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Chapter 5, part B Microbial Metabolism Overview of Respiration and Fermentation Figure 5.11 Fermentation • Fermentation releases energy from sugars or other organic molecules by oxidation. • Pyruvate is metabolized to various compounds • O2 is not required in fermentation. • Does not use the Krebs cycle or ETC • Electrons removed from the substrate reduce NAD+ to NADH. • The final electron acceptor is an endogenous organic molecule. • Produces only small amounts of ATP (one or two ATP molecules for each molecule of starting material) • ATP molecules are produced by substratelevel phosphorylation. Fermentation • Alcohol fermentation - acetaldehyde is reduced by NADH to produce ethanol. – Product - ethyl alcohol + CO2 (gas) • Lactic acid fermentation (homolactic)pyruvic acid is reduced by NADH to lactic acid. – Product - lactic acid only • Heterolactic fermentation – Product - lactic acid as well as other acids and alcohols. Fermentation Fermentation Figure 5.18b Lipid Catabolism • Lipases hydrolyze lipids into glycerol and fatty acids. (hydrolase) • Fatty acids and other hydrocarbons are catabolized by beta-oxidation. • Catabolic products can be further broken down in glycolysis and the Krebs cycle. Figure 5.20 Protein Catabolism Extracellular proteases Protein Amino acids Deamination, decarboxylation, dehydrogenation Organic acid Urease Urea NH3 + CO2 Krebs cycle Catabolism Highly reduced complex molecules Oxidized NAD+ NADH Energy ADP ATP Metabolic Pathways of Energy Use Anabolism • Polysaccharide Biosynthesis ADPG (adenosine diphosphoglucose). UGPG (uridine diphosphoglucose) UDPNAc ( UDP-N-acetylglucoseamine) Figure 5.28 Metabolic Pathways of Energy Use • Lipid Biosynthesis – Lipids are synthesized from fatty acids and glycerol. • Glycerol is derived from dihydroxyacetone phosphate. • Fatty acids are built from acetyl CoA. Figure 5.29 Metabolic Pathways of Energy Use • Amino Acid and Protein Biosynthesis • All amino acids can be synthesized either directly or indirectly from intermediates of carbohydrate metabolism, particularly from the Krebs cycle. Figure 5.30a Metabolic Pathways of Energy Use • Purine and Pyrimidine Biosynthesis. – The sugars composing nucleotides are derived from either the pentose phosphate pathway or the Entner-Doudoroff pathway. – Carbon and nitrogen atoms from certain amino acids form the backbones of the purines and pyrimidines Figure 5.31 Reversible Reactions • Can readily go in either direction. • Each direction may need special conditions. NADH [Substrate concentration] A + B NAD+ [Product concentration] AB Amphibolic pathways • Anabolic and catabolic reactions are integrated through a group of common intermediates. • Both anabolic and catabolic reactions also share some metabolic pathways, such as Krebs • Such integrated metabolic pathways are referred to as amphibolic pathways. Phototrophs - Photosynthesis • Energy from sunlight is used to convert carbon dioxide( CO2) and water (H2O) into organic materials to be used in cellular functions such as biosynthesis and respiration • Photo: Conversion of light energy into chemical energy (ATP) – Light-dependent (light) reactions • Synthesis: Fixing carbon into organic molecules – Light-independent (dark) reaction, Calvin-Benson cycle • Process is localized in chloroplasts (eukaryotes) or chlorosomes (prokaryotes) Light-dependent (light) reactions Cyclic Photophosphorylation - the electrons return to the chlorophyll Noncyclic photophosphorylation The electrons are used to reduce NADP+ and form NADPH -The electrons from: -H2O or H2S replace those lost from chlorophyll (H2S) (S) Figure 5.24a Photosynthesis • Oxygenic: 6CO2 + 12H2O + Light energy C6H12O6 + 6 O2 + 6H2O • Anoxygenic: 6CO2 + 12H2S + Light energy C6H12O6 + 12 S + 6 H2O Light-independent (dark) reaction • Photosynthesis: Fixing carbon (CO2) into organic molecules • • Calvin-Benson cycle • Use NADPH as cofactor • Characteristic of: - Cianobacteria, - Green and Purple bacteria - Algae and Plants Autotrophs: Carbon dioxide (CO2) is used as source of carbon Figure 5.25 A Summary of Energy Production Mechanisms Nutritional types of organisms by Sources of energy Chemotrophs: Bond energy is released from a chemical compound Phototrophs: Light is absorbed in photo receptors and transformed into chemical energy. Chemoheterotrophs • Chemotrophs - Organisms that use energy from organic chemicals Glucose NAD+ ETC Pyruvic acid NADH ADP + P ATP • Heterotrophs: Organic compounds are metabolized to get carbon for growth and development. • Cannot fix carbon Chemoautotrophs • Use energy from inorganic chemicals • Energy is used in the Calvin-Benson cycle to fix CO2 2Fe2+ NAD+ ETC 2Fe3+ NADH 2 H+ • Chemoautotroph – Thiobacillus ferrooxidans ADP + P ATP Phototrophs • Use Energy from sunlight Chlorophyll ETC Chlorophyll oxidized ADP + P ATP • Energy is used in the Calvin-Benson cycle to fix CO2 – Photoautotrophs • Energy is used in anabolism (carbon from organic compounds) Photoheterotrophs A nutritional classification of organisms Metabolic Diversity Among Organisms Nutritional type Energy source Carbon source Example Photoautotroph Light CO2 Oxygenic: Cyanobacteria plants. Anoxygenic: Green, purple bacteria. Green, purple nonsulfur bacteria. Photoheterotroph Light Organic compounds Chemoautotroph Chemical CO2 Iron-oxidizing bacteria. Chemoheterotroph Chemical Organic compounds Fermentative bacteria. Animals, protozoa, fungi, bacteria. Carbon cycle Sulphur cycle Nitrogen cycle Phosphorus cycle Biochemical tests and bacterial identification Staphylococcus aureus Pseudomonas aeruginosa Gram stain Bacillus subtilis Kelbsiella pneumonia • K. pneumonia and Ps. aeruginosa look alike through a microscope after Gram stain; so how can they be differentiated? Different species produce different enzymes determine what type of metabolic reactions an organism can carry out – Oxygen requirements – Fermentation of different substrates (sugars) – Enzymes of respiration – Amino acid catabolizing enzymes Toxic Forms of Oxygen • Singlet oxygen: O2 boosted to a higher-energy state • Superoxide free radicals: O2– • Peroxide anion: O22– • Hydroxyl radical (OH) Chemical Requirements Oxygen (O2) Fermentation test Protein Catabolism •Fermentation tests are used to determine the substrates the organism can metabolize by the products it generates. E.coli Control tube S.epidermidis S.aureus Medium: Carbohydrate Mannitol, inverted Durham tube Products: Acid and gas. . Figure 5.23 Protein Catabolism Urease NH3 + CO2 Dichotomous Key • A dichotomous key is a series of questions which leads to the identification of an item. – a device on paper or computer that aids identification of a species or other type of entity. • Dichotomous keys are used for the identification of organisms. • A dichotomous key works by offering two alternatives at each juncture, and the choice of one of those alternatives determines the next step. Learning objectives • Describe the chemical reactions of, and list some products of, fermentation. • Describe how lipids and proteins undergo catabolism. • Provide two examples of the use of biochemical tests to identify bacteria. • Compare and contrast cyclic and noncyclic photophosphorylation. • Compare and contrast the light-dependent and light-independent reactions of photosynthesis. • Compare and contrast oxidative phosphorylation and photophosphorylation. • Write a sentence to summarize energy production in cells. • Categorize the various nutritional patterns among organisms according to carbon source and mechanisms of carbohydrate catabolism and ATP generation. • Describe the major types of anabolism and their relationship to catabolism. • Define amphibolic pathways