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Cell Respiration Biology AP Todeschini Photosynthesis and Respiration • There is a reciprocal relationship between chemoheterotrophs and photoautotrophs All Animals Must Eat to Obtain Energy Controlled Energy Conversion • Metabolic reactions are tightly controlled in multi-step metabolic pathways. • FYI, if this didn’t happen your body would burst into flames… Catabolic Reactions • “Destroy” = Break down food (few organic molecules) into (many) simpler molecules • This is an exergonic reaction • This reaction releases energy • Two famous catabolic processes for food • Fermentation • Cellular Respiration (more efficient) • How is food broken down? How does breakdown release energy? Redox Reactions • Chemical reactions where electrons are transferred from one atom to another • OIL RIG = Oxidation Is Loss; Reduction Is Gain Visualizing Terminology (practice) X reduces Y X becomes oxidized Xe- + Y X Ye- + Y becomes reduced Y oxidizes X Na becomes oxidized Na+ becomes reduced Cl becomes reduced Cl- becomes oxidized Na + Cl ↔ Na+ Na reduces Cl Cl oxidizes Na + ClNa+ oxidizes Cl- *Note Reaction is reversible… Cl- reduces Na+ Redox Energetics • One reactant gains energy – reduced • One reactant loses energy – oxidized • How do you know if overall reaction is exergonic or endergonic? • Cellular Respiration (Exergonic, Catabolic) • C6H12O6 + 6O2 6CO2 + 6H2O + Energy • Photosynthesis (Endergonic, Anabolic) Energy + 6CO2 + 6H2O C6H12O6 + 6O2 • Methane combustion (burning natural gas) • CH4 + 2O2 CO2 + 2H2O + Energy Redox w/ Cellular Respiration • Cellular Respiration breaks down glucose • Glucose is oxidized loses electrons • Release energy in a controlled manner • Oxidize glucose little by little How many electrons? • Strip electrons a few at a time • Use electron carriers (NADH) via ETC • Biochemical pathway with several enzymes If release energy all at once… http://www.youtube.com/watch?v=txkRCIPSsjM Electron Shuttles • Compounds the store electrons from food • Exist in oxidized and reduced forms • In cells electrons come with protons • Transfer electrons and protons to other areas of the cell to continue metabolism General Overview of Cell Respiration • Cellular respiration has three stages: 1. 2. 3. Glycolysis (breaks down glucose into two molecules of pyruvate) The citric acid cycle (completes the breakdown of glucose) Oxidative phosphorylation (accounts for most of the ATP synthesis) • Anaerobic Respiration stops with glycolysis • Aerobic respiration will occur in a mitochondria with oxygen present(in eukaryotes only). • The point of all of it is to make ATP Fig. 9-6-1 Electrons carried via NADH Glycolysis Pyruvate Glucose Cytosol ATP Substrate-level phosphorylation Fig. 9-6-2 Electrons carried via NADH and FADH2 Electrons carried via NADH Citric acid cycle Glycolysis Pyruvate Glucose Mitochondrion Cytosol ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Fig. 9-6-3 Electrons carried via NADH and FADH2 Electrons carried via NADH Citric acid cycle Glycolysis Pyruvate Glucose Oxidative phosphorylation: electron transport and chemiosmosis Mitochondrion Cytosol ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation Glycolysis (in cytoplasm) • All respiration begins with glycolysis in the cytoplasm • Glucose (6C) is cleaved into 2 molecules of pyruvate (3C) • This requires 2 ATP. It produces 4 • 2NAD+ are reduced to 2 NADPH Glycolysis • Substrate level phosphorylation • When ATP is produced by enzymatic phosphate transfer from another organic phosphate • Occurs in glycolysis and citric acid(Kreb’s) cycle • Glycolysis is hypothesized to be most ancient metabolic pathway because it happens in all organisms • What’s next??? Fermentation • NADH is oxidized back into NAD+ • Pyruvate must be reduced into another compound(waste product) • Ethanol(yeast) • Lactic acid(animals) • Glycolysis can continue indefinitely, but costly After Glycolysis • In presence of oxygen Aerobic Respiration Mitochondrialots of ATP(very efficient) • No oxygen Anaerobic Fermentationcytoplasmlactic acid(animals) or ethanol(microorganisms) • Anaerobic respiration produces 2 ATP per glucose making it much less efficient than aerobic which produces ~38 total per glucose. Citric Acid Cycle (Kreb’s Cycle) • Following glycolysis, aerobic respiration in eukaryotes will take place in the mitochondrion. • The products of glycolysis are transported through the mitochondrial membranes into the mitochondrial matrix. • This is where the citric acid cycle occurs. • Prokaryotes that carry out aerobic respiration utilize specializing portions of their cell membrane. First Acetyl-CoA (intermembrane space) • While being transported into the mitochondrion, pyruvate is converted into acetyl group (-CH2CH3) and a molecule of CO2 • The CO2 is waste product. • The acetyl group is attached to a molecule of CoEnzymeA (CoA). This is the carbon input into the citric acid acid cycle. • Another NAD+ is reduced to NADH Citric Acid Cycle(matrix) • The acetyl group from pyruvate is attached to oxaloacetate, forming citric acid(aka citrate) • The carbons from the acetyle group are oxidized into 2CO2 • 3 molecules of NAD+ are reduced into NADH • 1 molecule of FAD is reduced into FADH2 • 1 ATP is produced • The citrate is converted back into oxaloacetate. *this happens 2X per glucose Oxidative Phosphorylation (intermembrane space) • Electrons are from NADH and FADH2 are transported through a series of proteins found in the folds of the cristae (electron transport chain). • H+ are pumped into and build up in the intermembrane space and will eventually flow across ATP synthase to generate ATP. • Oxygen is the “final electron acceptor”. It will “grab” the electrons and H+ to forms water, a harmless waste product. Chemiosmosis • Ultimately how ATP is produced. • H+ protons can only diffuse back into the matrix through the ATP synthase channel. • The free energy that is released is used to catalyze ATP formation from ADP and free phosphate groups(“oxidative phosphorylation”) https://www.youtube.com/watch?v=JnQqbMg74Hk It’s not all about glucose… • All macromolecules can be used as substrates for respiration. • Different components enter at different points. • If an animal is starving it will digest molecules in the following order: • Carbsfatsproteins(as a last resort) • A fat gram will produce 2X as much ATP as a gram of carbohydrate • Gluconeogenesis is a way the body can create substrates for respiration, costly Overview of all Steps Glycolysis(cytoplasm) Transition Step(cytoplasm) Inputs Inputs • Glucose (6C) • 2 pyruvate (3C) • 2 NAD+ • 2 NAD+ • 2 ATP Outputs Outputs • 2 Acetyl-CoA (2C from pyruvate) • 2 Pyruvate (3C) • 2NADH • 4 ATP • 2CO2 • 2 NADH Citric Acid Cycle(mitochondria matrix) Inputs • 2 Acetyl-CoA (2C from pyruvate) • 6 NAD+ • 2 FAD • 2 ADP Outputs • 4 CO2 • 6 NADPH • 2 FADH2 • 2 ATP ETC(inner membrane) Inputs • 20 NADH • 2 FADH2 • O2 Outputs • ~32-34 ATP • H2O • 20 NAD+ • 2 FAD+