Micro Bio February 10, 2010 Metabolism Definition: sum of cellular bio chemical reactions Comprises: Catabolism: breakdown of complex molecules to simpler products. In many cases, results in energy production in form of NAD(P)H, ATP and heat. ATP and reductants used drive anabolic reactions. Anabolism: synthesis of complex macromolecules and cells from simpler precursors. This is BIOSYNTHESIS and Requires energy input. There are few reversible metabolic pathways some that can function ana-and catabolically knoan as AMPHIBOLIC PATHWAYS, E.g some stems in Glycolysis and Krebs Cycle Catebolism (13.12) Catabolite: substrate for Catabolic Reaction Two Main functions: Oxidation to produce energy. Breakdown of macromolecules to provide smaller building blocks for bio synthesis. Oxidation of Glucose Complete oxidation takes place in three steps Conversion of glucose to pyruvic Acid (Pyruvate) Krebs or Tricarboxylic Acid (TCA) cycle Oxidative Phosphorylation Conversion to Glucose to Pyruvate (13.15) 3 main pathways in microbes- all anaerobic Glyclosis emden-Meryhoff-parnas [epm] pathway Pentose Phosphate Pathway/Shunt Enter-Doudoroff Pathway 1. Glycolysis (13.17) - Many Pathway for glucose breakdown - Sugars other than glucose also feed into this pathway by conversion to one of its intermediates. - 2 stages involved: a. (during) 6-Carbon stage- ATP is consumed b. 3- carbon stage- ATP, NADH generated. ATP in this stage produced via substrate level Phosphorylation (slp) Glucose +2ADP+2NAD 2 Pyr+2ATP+2NADH Note the many amphibolic reactions in this pathway. 2. Pentose Phosphate Pathway (13.20) - Generally, more important for biosynthesis than energy production- provides main reductant used in biosynthesis, NADPH - provides 3C-7C sugars: very useful Substrates for Biosynthesis, e.g 4C sugars for aromatic Amino Acids, 5C sugars for Dna/RNA - However, also produces ATP via Conversion of Glyceraldehyde-3 phosphate to pyruvate (see glyclosis) - Key Enzymes: Transketolase Transaldoase 3. Entner- Doudoroff pathway (13.19) - used in place of glycolysis in many microbes - Produces one ATP, one NADH and One NADPH b. The TCA Cycle (13.24) Involves: Oxidation of pyruvate to CO2 and H2O Key substrate- Acetyl Coenzyme A, Derived from decarboxylation of pyruvate by pyruvate dehydrogenase. The TCA cycle is an INDIRECT source of large amounts of ATP (see oxid. Phos) For Each AcCoA, it generates: 1 FADH 3 NADH 1 GTP or ATP by SLP 2 CO2 Also provides carbon skeletons for biosynthesis C. Oxidative Phosphorylation (14.15) - An electron transport chain accepts electrons from NADH and FADH2 - When electrons transferred to O2 as final accecptor, process is AREOBIC RESPIRATION. If compound other than O2, known as ANAEROBIC RESPIRATION. - Energy is relaeased in the process of electron transport (movement from redox couple with negative EO to one that is more Positive; Table 14.1) - This energy is used to pump protons across the membrane to generate a Proton Potiential or Proton Motive Force (PMF) - The PMF cand be used to do work, including ATP synthesis using membrane-bound ATP synthase complex (Fig 14.19) ? Inner membrane of bacteria, cristae of mitochondria (inner membrane) - This configuration process is known as oxidative phosphorylation - In ecaryotes, each NADH generates~ 3 ATP via aerobic respiration; FADH2 Thus, the electron transport chain required to provide most of the energy (ATP) derived from oxidation of glucose. Fermentations (13.21) Generate lots of incompletely oxidized waste products that are exerted from cell. Pyruvate does not feed in to TCA cycle. NADH from glyclosys, etc, not oxidized by electron transport chain; thus is a low energy process. This represents a problem: how to regenerate NAD from NADH (if NAD not regenerated, the whole process stops=death) NADH oxidized by an organic molecule such as pyruvate or one of its derivatives. Thus, in fermentation reactions, organic molecules serve as e- Donors and Acceptors These reactions also yield a wide range of products (alcohols, acids, aldehydes, etc)- have food and industrial applications and also serve as a diagnostic method for identification of the enteric bacteria (13.23)
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