Metabolism: The sum of the chemical reactions in an organism A metabolic pathway is a sequence of enzymatically catalyzed chemical reactions in a cell Metabolic pathways are determined by enzymes

Catabolic and Anabolic Reactions Catabolism: Provides energy and building blocks for anabolism. (Break down) Anabolism: Uses energy and building blocks to build large molecules. (Synthesis)

Metabolism: the sum of Catabolism and Anabolism Oxidation: the loss or removal of electrons Reduction: the gain of electrons

Figure 5.1 Role of ATP in Coupling Reactions

Oxidation-Reduction Reactions Oxidation: Removal of electrons Reduction: Gain of electrons Redox reaction: An oxidation reaction paired with a reduction reaction

Oxidation-Reduction Reactions In biological systems, the electrons are often associated with hydrogen atoms. Biological oxidations are often dehydrogenations

The Generation of ATP ATP is generated by the phosphorylation of ADP

Substrate-Level Phosphorylation Energy from the transfer of a high-energy PO 4 – to ADP generates ATP

Oxidative Phosphorylation Energy released from transfer of electrons (oxidation) of one compound to another (reduction) is used to generate ATP in the electron transport chain

Carbohydrate Catabolism The breakdown of carbohydrates to release energy Glycolysis Krebs cycle Electron transport chain

Figure 5.11 Glycolysis The oxidation of glucose to pyruvic acid produces ATP and NADH

Figure 5.12, steps 1–5 Preparatory Stage of Glycolysis 2 ATP are used Glucose is split to form 2 glyceraldehyde-3-phosphate

Figure 5.12, steps 6–10 Energy-Conserving Stage of Glycolysis 2 glucose-3-phosphate oxidized to 2 pyruvic acid 4 ATP produced 2 NADH produced

The Reactions of Glycolysis

The Krebs Cycle Oxidation of acetyl CoA produces NADH and FADH 2

Figure 5.13 The Krebs Cycle

The Reactions of the Krebs Cycle

The Electron Transport Chain A series of carrier molecules that are, in turn, oxidized and reduced as electrons are passed down the chain Energy released can be used to produce ATP by chemiosmosis

Figure 5.11 Overview of Respiration and Fermentation

Figure 5.16 Chemiosmotic Generation of ATP

Figure 5.15 An Overview of Chemiosmosis

A Summary of Respiration Aerobic respiration: The final electron acceptor in the electron transport chain is molecular oxygen (O 2 ). Anaerobic respiration: The final electron acceptor in the electron transport chain is not O 2. Yields less energy than aerobic respiration because only part of the Krebs cycles operates under anaerobic conditions.

Figure 5.16 Respiration

PathwayATP Produced NADH Produced FADH 2 Produced Glycolysis220 Intermediate step020 Krebs cycle262 Total4102 Carbohydrate Catabolism Energy produced from complete oxidation of one glucose using aerobic respiration

Pathway By Substrate-Level Phosphorylation By Oxidative Phosphorylation From NADHFrom FADH Glycolysis260 Intermediate step060 Krebs cycle2184 Total4304 Carbohydrate Catabolism ATP produced from complete oxidation of one glucose using aerobic respiration

Pathway By Substrate-Level Phosphorylation By Oxidative Phosphorylation From NADHFrom FADH Glycolysis260 Intermediate step06 Krebs cycle2184 Total4304 Carbohydrate Catabolism 36 ATPs are produced in eukaryotes

Fermentation One process by which pyruvate is subsequently metabolized in the absence of oxygen The result of the need to recycle the limited amount of NAD by passing the electrons of reduced NAD to other molecules Homolactic acid fermentation: Homolactic acid fermentation: pyruvate is converted directly to lactic acid, using electrons from reduced NAD Alcoholic fermentation: Alcoholic fermentation: carbon dioxide is released from pyruvate to form acetaldehyde, which is reduced to ethanol

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)

Fermentation Scientific definition: Releases energy from oxidation of organic molecules Does not require oxygen Does not use the Krebs cycle or ETC Uses an organic molecule as the final electron acceptor

Figure 5.18a An Overview of Fermentation

Figure 5.19 TypesFermentation Types of Fermentation

Figure 5.27 RequirementsATP Production Requirements of ATP Production

Figure 5.28 A Nutritional Classification of Organisms

Figure 5.28 A Nutritional Classification of Organisms

Figure 5.28 A Nutritional Classification of Organisms

Nutritional TypeEnergy SourceCarbon SourceExample PhotoautotrophLightCO 2 Oxygenic: Cyanobacteria plants Anoxygenic: Green, purple bacteria PhotoheterotrophLightOrganic compounds Green, purple nonsulfur bacteria ChemoautotrophChemicalCO 2 Iron-oxidizing bacteria ChemoheterotrophChemicalOrganic compounds Fermentative bacteria Animals, protozoa, fungi, bacteria. Metabolic Diversity among Organisms