Chlorophyll-a is the main pigment. The process of photosynthesis occurs in two stages:  Light-dependent reaction or light reaction  Light independent reaction or dark reaction Light Reaction of Photosynthesis (or) Light-dependent Reaction  Photosynthesis begins with the light reaction which is carried out only during the day in the presence of sunlight. In plants, the light- dependent reaction takes place in the thylakoid membranes of chloroplasts.  The Grana, membrane-bound sacs like structures present inside the thylakoid functions by gathering light and is called photosystems.  These photosystems have large complexes of pigment and proteins molecules present within the plant cells, which play the primary role during the process of light reactions of photosynthesis.  There are two types of photosystems: photosystem I and photosystem II.  Under the light-dependent reactions, the light energy is converted to ATP and NADPH, which are used in the second phase of photosynthesis.  During the light reactions, ATP and NADPH are generated by two electron-transport chains, water is used and oxygen is produced. The chemical equation in the light reaction of photosynthesis can be reduced to: 2H2O + 2NADP+ + 3ADP + 3Pi → O2 + 2NADPH + 3ATP Dark Reaction of Photosynthesis (or) Light-independent Reaction  Dark reaction is also called carbon-fixing reaction.  It is a light-independent process in which sugar molecules are formed from the water and carbon dioxide molecules.  The dark reaction occurs in the stroma of the chloroplast where they utilize the NADPH and ATP products of the light reaction.  Plants capture the carbon dioxide from the atmosphere through stomata and proceed to the Calvin photosynthesis cycle.  In the Calvin cycle, the ATP and NADPH formed during light reaction drive the reaction and convert 6 molecules of carbon dioxide into one sugar molecule or glucose. The chemical equation for the dark reaction can be reduced to: 3CO2 + 6 NADPH + 5H2O + 9ATP → G3P + 2H+ + 6 NADP+ + 9 ADP + 8 Pi * G3P – glyceraldehyde-3-phosphate Reactions of the Calvin cycle The Calvin cycle reactions can be divided into three main stages: carbon fixation, reduction, and regeneration of the starting molecule. Carbon fixation. A CO2 molecule combines with a five-carbon acceptor molecule, ribulose-1,5-bisphosphate (RuBP). This step makes a six-carbon compound that splits into two molecules of a three-carbon compound, 3-phosphoglyceric acid (3-PGA). This reaction is catalyzed by the enzyme RuBP carboxylase/oxygenase, or rubisco. Reduction. In the second stage, ATP and NADPH are used to convert the 3-PGA molecules into molecules of a three-carbon sugar, glyceraldehyde-3-phosphate (G3P). This stage gets its name because NADPH donates electrons to, or reduces, a three-carbon intermediate to make G3P. Regeneration. Some G3P molecules go to make glucose, while others must be recycled to regenerate the RuBP acceptor. Regeneration requires ATP and involves a complex network of reactions. Glycolysis Glycolysis: is the metabolic pathway that converts glucose into pyruvate. Occurs in the cytosol and is oxygen-independent. The free energy released during the biochemical reactions in glycolysis is used to generate a net gain of two molecules of ATP. Citric Acid Cycle (Kreb’s cycle) The overall reaction of glucose in terms of ADP and ATP is C6H12O6 + 6CO2 + 38 ADP + 38P (inorganic) → 6H2O + 6CO2 + 38 ATP The Krebs cycle or TCA cycle (tricarboxylic acid cycle) or Citric acid cycle is a series of enzyme catalyzed reactions occurring in the mitochondrial matrix, where acetyl-CoA is oxidized to form carbon dioxide and coenzymes are reduced, which generate ATP in the electron transport chain. It is an eight-step process. Krebs cycle or TCA cycle takes place in the matrix of mitochondria under aerobic condition.