ESSENTIAL CONCEPTS OF METABOLISM CHAPTER 5

Metabolism Anabolism Small molecules joined by bonds Energy required Catabolism Bonds broken, Energy released

Microbial Metabolism Autotrophy versus heterotrophy Chemo- versus Photo-

Energy Capture Electron Transfer Redox Reactions

Enzymes Control Metabolic Pathways Proteins Catalysts Activation Energy lowered Apoenzyme Holoenzyme Active Site

Apoenzyme versus Holoenzyme Coenzyme Cofactor Holoenzyme

Enzyme/Substrate Complex – a highly specific binding event which allows new product(s) to be formed.

Enzyme Inhibition Competitive

Enzyme Inhibition Noncompetitive Allosteric site Feedback Inhibition

Reaction Rate Influences Temperature pH

Effect of Enzyme Concentration

Effect of Substrate Concentration Product Concentration – Often a regulatory role

Carbohydrate Catabolism Universal First Step – Glycolysis Pathway Overall reaction: Glucose + 2 ATP + 2ADP + 2 Pi + 2 NAD+ 2 Pyruvate + 4 ATP + 2NADH* Low Energy Yield in terms of ATP (2 ATP) *NADH molecules carry large quantities of energy Not always available to the cell

Glycolytic Pathway Each step is a separate enzymatic reaction

High Energy Electron-Carrying Coenzymes Nicotinamide Adenine Dinucleotide NAD+ + H+ + 2e– NADH Flavin Adenine Dinucleotide FAD + 2H+ + 2e– FADH2

Fermentation Follows Glycolysis in some microbes Anaerobic process Substrate : 2 Pyruvate molecules per glucose End products of reduction: Acids (Lactobacillus) Alcohols (Saccharomyces) Re-oxidizes 2 NADH to allow NAD+ usage in glycolysis No ATP created during fermentation

Acid/Alcohol Fermentation Pathways

Aerobic Respiration Alternative to Fermentation possessed by some microbes Aerobic process 2 Pathways combined Krebs Cycle Electron Transport Chain

Krebs Cycle Needs Acetyl Coenzyme A Preparatory Step: 2 Pyruvate + 2 NAD+ + 2 CoenzymeA 2 CO2 + 2 Acetyl CoA + 2 NADH

Krebs Cycle Pathway Krebs Cycle oxidizes remaining organic carbon molecules to CO2 Oxidative Phosphorylation (Electron Transport Chain) harnesses the energy within reduced NADH and FADH2 Allows extraction of energy from NADH and other high energy electron carriers

Krebs Cycle Oxidation Substrates: 2 Acetyl CoA per original glucose molecule 2 GDP (ADP equivalents) 6 NAD+ 2 FAD Products: 4 CO2 2 GTP (ATP equivalents) 6 NADH 2 FADH2

Electron Transport Chain Redox Electrons from NADH and FADH2 Electron Carriers Flavoproteins Cytochromes Ubiquinones Terminal electron Acceptor Oxygen atom Reduced to water

Electron Transport Chain (ETC) Energy Yields

Electron Transport Chain - Molecular Events

Chemiosmosis

Energy Yields Glycolysis: 2 ATP Substrate level phosphorylation Krebs Cycle: 2 ATP Electron Transport Chain: 34 ATP 10 NADH yield 30 ATP 2 FADH2 yield 4 ATP Oxidative phosphorylation Aerobic Respiration total: 36 ATP Glycolysis + Aerobic Respiration total: 38 ATP

Anaerobic Respiration Respiration Pathway (Krebs Cycle + ETC) using inorganic terminal e– acceptors other than O2 Energy yield is less than Aerobic Respiration but greater than fermentation

Fat Catabolism Glycerol Enters glycolysis Fatty Acids Beta oxidation creates Acetyl coA Enters the Krebs cycle

Protein Catabolism Protein hydrolysis Deamination NH2 group is lost Carbon skeleton usage Krebs cycle Some to glycolysis

Photosynthesis (1) Light dependent reactions - Photophosphorylation

Photosynthesis (2) Light independent reactions Carbon fixation ATP provides energy to link carbon atoms into glucose molecules Water conservation is an issue for many plants

Energy Usage Biosynthesis (Anabolism) Membrane Transport Motility Bioluminescence