Chapter 5 (Tortora) Microbial Metabolism Chapter 5: Metabolism: Fueling the Cell Growth Metabolism: The sum of all chemical

reactions (anabolic and catabolic) within a living organism. Or An energy balance act. Or YIN-YANG Anabolism or Synthesis: Chemical reactions in which energy is used to synthesize large molecules from simpler components. Example: 1) Amino Acid + Amino Acid H2O 2) Capsule Synthesis in Bacteria Catabolism or Hydrolysis: The chemical breakdown of complex molecules into simpler substances. This process releases energy. 1) Dipeptide H20 2) Breakdown of capsule under unfavorable conditions Enzymes (Organic Catalysts): Proteins produced by living cells that change the rate of a reaction without being consumed by the reaction. Substrate: The substance on which enzyme works. Amino Acid, Amino Acid Dipeptid

 Active or Catalytic Site: The specific portion of an enzyme that attaches to the substrate. Enzyme Structure: A number of enzymes are pure proteins (simple enzymes) however many enzymes (holoenzymes) consist of a protein portion (apoenzyme) and a non-protein portion (coenzyme or cofactor) Coenzyme is an organic molecule such as: Vitamin K Used in electron transport chain Folic Acid Used in the synthesis of nucleic acids

Cofactor is an inorganic ion such as magnesium, zinc, or manganese. The Mechanism of Enzymatic Action 1. The substrate combines with active site of the enzyme. 2. A temporary intermediate compound forms called enzyme-substrate complex. 3. The substrate molecule is transformed by: a. Breakdown of substrate molecule b. Combining two substrate molecule together c. Rearrangement of existing atoms 4. The transformed substrate molecules, now called the product of the reaction, are released from the enzyme molecule. 5. The unaltered enzyme reacts with other substrate molecules. Classification of Enzymes Enzymes can be classified into six categories according to the type of reaction they catalyze. Class 1: Oxidoreductases Catalyze oxidation reduction reactions Example: Cytochrome Oxidase

Class 2: Transferases Move a group (C, N, P or S) from one substrate to another Example: Alanine Deaminase Class 3: Hydrolases Add water to break covalent bonds. Example: Sucrase Class 4: Lyases Break covalent bonds without adding water. Example: Isocitrate Lyase Class 5: Isomerases Rearrangement of atoms within a molecule. Example: Glucose-Phosphate Isomerase Class 6: Ligases Join two molecules to form a larger molecule. Example: DNA-Ligase Location of Enzyme 1. Exoenzymes (extracellular) 2. Endoenzymes (intracellular) Regularity of Enzyme 1. Constitutive Enzymes 2. Inducible (adaptive) Factors Influencing Enzymatic Activity a. Temperature b. pH

c. Substrate Concentration Inhibitors of Enzymatic Activity 1- Competitive Inhibition: A molecule similar to a substrate can bind to an enzymes active site and prevents the formation of end products. Example: Replacement of Para-AminoBenzoic Acid (PABA) with sulfanilamide. Human cells do not make folic acid therefore sulfanilamide selectively kills bacteria. 2- Noncompetitive Inhibition: Substances such as lead and other heavy metals attach to the enzyme at allosteric site and alter the shape of the active site. 3- Feedback Inhibition or End Product Inhibition: The inhibitor (end product) attaches to the allosteric site of the enzyme when it is plentiful and is released when it is in short supply. 4- Enzyme Repression (Genetic Control): End product binds with DNA and stops its production. 5- Enzyme Induction: Enzyme is synthesized only if the inducer (substrate is present). Metabolic Pathways of Energy Production by Heterotrophs Most bacteria are heterotrophs, require prepared organic food to generate energy and are unable to convert inorganic compounds to organic compounds. 1- Aerobic Respiration of CHO 2- Anaerobic Respiration of CHO Aerobic Respiration of Carbohydrates: A process in which carbohydrates are completely oxidized into H2O and energy (ATP). 1. It involves three major steps.

a. Glycolysis b. Krebs cycle c. Electron transport chain 2. Final electron acceptor is almost always an inorganic molecule, most commonly oxygen. Glycolysis 1. Glucose is broken down in a series of reactions to form: 2 molecules of pyruvic acid 4 ATPs (net gain 2 ATP) 2 NADH During a Transition Reaction pyruvic acid is converted into acetyl-CoA, which than enters into krebs cycle. Krebs Cycle or Citric Acid Cycle or Tricarbooxylic Acid Cycle Hydrogen and CO2 are removed at various steps. End products include: 2 4 2 8 ATPs CO2 FADH NADH

Electron Transport Chain (ETC): Accepts hydrogen ions released during previous two steps. End products include: 34 ATP and water ATP Count in Aerobic Respiration: Glycolysis Krebs Cycle ETC Total 4 2 34 40 Net 2 2 34 38

Anaerobic Respiration of Glucose Fermentation (Partial Oxidation) All metabolic processes that release energy from a sugar or other organic molecule, do not require oxygen or an electron transport chain, and use organic molecules as the final electron acceptor. Types of Fermentation: 1. Homolactic/Acidic Fermentation: Glucose Lactic Acid

Examples: Lactobacillus bulgaricus Streptococcus thermophilus 2. Alcoholic Fermentation: Glucose Ethylalcohol+CO2

Example: Sccharomyces cerevisiae Some organisms such as E. Coli can produce both organic acids (lactic, acetic, succinic) and alcohol from glucose and are called heterolactic or heterofermentative bacteria. Photosynthesis in Bacteria On the other hand, some bacteria such as cyanobacteria bacteria (aerobic), green sulfur bacteria, and purple sulfur bacteria (anaerobic) are autotrophs. These bacteria utilize light energy to convert CO2 and H2O (inorganic Compounds) into glucose (organic compound). Photosynthesis involves the following two major steps: A. The light reactions B. The dark reactions The Light Reactions:

1. Cyclic Photophosphorylation (anaerobic organism) End Product: ATP only 2. Noncyclic Photophosphorylation (aerobic organisms) End Products: Oxygen, ATP, and NADPH The Dark Reactions/Calvin-Benson Cycle: Takes place in three stages. 1. The Carboxylation Phase Carbon (from carbon dioxide) is fixed/attached to RuBP (Ribulose 1,5 Biphosphate) to produce PGA (3-Phosphoglyceric Acid). 2. The Reduction Phase Utilizes ATP and NADPH (from light reactions) to produce PGAL (Glyceraldehyde 3-Phosphate). 3. The Regeneration phase PGAL is converted into glucose and RuBP. 6CO2+12H2O+Light C6H12O6+6O2+6H2O End Products of Photosynthesis