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UNIT III – CELLULAR ENERGY Big Campbell ~ Ch 9, 10 I. ♪ ♫ THE CYCLE OF LIFE ♪ ♫ II. ENERGY IN THE CELL • Catabolic Pathway o Breakdown of molecules that releases stored energy; exergonic rxn o _____________________ – partial breakdown of sugars w/o O2 o ___________________________ – breakdown of sugars w/ O2 o Similar to a car burning gasoline o Although much energy is lost as heat, some can be used to generate ATP by phosphorylating ADP • Oxidation-Reduction Reactions (Redox) o Energy produced in catabolism comes from transfer of eo Movement of e- releases chemical energy of molecule o Released energy is used to attach Pi to ADP to form ATP o 1 molecule loses an e- and a 2nd molecule gains an e- II. ENERGY IN THE CELL, cont • Oxidation-Reduction Reactions, cont o o o o o _________________ – Loss of e_________________ – Gain of e_________________ agent - e- donor _________________ agent - e- acceptor Sometimes there is a complete transfer of e- and other times there is a change in the degree of e- sharing in covalent bonds Inorganic Example: Na + Cl Na+ + Cl- Organic Example: II. ENERGY IN THE CELL, cont • Importance of Electron Carriers o Energy contained in molecules (ex: glucose) must be released in a series of steps Electrons are released as hydrogen atoms with corresponding proton (hydrogen's are “clipped” off) Hydrogen atoms are passed to an _________________ o Electron carriers are coenzymes o “Carry” ______ electrons in the form of H-atoms o Only 1 proton & 2 electrons are delivered o One H+ is released into the surrounding solution o Allow for max energy transfer, minimum energy loss II. ENERGY IN THE CELL, cont • Electron Carriers (oxidative states) _________ e- acceptor in cellular respiration Becomes NADH when reduced Yields about ____ ATP __________ e- acceptor in Krebs Cycle / TCA Cycle / Citric Acid Cycle Yields about ____ ATP __________ e- acceptor in light reaction of photosynthesis Not used in cellular respiration II. ENERGY IN THE CELL, cont • A Closer Look at Electron Carrier Function in Cellular Respiration Reduction of NAD+ o ___________________ oxidizes substrate by removing 2 Hatoms o NAD+ is reduced, creating NADH + H+ o NADH shuttles electrons to __________________________ _________________________. Electrons “fall” down to _______________ in a series of steps, each releasing energy in small amounts. III. CELLULAR RESPIRATION OVERVIEW III. CELLULAR RESPIRATION OVERVIEW, cont’d • Cellular process to convert chemical energy in ___________ (and other molecules) into ________ • Primarily takes place in ___________________ of eukaryotic cells • Overall Reaction ____________________________________________________ • Steps in Cellular Respiration Glycolysis – occurs in cytosol “Splitting of sugar” Initial breakdown of glucose to pyruvate, some ATP Citric Acid Cycle – occurs in mitochondria Completes oxidation of glucose to CO2 Produces ATP, but more importantly provides high-energy electrons for ETC Electron Transport Chain – occurs in mitochondria Oxidative Phosphorylation Highest ATP yield; uses energy released from downhill flow of e- to generate ATP Citric Acid Cycle + Electron Transport Chain = Oxidative Respiration • • • • • IV. GLYCOLYSIS 10 steps Occurs in cytosol of cell Does not require oxygen 1st part of pathway is energy investment phase (5 steps) 2nd part of pathway is energy pay-off phase (5 steps) Energy Investment Phase IV. GLYCOLYSIS, cont Energy Pay-Off Phase IV. GLYCOLYSIS, cont • Summary of Glycolysis V. OXIDATIVE RESPIRATION • 2 pyruvates formed from glycolysis still contain a tremendous amount of chemical energy • If oxygen is available, pyruvate enters mitochondrion for citric acid cycle and further oxidation • Upon entering mitochondrion but prior to entering citric acid cycle o “Grooming” Step Carboxyl group of pyruvate is removed, given off as CO2 Remaining 2-C molecule is oxidized to acetate → NAD+ reduced to NADH + H+ Acetate binds to molecule known as Coenzyme A to form acetyl CoA V. OXIDATIVE RESPIRATION, cont Grooming Step V. OXIDATIVE RESPIRATION, cont • In the citric acid cycle (AKA…Krebs cycle or TCA Cycle), 2 3-carbon molecules go through a series of redox rxns. • Occurs in mitochondrial matrix • Produces NADH, FADH2, ATP, and CO2. • CoA is not actually a part of the reaction . . . it is recycled . . . remember, it is an enzyme! V. OXIDATIVE RESPIRATION, cont V. OXIDATIVE RESPIRATION, cont • Electron Transport – Oxidative Phosphorylation o Traditionally called Electron Transport, now more commonly called ________ ________________________. o Occurs in inner mitochondrial membrane Membrane organized into cristae to ________________ __________________________ o Two components to Oxidative Phosphorylation _________________________ _________________________ V. OXIDATIVE RESPIRATION, cont • Electron Transport Chain Collection of molecules, each more electronegative than the one before it Molecules are reduced, then oxidized as electrons are passed down the chain __________ is ultimate electron acceptor Purpose is to establish H+ gradient on two sides of inner mitochondrial membrane Energy from “falling electrons” used to pump H+ from matrix into intermembrane space V. OXIDATIVE RESPIRATION, cont • Chemiosmosis Enzyme complexes known as _________________ located in inner mitochondrial membrane H+ electrochemical gradient provides energy Known as _________________ Movement of H+ ions through membrane rotates enzyme complex Rotation exposes active sites in complex ATP is produced from ADP and Pi V. OXIDATIVE RESPIRATION, cont • A summary of electron transport . . . VI. CELLULAR RESPIRATION – A SUMMARY • Total ATP Gain in Cellular Respiration = ___ (glycolysis) + ____ (citric acid cycle) + ____ (oxidative phosphorylation) = _____ ATP / glucose VII. CELLULAR RESPIRATION & OTHER FOOD MOLECULES VIII. METABOLIC POISONS • Blockage of Electron Transport Chain • Inhibition of ATP Synthase • “Uncouplers” o Prevent creation of H+ ion gradients due to leakiness of mitochondrial membrane VIII. METABOLIC POISONS, cont IX. FERMENTATION • Anaerobic pathway • Occurs in cytosol • Purpose o In glycolysis, glucose is oxidized to 2 pyruvate, 2 NAD+ are reduced to 2 NADH, and there is a net gain of 2 ATP o In oxidative respiration, NADH is oxidized back to NAD+ in electron transport chain o If oxygen is not present, another mechanism must be available to regenerate NAD+ or glycolysis cannot continue o In fermentation, pyruvate is reduced thereby oxidizing NADH to NAD+ o Allows glycolysis and net gain of 2 ATP per glucose to continue IX. FERMENTATION, cont IX. FERMENTATION, cont