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CONCEPT: OVERVIEW OF AEROBIC RESPIRATION Cellular respiration is a series of reactions involving electron transfers to breakdown molecules for (ATP) 1. Glycolytic pathway: Glycolysis and Fermentation 2. Pyruvate (end product of glycolysis) is oxidized (loss of electrons) to create acetyl CoA 3. Tricarboxylic cycle (Krebs cycle or citric acid cycle) oxidizes acetyl CoA to create CO2 4. Electrons are transferred through the electron transport chain 5. ATP synthesis occurs EXAMPLE: Steps of cellular respiration Page 2
Oxidative phosphorylation is the series of reactions that oxidizes molecules and uses electrical energy to generate ATP Involves chemiosmotic coupling of a proton electrochemical gradient and ATP synthesis - Stage 1: Electron transport chain (#4) pumps H + across a membrane creating electrochemical gradient - Stage 2: ATP synthesis (#5 above) allows H + to flow down their gradient through proteins that create ATP - Proton motive force is the H + electrochemical gradient used to drive ATP synthesis EXAMPLE: Process of oxidative phosphorylation Page 3
PRACTICE 1. Which of the following shows the correct steps of cellular respiration? a. Glycolysis Pyruvate Reduction TCA ATP Production ETC b. Pyruvate Reduction Glycolysis TCA ATP Production ETC c. Glycolysis TCA Pyruvate Reduction ATP Production ETC d. Glycolysis Pyruvate Reduction TCA ETC ATP Production 2. Oxidative phosphorylation includes all but which of the following? a. Chemiosmotic coupling of a proton electrochemical gradient and ATP synthesis b. Electron transport chain c. ATP synthesis d. Glycolysis Page 4
CONCEPT: MITOCHONDRIA The mitochondria has a distinctive structure It is surrounded by membranes - Outer membrane: Contains porin proteins which allow larger molecules to flow into - Intermembrane space: Space between the two membranes. Chemically equivalent to cytosol - Inner membrane: Impermeable to ions and small molecules contains transmembrane proteins - Site of oxidative phosphorylation - Folded into cristae, which are infolds that increase the surface area of the membrane The matrix is the internal space of the mitochondria EXAMPLE: Mitochondria structure The mitochondria have characteristics Mitochondria can remain in fixed locations, or can move throughout the cell by traveling on microtubules Mitochondria can fuse together to create long tubular networks Mitochondria have their own, circular DNA genome - Encodes for 13 polypeptides, 22 trnas, and 2rRNAs - Create their own ribosomes that exist within the mitochondrial matrix Page 5
Mitochondria must important cellular proteins into the matrix EXAMPLE: Fused mitochondria form tubular networks PRACTICE 1. Match the mitochondrial structure with the correct definition I. Outer membrane II. Intermembrane space III. Inner membrane IV. Cristae V. Matrix a. Space between the two membranes b. Internal space of the mitochondria c. Contains porin proteins which allow larger molecules to flow into d. Impermeable to ions and small molecules e. Infolds that increase the surface area of the membrane Page 6
2. Which mitochondrial structure is the location of oxidative phosphorylation? a. Outermembrane b. Intermembrane space c. Inner membrane d. Matrix 3. True or False: Mitochondria always exist as distinct organelles that never come together to form larger structures. a. True b. False Page 7
CONCEPT: CITRIC ACID CYCLE (KREBS CYCLE - TCA CYCLE) Overview The citric acid cycle is a set of metabolic reactions that occur after glycolysis to CO2 and NADH Pyruvate (glycolysis product) is decarboxylated (removes carboxyl group and releases CO2) to create acetyl CoA - Acetyl CoA is the starting molecule for the citric acid cycle - The pyruvate dehydrogenase complex is the group of proteins responsible for this reaction The citric acid cycle oxidizes acetyl CoA to 1 GTP, 3 NADH, and 1 FAHD2 - The NADH is passed to the next step in cellular respiration (electron transport chain) The requirement for oxygen is indirect (the citric acid cycle doesn t use oxygen) but it is still classified as aerobic - The electron transport chain needs oxygen to replace the NAD + used by the citric acid cycle EXAMPLE: Overview of the Citric Acid Cycle Page 8
Cycle Steps 1. Citrate Synthesis - Water is consumed and CoA is released Acetyl-CoA Oxaloacetate Citrate 2. Isomerization (rearrangement of atoms) - Hydroxyl group is isomerized Citrate Cis-aconitate isocitrate 3. CO2 and NADH creation - Carbon oxidation creates CO2 and NADH isocitrate a-ketoglutarate Page 9
4. CO2 and NADH creation (Second time) - Second oxidation creates more CO2 and NADH a-ketoglutarate Succinyl-CoA 5. GTP creation Succinyl-CoA Succinate 6. FADH2 creation - Third oxidation results in creation of FADH2 Succinate Fumarate Page 10
7. Addition of Water - Water is added which adds a hydroxyl group next to the carbonyl atom Fumarate L-malate 8. NADH creation - Four oxidation leads to NADH creation and oxaloacetate (used in step 1) L-malate Oxaloacetate Page 11
EXAMPLE: Review of the Citric Acid Cycle Page 12
PRACTICE 1. Which of the following is not a product of the citric acid cycle? a. NADH b. CO2 c. FADH2 d. Acetyle CoA 2. For each acetyl CoA that is oxidized in the citric acid cycle, what is created? a. 1 GTP, 3 NADH, and 1 FAHD2 b. 2 GTP, 1 NADH, and 3 FAHD2 c. 6 GTP, 2 NADH, and 1 FAHD2 d. 1 GTP, 1 NADH, and 1 FAHD2 Page 13
3. The citric acid cycle requires oxygen indirectly, because oxygen is necessary for what to occur? a. Replace FADH b. Replace GDP c. Replace ADP d. Replace NAD + 4. What is the starting molecule for the citric acid cycle? a. Glucose b. Pyruvate c. Acetyl CoA d. Citrate Page 14
CONCEPT: ELECTRON TRANSPORT CHAIN Overview The electron transport chain uses energy from activated carriers to drive the creation of an H + gradient for ATP synthesis The first stage of oxidative phosphorylation is the electron transport chain The electron transport chain is embedded in the mitochondrial membrane NADH and FADH2 are the two activated carriers that donate electrons to the electron transport chain - They are oxidized to NAD + and FAD Stepwise movement of high energy electrons through protein complexes allows for energy capture and transfer - The last electron acceptor is O2 which forms EXAMPLE: Overview of the electron transport chain Steps from NADH and FADH2 are fed through the four complexes of the electron transport chain NADH dehydrogenase transfers electrons to ubiquinone (coenzyme Q), a hydrophobic e - carrier in lipid bilayer) - Contains iron-sulfur centers which are iron-sulfur linkages which can accept or donate electrons - Moves four H + into the intermembrane space Succinate dehydrogenase transfers low-energy electrons from succinate to FAD then to ubiquinone - Contains iron-sulfur centers - Does not move H + across membranes Page 15
EXAMPLE: First two steps to the electron transport chain Cytochrome bc1 catalyzes the transfer of electrons from ubiquinol (reduced form of ubiquinone) to cytochrome C (electron carrier in the intermembrane space) - Contains heme groups which bind iron and undergo iron oxidation to allow for accepting/donating e - - Moves four H + into the intermembrane space (sometimes called the Q cycle) - Can also be called the CoQH2 cytochrome c reductase Cytochrome C oxidase transfers electrons to O2 (Consumes the majority of the air we breathe) - Contains a copper center (core of cooper atoms that accept/donate electrons) and a heme group - After accepting two electrons, it binds O2 tightly, breaks the double bond, and each O accepts a pair of e - - For each Oxygen there are 2 H + moved into the intermembrane space and 2 H + used to create H2O EXAMPLE: Last two steps to the electron transport chain Page 16
EXAMPLE: The entire electron transport chain Reduction Potentials Each complex in the electron transport chain has a redox potential (E o ) which measures the affinity of electrons in Volts High electrons-transfer potential: Strong reducing agents (V<0, ex: NADH) Low electron-transfer potential: Strong oxidizing agents (V>0 ex: Oxygen) The electron transport chain is arranged in order of reduction potentials - NADH à NAD + + H + = -320mV - 2 H + + ½ O2 + 2e - à H2O = 816mV EXAMPLE: Increase of redox potentials down the ETC redox potential mv -400-200 0 200 400 600 800 NADH NAD + H+ NADH dehydrogenase complex Q ubiquinone H + Cytochrom bc 1 (reductase) complex cytochrome c c cytochrome c oxidase complex H + 1/2 O 2 + 2H + H 2 O Page 17 direction of electron flow
PRACTICE 1. Which of the following is not a complex of the electron transport chain? a. NADH dehydrogenase b. Succinate dehydrogenase c. Cytochrome C oxidase d. ATP dephosphorylase 2. Which of the following is the correct order of electrons through the electron chain? a. NADH dehydrogenase à succinate dehydrogenase à Cytochrome oxidase à Cytochrome bc1 b. succinate dehydrogenase à NADH dehydrogenase à Cytochrome oxidase à Cytochrome bc1 c. NADH dehydrogenase à succinate dehydrogenase à Cytochrome bc1à Cytochrome oxidase d. Cytochrome bc1à succinate dehydrogenase à Cytochrome oxidase à NADH dehydrogenase Page 18
3. Which of the following molecules is the last to accept electrons from the electron transport chain? a. CO2 b. Oxygen c. NAD + d. FAD 4. True or False: The reduction potentials of the complexes in the electron transport chain are ordered from low to high. a. True b. False Page 19
CONCEPT: ATP SYNTHESIS DRIVE FROM PROTON GRADIENTS An electrochemical proton gradient drives ATP The electrochemical proton gradient is created by an H + gradient and a voltage (charge) gradient - Occurs across the inner mitochondrial membrane - Driven by the electron transport chain Chemiosmotic coupling: Electron transport chain and H + pumping across a membrane drives ATP synthesis EXAMPLE: Chemiosmotic coupling across the inner mitochondrial membrane ATP synthase is the transmembrane that drives ATP synthesis In cell respiration the F1F0 ATP synthase drives ATP - Uses energy from the electrochemical proton gradient to create ATP - F0: The stationary head is responsible for catalyzing ATP synthesis (cytosolic side) - F1: Rotation of the g subunit drives proton translocation across the membrane ATP synthase can also run in - Uses energy from ATP to pump protons uphill Page 20
CELL BIOLOGY - CLUTCH EXAMPLE: ATP synthase H+ Fo H+ γ subunit F1 ADP ATP Proton pumping and ATP synthesis are events Proton pumping occurs in 4 main steps 1. An H+ moves into an empty binding site within the F0 subunit causing a conformational change 2. This conformational change displaces protons further up the channel 3. Protons change place, which causes rotation of the F1 channel 4. The rotation allows for the continual displacement and movement of protons down their gradient ATP synthesis occurs in three main stages which use energy from H+ translocation to increase affinity for ADP 1. O stage (open): The Fo head binds ATP poorly and ADP weakly 2. L stage (loose): The Fo head cannot bind ATP but binds ADP and Pi Page 21
3. T stage (tight): The Fo head binds ADP and Pi so tightly they spontaneously form ATP - The energy from two H + translocations triggers conformational changes and ATP synthesis - 100 molecules of ATP are made per second (3 ATPs per revolution) EXAMPLE: The O, L and T stages of ATP synthesis ADP + P i Loose Open Tight ATP Page 22
PRACTICE 1. Which of the following is not a stage of ATP synthesis? a. A stage b. O stage c. T stage d. L stage 2. Which one of the following structures is responsible for catalyzing the ADP to ATP reaction? a. F1 rotation b. F0 head c. g subunit Page 23
3. True or False: When ATPase is run backwards its purpose is to convert ATP to ADP to create a H + gradient. a. True b. False 4. Where does the ATPase get its energy to generate more ATP? a. Other ATP molecules b. GTP c. Hydrolysis of H2O d. Electrochemical proton gradient Page 24