CHAPTER 5 MICROBIAL METABOLISM I. Catabolic and Anabolic Reactions A. Metabolism - The sum of all chemical reactions within a living cell either releasing or requiring energy. (Overhead) Fig 5.1 1. Catabolism - Breaking down complex organic compounds into simpler ones. a) Usually release energy b) Released energy is transferred to and trapped in ATP. Some is given off as heat. c) Released energy is used to drive anabolic reactions 2. Anabolism- The building of complex organic molecules from simpler ones. a) For example: Formation of proteins from amino acids, nucleic acids from nucleotides, polysaccharides from simple sugars. These materials are used for cell growth. b) Reactions usually require energy from ATP. II. Enzymes Overhead Fig 5.4 A. Descriptions 1. Proteins produced by living cells that that use them to catalyze chemical reactions. 2. Names usually end in -ase 3. When enzyme and substrate combine, substrate is transformed and enzyme is recovered. Fig 5.4 4. Operate at optimum temperature and ph fig 5.5a,b,c fig 5.6 5. Reaction is often controlled by feedback inhibition - End product inhibits an enzyme s activity somewhere in the pathway. Fig 5.8 Microbiology 8 Chapter5taft 1
III. Energy Production A. Oxidation-Reduction with transfer of energy 1. Oxidation is removing electrons; Reduction is gaining. Fig 5.9 2. Each time a substance is oxidized another is reduced. 3. Most biological oxidation is by loss of hydrogen atoms (H+ and e-), so is called dehydrogenation reaction. Fig 5.10 Example: NAD+ is the oxidized form; NADH is the reduced form (overhead). NADH used to capture and transfer energy. 4. Energy is released during a cell s oxidation of glucose as hydrogens are removed. B. Generation of Adenosine Triphosphate (ATP) for Energy Storage (see chapter fig 2.18) 1. ADP traps energy released by certain metabolic reactions (especially catabolism of glucose) to form ATP. Stored as ATP until needed. IV. Biochemical Pathways of Energy Production A. Description: Series of enzymatically catalyzed reactions called biochemical pathways store energy in and release energy from organic molecules. Ex.: Fig 5.12 Appendix C fig C.2 B. Carbohydrate Metabolism 1. Most of a cell s energy is produced from the oxidation of carbohydrate - Most commonly glucose 2. Two major types of glucose catabolism are: Fig 5.11 a) Respiration, in which glucose is completely broken down to CO 2 and H 2 0 creating much ATP. The final electron acceptor in this oxidation is usually 0 2, but may be other inorganic ions. This happens in the mitochondria of eukaryotes. b) Fermentation in which it is partially broken down producing small amounts of ATP and using no 0 2. Microbiology 8 Chapter5taft 2
3. A common pathway to both respiration and fermentation is glycolysis (there are alternate pathways). Glucose (6 carbons) is oxidized (using no 0 2 ) to 2 pyruvic acids (3 carbons) with production of some ATP and energy containing NADH. Fig 5.11, fig 5.12 4. Respiration using 0 2 is called aerobic respiration. Fig 5.11 Once glycolysis is completed and pyruvic acid is made two other metabolic pathways are used sequentially: the Krebs cycle and, the electron transport chain (ETC) a) Krebs cycle is the oxidation of a derivative of pyruvate (acetyl CoA) to CO 2 with production of some ATP, and energy containing NADH and FADH 2. 2 ATP are produced. fig 5.13, Appendix C5. b) Electron transport chain where NADH and FADH2 are oxidized and give up their electrons to a series of carrier molecules in a membrane. As the electrons come off the last carrier they combine with O 2 and H+ to form H 2 O water. Fig 5.14 Energy is released in a stepwise manner to produce a considerable amount of ATP (34 from 1 glucose). Notice that the ATP is produced as H+ moves thru a special protein channel in the membrane. Fig 5.15, fig 5.16. c) Summary of respiration. Fig 5.17. Table 5.3. Large amounts of ATP made, O 2 used as final electron acceptor, CO 2 and H 2 O are wastes products. 5. Respiration without 0 2 is called anaerobic respiration. a) anaerobic - inorganic molecule other than O 2. Table 5.5 p 135. b) Example: Some bacteria such as Pseudomonas and Bacillus can use nitrate ion (NO3-) as final electron acceptor. Since not all the carriers in the ETC participate in anaerobic respiration, the amount of ATP produced is never as much as aerobic respiration but still much better than fermentation. 6. Fermentation the pyruvate made during glycolysis is converted to an organic product. Fig 5.18 a) Releases energy from sugars or other organic molecules by oxidation. Only 2 ATP produced per glucose molecule. Does not use the Krebs cycle or the ETC. Microbiology 8 Chapter5taft 3
b) O 2 is not required in fermentation c) Final electron acceptor is an organic molecule d) Examples :Two end products can be alcohol or lactic acid. Fig 5.19, Table 5.4 p135. 7. Biochemical Tests - C. Photosynthesis a) Bacteria and yeasts can be identified by detecting the action of their enzymes on substrates. b) Fermentation tests are used to determine whether an organism can ferment a carbohydrate to produce acid and gas. 1. 6 CO 2 + 12 H 2 O + light energy C 6 H 12 O 6 + 6O 2 + 6H 2 O 2. Converts light energy from the sun into chemical energy. Fig 5.24 a) Light dependent- Photophosphorylation (1) Cyclic- Electrons return to chlorophyll (2) Non-cyclic- Electron are incorporated into NADPH and products are ATP & O 2 (3) Cyanobacteria and algae Microbiology 8 Chapter5taft 4
3. Dark reaction- Electrons from light dependent + energy from ATP reduce CO 2 to sugar. D. Other Catabolic Reactions 1. Lipid - Lipases hydrolyze lipids into glycerol and fatty acids. Glycerol and the fatty acids are then broken down in the Krebs cycle. 2. Protein Proteins are broken down by proteases and peptidases to amino acids that are converted to various substances that enter the Krebs cycle. a) Amino acid is deaminated where an NH 2 is removed so it can enter the Krebs cycle. b) Also maybe decarboxylated where COOH is removed. V. Biochemical Pathways of Energy Use (Anabolism) A. Biosynthesis = production of new cellular components from simple molecules. Examples: 1. Polysaccharides - Glycogen and basic material for peptidoglycan. Fig 5.28. 2. Lipids -Made from glycerol (produced during glycolysis) and fatty acids (produced from acetyl CoA during preparatory step for the Krebs cycle). Fig 5.29. 3. Purines and pyrimidines are part of the nucleotide subunits needed to make DNA and RNA. Amino acids made from intermediates of glycolysis and the Krebs cycle participate in the synthesis of purines and pyrimidines. Fig 5.31 VI. Metabolic Diversity Among Organisms A. Nutritional Classification by energy and carbon source - Figure 5.27 1. Energy a) Phototrophs - Use light as their primary energy source b) Chemotrophs - Depend upon oxidation-reduction reactions of inorganic or organic compounds for energy. Microbiology 8 Chapter5taft 5
2. Carbon Source a) Autotrophs - Use carbon dioxide b) Heterotrophs - Require an organic carbon source 3. Combination a) Photoautotrophs b) Photohererotrophs c) Chemoautotrophs d) Chemoheterotrophs - Most medically important organisms are in this group. Microbiology 8 Chapter5taft 6