Ch 5 Microbial Metabolism Objectives Differentiate between anabolism

Ch 5 Microbial Metabolism

Objectives: Differentiate between, anabolism, and catabolism. Identify the components of an enzyme and describe the mechanism of enzymatic action. List the factors that influence enzymatic activity. Explain what is meant by oxidation–reduction. Describe the chemical reactions of glycolysis. Explain the products of the Krebs cycle. Describe the chemiosmotic model for ATP generation. Compare and contrast aerobic and anaerobic respiration. Describe the chemical reactions and some products of fermentation. Categorize the various nutritional patterns among organisms according to energy and carbon source.

Catabolic and Anabolic Reactions • Metabolism: The sum of all chemical reactions in an organism • Catabolism: Provides energy and building blocks for anabolism. • Anabolism: Uses energy and building blocks to build large molecules

Role of ATP in Coupling Reactions A metabolic pathway is a sequence of enzymatically catalyzed chemical reactions in a cell. Metabolic pathways are determined by enzymes, which are encoded by genes. Fig 5. 1

Collision Theory • states that chemical reactions can occur when atoms, ions, and molecules collide • Activation energy is needed to disrupt electronic configurations • Reaction rate is the frequency of collisions with enough energy to bring about a reaction. • Reaction rate can be increased by enzymes or by increasing temperature or pressure

Enzymes lower Activation Energy Compare to Fig 5. 2

Fig 5. 3 Enzymes • Biological catalysts; specific; not used up in that reaction • Enzyme components: – Apoenzymes, Cofactors, Holoenzymes – Coenzymes (NAD+, NADP+, FAD) • Naming of enzymes (see Table 5. 1): Lactate dehydrogenase; Cytochrome oxidase; ligase, transferase etc.

Mechanism of Enzymatic Reactions Compare to Fig 5. 4

Factors Influencing Enzyme Activity Enzymes can be denatured by temperature and p. H Fig 5. 5 c Fig 5. 6 Substrate concentration influencing enzyme activity

Inhibitors Noncompetitive – Competitive vs allosteric inhibitors Fig 5. 7

Sulfa drugs

Feedback Inhibition Also known as endproduct inhibition Controls amount of substance produced by a cell Mechanism is allosteric inhibition Fig 5. 8

Energy Production: Oxidation-Reduction Reactions • Oxidation = removal of e • Reduction = gain of e - - Redox reaction = oxidation reaction paired with reduction reaction. Fig 5. 9

Oxidation-Reduction cont. In biological systems, the electrons are often associated with hydrogen atoms. Biological oxidations are often dehydrogenations. Fig 5. 10

The Generation of Phosphorylation: ATP 1. Substrate level phosphorylation: transfer of a highenergy PO 4– to ADP. 2. Oxidative phosphorylation: transfer of electrons from one compound to another is used to generate ATP by chemiosmosis.

Metabolic Pathways of Energy Production: COH Catabolism • Cellular respiration – Aerobic respiration – Anaerobic respiration • Fermentation The three steps of aerobic respiration 1. Glycolysis (oxidation of _____ to ______) 2. Krebs cycle (oxidation of acetyl Co. A to ___) 3. Oxidative phosphorylation (e- transport chain)

Glycolysis Multi – step breakdown of glucose into pyruvate Generates • small amount of ATP (how many? ) • small amount of reducing power – (? ) • Alternative pathways: Pentose phosphate and Entner-Doudoroff

The Steps of Glycolysis Compare to Fig. 5. 12

• Other names? Krebs Cycle • Transition step generates acetyl-Co. A from pyruvate (decarboxylation) • Acetyl group of acetyl. Co. A enters TCA cycle • Generates ATP and reducing power • Generates precursor metabolites

Krebs Cycle Compare to Fig 5. 13

Electron Transport Chain • Formed by series of electron carriers (cytochromes) located in ______ • Oxidation/Reduction reactions. Electron carriers (reducing power) from glycolysis and TCA cycle transfer their electrons to the electron transport chain • Generates proton gradient or proton motive force (pmf) • In chemiosmosis, pmf generates energy via oxidative phosphorylation

Electron Transport and the Chemiosmotic Generation of ATP Fig. 5. 16

Overview of Respiration and Fermentation Foundation Figure Fig 5. 11

Fig 5. 17

Anaerobic Respiration • Inorganic molecule is final electron acceptor, e. g. : – NO 3 - – SO 42 - • ATP yield lower than in aerobic respiration because only part of Krebs cycle operates under anaerobic conditions.

Fermentation • Any spoilage of food by microorganisms (general use) • Any process that produces alcoholic beverages or acidic dairy products (general use) • Any large-scale microbial process occurring with or without air (common definition used in industry) Scientific definition: • Uses an organic molecule as the final electron acceptor • Does not use the Krebs cycle or ETC • Energy yield low (see Table 5. 4) • Diversity of end products: ___________

The Relationship of Fermentation to Glycolysis Not in book Also view Fig 5. 18

Location of Carbohydrate Catabolism Pathway Glycolysis Intermediate step Krebs cycle ETC Eukaryote Prokaryote

Energy produced from complete oxidation of one glucose molecule using aerobic respiration Pathway Glycolysis Intermediate step Krebs cycle Total ATP Produced NADH Produced FADH 2 Produced

ATP produced from complete oxidation of one glucose using aerobic respiration Pathway Glycolysis Intermediate step Krebs cycle Total By Substrate-Level Phosphorylation By Oxidative Phosphorylation From NADH From FADH

Carbohydrate Catabolism • 36 ATPs are produced in eukaryotes Pathway By Substrate-Level Phosphorylation By Oxidative Phosphorylation From NADH From FADH 0 Glycolysis 2 6 Intermediate step 0 6 Krebs cycle 2 18 4 Total 4 30 4

Catabolism of Other Compounds • Polysaccharides and disaccharides – Amylases for digestion of ______ (very common) –Cellulase for digestion of cellulose (only bacteria and fungi have this enzyme) – Disaccharidases • Lipid catabolism not covered

Protein Catabolism Protein Extracellular proteases Deamination, decarboxylation, dehydrogenation, desulfurylation Amino acids Organic acid Decarboxylation Krebs cycle

Biochemical Tests and Bacterial Identification: Fermentation Tests Different species produce different enzymes test detects enzyme Mannitol Fermentation:

Metabolic Diversity among Organisms • Energy source: Phototrophs vs. Chemotrophs • Principal carbon source: Autotrophs vs. Heterotrophs • Chemoheterotrophs use same organic compound as energy source and carbon source. Most medically important bacteria. • Saprophytes vs. parasites

Anabolic Pathways Biosynthesis not covered, except for Protein biosynthesis (see Ch 8)