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Chapter 06 Metabolism: Fueling Cell Growth Two fundamental tasks needed to grow. Synthesis of macromolecules Metabolism Important to humans Food, medicine, energy, research Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 A Glimpse of History Biologists had noticed that in vats of grape juice, alcohol and CO2 are produced while yeast cells increase in number Biologists concluded that multiplying cells were converting sugar in the juice to alcohol and CO2 But idea not widely accepted • Mocked by influential chemists and others In 1850s, Louis Pasteur set out to determine how alcohol develops from grape juice • Simplified setup: clear solution of sugar, ammonia, mineral salts, trace elements • Added a few yeast cells—as they grew, sugar decreased, alcohol level increased • Strongly supported idea, but Pasteur failed to extract something from inside the cells that would convert sugar In 1897, Eduard Buchner, a German chemist, showed that crushed yeast cells could convert sugar to ethanol and CO2; awarded Nobel Prize in 1907 • Enzymes were extracted….. Microbial Metabolism All cells need to accomplish two fundamental tasks 1) Synthesize new parts • Cell walls, membranes, ribosomes, nucleic acids 2) Harvest energy to power reactions • Sum total of these is called metabolism • Human implications • • • • • Used to make biofuels Used to produce food Important in laboratory Invaluable models for study Unique pathways potential drug targets 6.1. Principles of Metabolism Can separate metabolism into two parts 1) Catabolism • Processes that degrade compounds to release energy • Cells capture to make ATP 2) Anabolism/Biosynthesis • Biosynthetic processes • Assemble subunits of macromolecules • Use ATP to drive reactions • Processes intimately linked Harvesting Energy Energy is the capacity to do work Two types of energy 1) Potential: stored energy (e.g., chemical bonds, rock on hill, water behind dam) 2) Kinetic: energy of movement (e.g., moving water) Energy in universe cannot be created or destroyed, but it can be converted between forms Harvesting Energy Photosynthetic organisms harvest energy in sunlight • Power synthesis of organic compounds from CO2 • Convert kinetic energy of photons to potential energy of chemical bonds Chemoorganotrophs obtain energy from organic compounds • Depend on activities of photosynthetic organisms Harvesting Energy Free energy - is energy available to do work after a chemical reaction has occured • E.g., energy released when chemical bond is broken • Compare free energy of reactants to free energy of products 1)Exergonic reactions: reactants have more free energy • Energy is released in reaction 2)Endergonic reactions: products have more free energy • Reaction requires input of energy Components of Metabolic Pathways Role of Enzymes (Proteins) – suffix “ase”… • Biological catalysts: accelerate conversion of substrate into product by lowering activation energy • Highly specific: one at each step • Reactions would occur without, but extremely slowly Components of Metabolic Pathways Role of ATP • Adenosine triphospate (ATP) is energy currency • Composed of ribose, adenine, three phosphate groups • Adenosine diphospate (ADP) acceptor of free energy • Cells produce ATP by adding Pi to ADP using energy • Release energy from ATP to yield ADP and Pi Precursor Metabolites Precursor metabolites are intermediates of catabolism that can be used in anabolism • Serve as carbon skeletons for building macromolecules • E.g., pyruvate can be converted into amino acids alanine, leucine, or valine 6.2. Enzymes Environmental Factors Influencing Enzyme Activity • Enzymes have narrow range of optimal conditions • Temperature, pH, salt concentration • 10°C increase doubles speed of enzymatic reaction up until maximum • Proteins denature at higher temperatures • Low salt, neutral pH usually optimal 6.5. Fermentation Fermentation end products varied; helpful in identification, commercially useful • E. coli is facultative anaerobe • Lactic acid • Ethanol • Aerobic respiration, anaerobic respiration, and fermentation • Butyric acid • Propionic acid • Streptococcus pneumoniae • 2,3-Butanediol • Fermentation only option • Mixed acids Fermentation used when respiration not an option 6.8. Photosynthesis Photosynthesis • Plants, algae, several groups of bacteria • General reaction is Light Energy 6 CO2 + 12 H2X C6H12O6 + 12 X + 6 H2O where X indicates element such as oxygen or sulfur • Can be considered in two distinct stages • Light reactions (light-dependent reactions) – Capture energy and convert it to ATP • Light-independent reactions (dark reactions) – Use ATP to synthesize organic compounds – Involves carbon fixation Chapter 06 Metabolism: Fueling Cell Growth Two fundamental tasks needed to grow. Synthesis of macromolecules Metabolism Important to humans Food, medicine, energy, research Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14