Cellular Metabolism Cellular Respiration PDF

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Cellular Metabolism: Cellular Respiration Endergonic Reactions and Energetic Coupling - Endergonic reactions need a continue input of energy to process - Energetic coupling between an exergonic and endergonic reactions Adenosine Triphosphate Hydrolysis - Endergonic reactions/processes coupled to the hydrolysis of ATP ★ ATP’s clustered negative charges give it high potential energy ★ Hydrolysis of a phosphate group leads to a drop in potential energy ★ Coupled to an edergonic process/reaction Cells Need Energy For Work: - Energy storage: fats and polysaccharies - Converted to ATP as needed through a series of tightly controlled REDOX reactions where glucose is becoming oxidized

REDOX Reactions

Aerobic Cellular Respiration 1) Oxidation of glucose 2) Most ATP produced in Step 4

Electrons not given directly to oxygen from glucose but are brought to an oxygen containing step by electron carriers:

Glycolysis - Splotting of Glucose into 2 pyruvate molecules - Occurs in the cytoplasm and has multiple reactions divided into investment and payoff phases Investment Phase - Glucose splits into 2 molecules of G3P - 2 molecules of ATP are added (invested) - When the phosphate groups are transferred to the reactants, this raises their energy level (activation) Payoff Phase

Summary of Glycolysis - Starting Reactant: Glucose - Location: Cytoplasm - Invested: 2 ATP and 2 Pi - Output of Reaction: 4 ATP (overall net gain of 2 ATP), 2 NAD+ reduced to 2 NADH and 2 molecules of pyruvate - Regulated by Phosphofructinase and negative feedback regulation: High levels of ATP inhibits Phosphofructinase ★ Allosteric Enzyme Inhibitor: Enzymes transfers phosphate groups from ATP to an intermediate of Glycolysis

The process of the oxidizing glucose has begun but most of the potential energy to be harvested still remains in the 2 molecules of pyruvate. The 2 molecules of NADH will go to the 4th step of aerobic cellular respiration (electron transport chain) - ATP is produced through substrate level phosphorylation - Glycosis → ADP = ATP Pyruvate Processing - Occurs in the Mitochondrial matrix - Ocurs in a large enzyme complex: Pyruvate dehydrogenase - which shuts down with high levels of acetyl CoA and NADH aka NEGATIVE FEEDBACK INHIBITION Summary of Pyruvate Processing - Starting Reactant: 2 molecules of pyruvate - Location of Reaction: mitochondrial matrix - Added to Reaction: 2 molecules of Coenzyme A (CoA) - Output of the reaction: 2 molecules of carbon dioxide, 2 NAD+ gain electrons forming 2NADH, 2 moles of Acetyl CoA and NO ATP - Continue oxidizng the breakdown products of glucose, most of the potentiale energy to be harvested is still within the acetyl groups Citric Acid Cycle - Occurs in the mitochondrial matrix - Reduction of 8 electron carriers (per glucose): 6NADH and 2FADH2 - 2 ATP produced per glucose via substrate level phosphorylation - Complete oxidation of breakdown products of glucose: all possible potential energy is harvested as high energy electrons

Summary of Citric Acid Cycle - Krebs Cycle - Starting Reactants: 2 Molecules of Acetyl CoA - Location: mitochondrial Matrix - Output of Reaction: 4 molecules of carbon dioxide, 2 molecules of ATP, 6 NAD+ becomes reduced forming 6 NADH, 2 FAD becomes reduced forming 2 FADH2 - All high energy electrons have been harvested from glucose (glucose is completely oxidized) - The Electron carriers (NADH and FADH2) go to the electron transport chain Electron Transport Chain, Chemiosmosis and Oxidative Phosphorylation - Occurs across the inner mitochondrial membrane - 4 protein complexes, the last complex holds oxygen - NADH drops its electrons off at complex 1 and FADH2 drops its electrons off at complex 2 ● When NADH drops off its electrons, NAD+ is available to be used again and H+ are also given off - Electrons are pulled down the chain by oxygen - Electrons cannot move between complexes on their own (charged ions), ubiquinone (Q) and cytochrome C (cyt c) act to shuttle electrons between protein complexes - When the electrons get to 4, they combine with O2 and H+ to form water Potential Energy of Electrons decrease as they move to the final electron acceptor: Oxygen - As electrons move down the electron transport chain, they give off a bit of energy - This release of energy is used to active some of the protein complexes of the electron transport chain that act as proton pumps (involved in active transport of H+)

Gradient Creates Proton Motive Force - H+ build up within the inner mitochondrial membranes forming an electrochemic gradient called the Proton Motive Force - Mitrochondrial membrane is impermable to H+ (due to charge) - Energetically favorable to diffuse across the membrane ● ATP Synthase is needed Chemiosmosis: movement of H+ across ATP synthase from high to low concentration - ATP Synthase is a motor that cayalyzes phosphorylation of ADP ● Flow of protons through ATP synthase causes the rotor and shaft region of this enzyme to spin, causing a conformational change that cyalyzes the addition of phosphate groups to ADP forming ATP - Oxidative Phosphorlyation: the addition of phosphate groups to ADP to form ATP via ATP synthase occurs within Chemiosomosis ● Results in the formation of 25 ATP per glucose - Analogous to a dam with large turbines ● As protons (H+) move through ATP synthase, it causes the rotor portion of this enzyme to spin, this kinetic energy is converted into chemical energy which results into ATP

Cellular Respiration with no oxygen present: fermentation - Electrons are not pulled down ETC, proton pumps stop, no proton motive force, drastic reduction in ATP Some Eukaryotic cells ( years, muscle cells) can undergo fermentation - Glycolysis still occurs but instead of oxygen accepting the electrons, the electrons from NADH are given back to pyruvate (lactic acid fermentation) or to an intermediate (alcohol fermentation) to regenerate NAD+...