Chapter 9: Cellular Respiration AP Biology

Oxidation and Reduction E is gained by the transfer of e ’ s The relocation of e- ’ s releases the stored E and the E ultimately makes ATP

Redox Reactions Oxidation: the loss of e- ’ s from a substance Reduction: the gain of e- ’ s by a substance E must be added to pull e- ’ s from an atom

Redox Reactions A redox reaction that relocates an e- from a less electronegative atom to a more electronegative atom loses potential E

Hydrogen In most redox reactions, it is not only the e- that is transferred but in most biological reactions the whole hydrogen atom is transferred

Carbohydrates and Fats Contain high levels of hydrogen and their electrons There is a barrier that keeps sugar from combining immediately with O 2 This barrier is reduced inside the body with the help of enzymes

Cellular Respiration C 6 H 12 O 6 + 6O 2  6H 2 O + 6CO 2 + E

Introduction Cellular Respiration is a catabolic pathway. –Does not directly perform cellular work??? –Redox reactions!! –Importance of Hydrogen??

Introduction Does glucose react instantaneously? Spontaneously? Activation barrier/ Enzymes(lots of them) –Lowers activation energy –Allows breakdown to proceed spontaneously

Cellular Respiration What is a potential problem with the breakdown of glucose as a spontaneous reaction?? –Hint: TNT, Gasoline How does the cell prevent this problem? –Does not release energy all at once –Multi- step process catalyzed by specific enzymes

Cellular Respiration With each step, electrons are released with a proton (hydrogen atom) Each hydrogen is transferred to a coenzyme (NAD+) And eventually to Oxygen

Nicotinamide Adenine Dinucleotide NAD+ Derivative of the vitamin niacin Coenzyme –Oxidizing agent Will be reduced to NADH –(2 electrons and Hydrogen) –Dehydrogenase-removes two hydrogen from substrate

Nicotinamide Adenine Dinucleotide

Glycolysis: Occurs in the cytoplasm Net gain of 2 ATP and 2 NADH Start: 6 carbon glucose End: 2- 3 carbon pyruvate molecules Ten steps- two phases –Energy investment phase –Energy payoff phase

Glycolysis: Energy investment stage: Glucose phosphorylated by ATP(2) –Unstable –Splits Each 3 carbon molecule is phosphorylated again –Inorganic phosphate comes from cytosol not ATP

Glycolysis: Energy Payoff Phase: Each 3 carbon molecule reduces NAD+ to NADH Each 3 carbon molecule gives up its 2 phosphates to ADP to form 4 ATP.

Glycolysis: Summary Reactants: –Glucose –NAD+ –ATP (2) –ADP (2) Products: Pyruvate (2) NADH (2) ATP (4)

Mitochondria Structure Double membrane organelle –Outer membrane: very permeable –Inner membrane: selectively permeable –pyruvate (yes) –NADH (no) contains electron transport proteins Cristae- inner foldings –Increase surface area similar to plasma membrane of bacteria

Mitochondria Structure Double membrane organelle –Matrix: inside inner membrane Protein rich solution: enzymes In between cristae

–Krebs Cycle Tricarboxylic Acid Cycle –Matrix –Reactants: 2 molecules of pyruvate Each makes a circuit through the cycle –One glucose = two pyruvate = two turns of the cycle –Products: For each pyruvate –3 NAD+ 3 NADH –1 FAD+ 1 FADH 2 –1 ADP + P 1 ATP Citric Acid Cycle:

Oxidation of Pyruvate: Pyruvate must first be converted to Acetyl CoA –Pyruvate dehydrogenase –Each pyruvate molecule loses one Carbon and two Oxygen- Acetyl group –Acetyl group attaches to CoA molecule forming acetyl CoA –Reduction of NAD+ molecule to NADH 2 total- one for each pyruvate

Cyclic Nature of Citric Acid Cycle CoA transfers 2 carbon molecu le –Transfers 2 carbon acetyl group to 4 carbon oxaloacetate –Results = 6 carbon citrate –Start of cycle

Cyclic Nature of Citric Acid Cycle Citrate- goes through a series of oxidation reactions –Priming/ rearrangement stage Prepares the 6 carbon citrate for energy extraction –Oxidized by NAD+ –Carbon dioxide

Cyclic Nature of Citric Acid Cycle Citrate also loses 2 carb on atoms (CO2) eventually returning to 4 carbon oxaloacetate again –Energy Extraction/ Acetyl group stage –More reduction of NAD+ –Reduction of FAD –ATP produced- substrate level phosphorylation –Cycle starts over again

Important Features NAD+ and FAD+ are reduced by the oxidation of an organic compound (transfer of H atom). 1 ATP molecule is formed by substrate level phosphorylation during each turn of cycle (net per glucose = 2 ATP) For each turn of the cycle, 3 Carbon atoms are lost to Carbon Dioxide –All 6 carbons exit the system by the end of the Kreb cycle.

Oxidative Phosphorylation Electron transport is coupled with ATP synthesis via chemiosmosis. Over all drop in ΔG as electrons are transferred from NADH to Oxygen –Releases energy in manageable amounts Create proton motive force –Drives the production of ATP

Electron Transport Chain Inner Mitochondrial membrane Series (I - IV) of protein complexes –Complexes one – three have increasing affinity for electrons Prosthetic groups: non-protein components essential to certain enzymes Redox (downhill) reactions Does not directly make ATP- eases the fall

Prosthetic Groups: FMN- flavin mono nucleotide- –Gets reduced by NADH at complex I CoQ- Ubiquinone- –very hydrophobic – very mobile –Carries between complex I/II and complex III

Prosthetic Groups: Iron/Sulfur cluster- –gets reduced by FADH2 at complex II –Transfer electrons between cytochromes Cytochromes- transfers electrons to oxygen –Heme- Fe atom- carries electrons

Chemiosmosis The formation of a hydrogen ion gradient drives the cellular process of ATP synthesis –Proton motive force

Chemiosmosis Final protein complex = F 0 F 1 protein –Catalyzed by ATP synthase –Oxidative phosphorylation: synthesis of ATP from ADP and P i –3 to 4 H+ to generate 1 ATP

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Fermentation  If a cell runs out of O 2, all the e- carriers are stuck in reduced form, halting system Pyruvate produced by glycolysis acts as alternative acceptor of H from NADH, keeping glycolysis going to allow small ATP production

Alcoholic Fermentation Yeasts break down sugar into pyruvate. Each pyruvate is dismantled into a molecule of CO2 and a 2C compound acetaldehyde Acetaldehyde is reduced by accepting 2H's from NADH and H+ forming 2C alcohol ethanol (ethyl alcohol)

Lactic Acid Fermentation Occurs during strenuous exercise Pyruvate from glycolysis is reduced by accepting hydrogens from NADH and H+ Pyruvate converted into 3C compound, lactate

Metabolic Energy Systesm: Phosphagen pathway- high powered activities that last around 10 secs Glycolytic pathway- moderately powered activities that last two minutes Oxidative pathway- low powered pathways that last more than several minutes

Respiration W/O O 2  Anaerobic respiration: uses nitrate or sulfate as final electron acceptor  Fermentation: the anaerobic breakdown of food molecules in which the final e- acceptor is an organic molecule