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BIOSYNTHESIS OF PURINES AND PYRIMIDINES The DNA and RNA consist of repeating units called Nucleotides , each of which consists of a Purine or Pyrimidine, Pentose (five -carbon sugar), and Phosphate group. Purines (Two ring) and Pyrimidines (One ring) are the nitrogen-containing "bases" found in the nucleotides that make up DNA and RNA. The five-carbon sugars of Nucleotides are derived from either the Pentose phosphate pathway or the Entner - Doudoroff pathway. Certain Amino acids like Aspartic acid, Glycine, and Glutamine - made from intermediates produced during Glycolysis and in the Kreb’s cycle participate in the biosynthesis of Purines (Adenine & Guanine) and Pyrimidines (Cytosine, Thymine & Uracil). The carbon and nitrogen atoms derived from these amino acids form the Purine and Pyrimidine rings, and the energy for synthesis is provided by ATP. DNA contains all the information necessary to determine the specific structures and functions of cells. Both RNA and DNA

BIOSYNTHESIS OF FATTY ACIDS Lipids vary considerably in chemical composition and they are synthesized by a variety of routes. Cells synthesize Fats by joining Glycerol and Fatty acids. The glycerol portion of the fat is derived from Dihydroxyacetone phosphate, an intermediate formed during Glycolysis. Fatty acids, which are long-chain hydrocarbons (hydrogen linked to carbon), are built up when two-carbon fragments of Acetyl CoA are successively added to each other. As with polysaccharide synthesis, the building units of fats and other lipids are linked via dehydration synthesis reactions that require energy, not always in the form of ATP. The most important role of lipids is to serve as structural components of biological membranes, and most membrane lipids are Phospholipids. A lipid of a very different structure, Cholesterol, is also found in plasma membranes of Eukaryotic cells. Waxes are lipids that are important components of the cell wall of Acid-fast bacteria. Other lipids, such

BIOSYNTHESIS AMINO ACIDS Amino acids are organic compounds containing Amine functional group (-NH 2 ) and Carboxyl (COOH) functional groups, along with a side chain(R group). Nutritionally Amino acids are classified into three types. They are 1)     Essential Amino acids 2)     Non-essential Amino acids 3)     Semi-essential Amino acids 1)    Essential Amino Acids (or) Indispensable Amino acids Essential Amino acids are the amino acids which are not synthesized by the body and must be taken in diet. The list of eight Essential amino acids includes: (i) Valine, (ii) Isoleucine, (iii) Leucine, (iv) Lysine, (v) Methionine, (vi) Phenylalanine, (vii) Threonine and (viii) Tryptophan. The dietary importance of Essential Amino Acids was first described by William Cumming Rose. 2)    Non – essential Amino acids (or) Dispensable Amino acids Non-essential Amino acids are the amino acids which are synthesized by the body and must not be taken in diet. The list of ten Non-essent

BIOSYNTHESIS OF CELL WALL POLYSACCHARIDES Microorganisms synthesize Sugars and Polysaccharides. The carbon atoms required to synthesize Glucose are derived from the intermediates produced during processes such as Glycolysis and the Krebs cycle and from lipids or amino acids. After synthesizing Glucose, bacteria may assemble it into more complex polysaccharides, such as Glycogen. For bacteria to build Glucose into glycogen, glucose units must be Phosphorylated and linked.   The product of Glucose phosphorylation is Glucose-6-phosphate.  In order for bacteria to synthesize Glycogen, a molecule of ATP is added to Glucose 6-phosphate to form Adenosine diphosphoglucose (ADPG) . Once ADPG is synthesized, it is linked with similar units to form Glycogen (Polysaccharide). Using a nucleotide called Uridine triphosphate (UTP) as a source of energy and Glucose-6-phosphate, animals synthesize glycogen from Uridine diphosphoglucose (UDPG) . A compound related to UDPG, called UDP-N-acetylglucosamine

  KREB’S CYCLE The Kreb’s cycle (Citric acid cycle or Tricarboxylic acid - TCA cycle) is the most important metabolic pathway for the energy supply to the body. About 65 – 70 % of the ATP is synthesized in Kreb’s cycle. Citric acid cycle essentially involves the oxidation of Acetyl CoA to CO 2 and H 2 O. The name TCA cycle is used, since, at the outset of the cycle, Tricarboxylic acids (Citrate, cis-aconitate and Isocitrate) participate. The Citric acid cycle was proposed by Hans Adolf Krebs in 1937, based on the studies of Oxygen consumption in pigeon breast muscle. The cycle is named in his honour (Nobel Prize for Physiology and Medicine in 1953). The enzymes of TCA cycle are located in Mitochondrial matrix, in close proximity to the Electron transport chain. This enables the synthesis of ATP by Oxidative phosphorylation without any hindrance. The Citric acid cycle is the final common Oxidative pathway for carbohydrates, fats and amino acids. This cycle not only supplies energy but

MICROBIAL RESPIRATION After Glucose has been broken down to Pyruvic acid, the Pyruvic acid can be channeled into the next step of either Fermentation or Cellular respiration. Cellular respiration or simply Respiration, is defined as an ATP - generating process in which molecules are oxidized and the final electron acceptor is (almost always) an inorganic molecule. An essential feature of respiration is the operation of an Electron transport chain. There are two types of respiration. They are (i) Aerobe or Aerobic respiration (which uses oxygen) and (ii) Anaerobe or Anaerobic respiration (which does not use oxygen and may even be killed by it). In Aerobic respiration, the final electron acceptor is O 2 but in Anaerobic respiration, the final electron acceptor is an inorganic molecule other than O 2 or, rarely, an organic molecule Some of the reaction which were carried out under Aerobic respiration are Fermentation, ATP Generation (Substrate level phosphorylation, Oxidative Phosphoryl

ENTNER DOUDOROFF PATHWAY Entner Doudoroff (ED) pathway was discovered by Entner and Doudoroff in 1952 in Pseudomonas saccharophila . ED pathway occurs in both aerobic and anaerobic condition. ED pathway occurs in cytoplasm of prokaryotes only. In the ED pathway, ATP was produced by Substrate level Phosphorylation. Only few bacteria like, Zymomonas mobilis employ the ED pathway. The alcohol productivity of Zymomonas mobilis is higher than yeast because of this fermentative pathway.  Other bacteria using ED pathway are Pseudomonas sp., Azotobacter sp., Rhizobium sp., Agrobacterium sp., Escherichia coli, Enterococcus faecalis, Xanthomonas campestris, Hordeum vulgare and Archaea. ED Pathway Pyruvate and Glyceraldehyde-3-phosphate produced from Glucose by ED pathway. At first Glucose is phosphorylated to Glucose-6-phosphate by the enzyme Hexokinase. Glucose-6-phosphate is then oxidized to 6-Phosphogluconic acid by releasing a molecule of NADPH. This reaction is catalyzed by the enzyme

PHOSPHOKETOLASE PATHWAY Lactic acid is a very common end product of bacterial fermentations. The genera which produce large amounts of lactate are called lactic acid bacteria. Lactic acid fermenters can be separated into two groups. They are (i) Homolactic fermenters and (ii) Heterolactic fermenters. Heterolactic fermenters form substantial amounts of products other than lactate; many produce lactate, ethanol, and CO2 by way of the Phosphoketolase pathway. The heterofermentative bacteria do not use Glycolysis, but use a Phosphoketolase pathway for fermentation. The bacteria Lactobacillus brevis, Lactobacillus fermentum and Leuconostoc sp. are involved in Heterolactic fermentation. In the Phosphoketolase pathway, two ATP and two NADH molecule was produced from Glucose by Substrate level Phosphorylation. In Substrate - Level Phosphorylation, ATP is usually generated when a high-energy Phosphate group is directly transferred from a Phosphorylated compound (a substrate) to ADP. Genera

  GLYCOLYSIS Glycolysis, the oxidation of Glucose to Pyruvic acid, is usually the first stage in Carbohydrate catabolism which takes place in Cytoplasm of the cell. The word Glycolysis means splitting of sugar, and this is exactly what happens (Greek, glycol – sugar; lysis – loosening). Glycolysis pathway was described by Embden, Meyerhof and Parnas in 1940. Hence, it is also called as Embden - Meyerhof pathway. Glycolysis occurs in the absence of oxygen (Anaerobic) or in the presence of oxygen (Aerobic). Lactate is the end product under Anaerobic condition. In the Aerobic condition, Pyruvate is formed, which is then oxidized to CO 2 and H 2 O. The Glycolysis pathway is operated by Yeast to produce Alcohol and Lactic acid bacteria to produce Lactic acid and several Organic acids, gases, Fatty acids and Alcohols. Glycolysis is a major pathway for ATP synthesis in tissues lacking Mitochondria. The enzymes of Glycolysis catalyze the splitting of Glucose (six - carbon sugar) into two

OXIDATIVE PHOSPHORYLATION AND ELECTRON TRANSPORT CHAIN (ETC) OXIDATIVE PHOSPHORYLATION Oxidative phosphorylation is the process in which ATP is formed as a result of the transfer of electrons from NADH or FADH 2  to O 2  by a series of electron carriers. This process, which takes place in mitochondria, is the major source of ATP in aerobic organisms. Oxidative phosphorylation is linked with the Electron transport chain (ETC). ELECTRON TRANSPORT CHAIN Electron transport chain (ETC) is the final common pathway in aerobic cells by which electrons derived from various substrates are transferred to Oxygen. The transfer of electrons from one electron carrier to the next releases energy, some of which is used to generate ATP from ADP through a process called Chemiosmosis. ETC is a series of highly organized Oxidation–Reduction reaction. In Eukaryotes, ETC takes place in the Mitochondria but in Prokaryotes, ETC takes place in Plasma membrane. Carrier Molecules in Electron Transport Chain (