Lecture 8 & 9 Ch9 Slides PDF

Cellular Respiration and Fermentation Cellular Respiration and Fermentation  I. Introduction - Redox Reactions Reduction-oxidation reactions (redox reactions) - chemical reactions that involve electron transfer Reduction – atom/molecule gains electron(s) Oxidation – atom...

Cellular Respiration and Fermentation Cellular Respiration and Fermentation  I. Introduction - Redox Reactions Reduction-oxidation reactions (redox reactions) - chemical reactions that involve electron transfer Reduction – atom/molecule gains electron(s) Oxidation – atom/molecule loses electron(s) These two processes are always coupled Electron donors are always paired with electron acceptors During redox reactions, electrons may: 1) be completely transferred from one atom to another 2) shift position in covalent bonds  I. Introduction - Redox Reactions cation (oxidized) NaCl anion (reduced)  I. Introduction - Redox Reactions Electron transfer during a redox reaction - often accompanied by a proton (H+) hydrogen (H) proton (H+) (one proton, one electron)  I. Introduction - Redox Reactions Electron transfer during a redox reaction - often accompanied by a proton (H+) Reduced molecules – gain protons - have a higher potential energy (more C-H bonds) Oxidized molecules – lose protons - have a lower potential energy (less C-H bonds) - can follow protons (H+) to determine if oxidation or reduction has occurred  II. Introduction - Adenosine Triphosphate (ATP) Adenosine triphosphate (ATP) - cellular currency for energy - provides the fuel for most cellular activities - works by transferring a phosphate group to another molecule - has high potential energy - four negative charges are confined to a small area - negative charges repel each other  II. Introduction - Adenosine Triphosphate (ATP) Adenosine triphosphate (ATP) - outermost phosphate group is cleaved - produces ADP and inorganic phosphate (Pi) - highly exergonic reaction (releases energy) - released phosphate can be transferred to target protein - can cause conformational change in its structure  III. Introduction - Enzymes Enzymes - protein catalysts - typically catalyze one specific reaction - biological chemical reactions occur at meaningful rates only in the presence of enzymes - enzymes bring substrates together in a precise orientation that makes reactions more likely Active site – region of enzyme to which the substrate binds (through hydrogen bonding and/or other weak interactions)  Questions When a molecule is reduced it generally: A) gains entropy B) loses entropy C) gains potential energy D) loses potential energy  Questions During photosynthesis, the transfer of electrons from water to the electron transport chain of chloroplasts yields oxygen. Apparently, some molecule of the transport chain must receive those electrons in a(n) _________ reaction. A) oxidation B) reduction C) hydrolysis D) condensation  Energy in the Form of Glucose Glucose – most organism’s preferred energy source - used to make ATP (high potential energy) Glucose is used to make ATP by two processes: a) Cellular Respiration b) Fermentation  Cellular Respiration Cellular Respiration Carbon atoms of glucose are oxidized to form carbon dioxide Oxygen atoms are reduced to form water Glucose is oxidized through a long series of carefully controlled redox reactions  Cellular Respiration Cellular Respiration Four steps: 1) Glycolysis - glucose is broken down (oxidized) to pyruvate 2) Pyruvate processing - pyruvate is oxidized to form acetyl CoA 3) Citric acid cycle - acetyl CoA is oxidized to CO 2 4) Electron transport and oxidative phosphorylation -compounds reduced in first three steps are oxidized in reactions that lead to ATP production  Cellular Respiration Cellular Respiration Four steps:  Cellular Respiration Cellular Respiration 1 Glucose 2 ATP + 2 ATP + 25 ATP 29 ATP  I. Glycolysis Glycolysis - a series of 10 chemical reactions that occur in cytoplasm - glucose is broken down into two molecules of pyruvate - releases potential energy that is used to convert ADP to ATP - does not require oxygen Two main phases: 1) Energy Investment Phase - 2 ATP molecules are used to phosphorylate glucose twice 2) Energy Payoff Phase - 2 pyruvate molecules produced - 2 molecules of NAD+ are reduced to NADH - 4 molecules of ATP are formed (net gain of 2 ATP)  I. Glycolysis Glycolysis 1) Energy Investment Phase - 2 ATP molecules are used to phosphorylate glucose twice - gives two molecules of glyceraldehyde-3-phosphate (G3P) G3P  I. Glycolysis Glycolysis 2) Energy Payoff Phase - 2 pyruvate molecules produced - 2 molecules of NAD+ are reduced to NADH - 4 molecules of ATP are formed (net gain of 2 ATP) 2 G3P produced by substrate-level phosphorylation  I. Glycolysis Substrate-level phosphorylation - ATP is produced by enzyme-catalyzed transfer of a phosphate group from a substrate to ADP - how ATP is produced in glycolysis and the citric acid cycle  I. Glycolysis Substrate-level phosphorylation - ATP is produced by enzyme-catalyzed transfer of a phosphate group from a substrate to ADP - how ATP is produced in glycolysis and the citric acid cycle Oxidative phosphorylation - an electron transport chain establishes a proton gradient - this gradient provides the energy for ATP production - how ATP is produced in the last step of cellular respiration  I. Glycolysis G3P 2 G3P produced by substrate-level phosphorylation  I. Glycolysis Summary of Glycolysis 1) one 6-carbon glucose converted to two 3-carbon pyruvate 2) reactions occur in the cytoplasm 3) energy that is released nets 2 ATP and 2 NADH  Cellular Respiration The remaining reactions occur in the mitochondria 1 Glucose 2 ATP + 2 ATP + 25 ATP 29 ATP  Cellular Respiration The remaining reactions occur in the mitochondria cristae – interior sac-like structures that are connected to inner membrane by short tubes inner membrane mitochondrial matrix intermembrane space outer membrane Pyruvate produced during glycolysis is transported into mitochondria  II. Pyruvate Processing Pyruvate Processing: - occurs in the mitochondrial matrix - catalyzed by the enzyme pyruvate dehydrogenase - pyruvate is converted into acetyl coenzyme A (or acetyl CoA) - one of the carbon atoms of pyruvate is oxidized to CO2 - 1 NADH is synthesized - no ATP is generated in this reaction  III. The Citric Acid Cycle Third step - known as: i) Citric Acid Cycle ii) Tricarboxylic acid (TCA) Cycle iii) Krebs Cycle  III. The Citric Acid Cycle Citric Acid Cycle - series of reactions involving eight carboxylic acids (COOH) - generally involves molecules in pathway becoming more oxidized - produces NADH, FADH 2, ATP/GTP and CO2  III. The Citric Acid Cycle citrate acetyl CoA (most reduced) = most potential energy oxaloacetate (most oxidized) = least potential energy - acetyl CoA links oxaloacetate (oxidized) to citrate (reduced) and the cycle starts again  III. The Citric Acid Cycle citrate 2 acetyl CoA (most reduced) 2 pyruvate oxaloacetate (most oxidized) glucose 1 glucose molecule drives 2 turns of the cycle  III. The Citric Acid Cycle Citric Acid Cycle - completes the oxidation of glucose  Oxidation of Glucose First three steps of Cellular Respiration - completely oxidizes glucose  Oxidation of Glucose First three steps of Cellular Respiration - completely oxidizes glucose Each glucose molecule: i) is oxidized to 6 CO2 (exhaled as waste) ii) reduces 10 molecules of NAD+ to NADH iii) reduces 2 molecules of FAD to FADH2 iv) produces 4 ATP (by substrate level phosphorylation) Most of glucose’s original energy is still contained in NADH and FADH2 - this reducing power is used to produce large amounts of ATP through oxidative phosphorylation  Questions If radioactive sugar was fed to a mouse, the radioactivity would progress along which of the following routes? A) sugar to Citric Acid Cycle to pyruvate to CO2 B) sugar to Citric Acid Cycle to pyruvate to O2 C) sugar to pyruvate to Citric Acid Cycle to O2 D) sugar to pyruvate to Citric Acid Cycle to CO2  Questions If lactic acid fermentation is an example of substrate-level phosphorylation, then: A) the process involves enzymes that transfer a phosphate group from a substrate molecule to ADP B) the energy of a proton gradient is used to produce ATP C) the process must occur in the mitochondria D) the process must occur in the cytoplasm  IV. The Electron Transport Chain Electron Transport Chain (ETC) - involves molecules that oxidize NADH and FADH2 - energy released by these redox reactions is used to move protons (H+) across inner membrane of mitochondria to form a proton gradient  IV. The Electron Transport Chain Electron Transport Chain (ETC) - involves molecules that oxidize NADH and FADH2 - energy released by these redox reactions is used to move protons (H+) across inner membrane of mitochondria to form a proton gradient  IV. The Electron Transport Chain Electron Transport Chain (ETC) - involves molecules that oxidize NADH and FADH2 - energy released by these redox reactions is used to move protons (H+) across inner membrane of mitochondria to form a proton gradient - proton gradient is then used to make ATP through oxidative phosphorylation  IV. The Electron Transport Chain Electron Transport Chain (ETC) - involves molecules that oxidize NADH and FADH2 - energy released by these redox reactions is used to move protons (H+) across inner membrane of mitochondria to form a proton gradient - proton gradient is then used to make ATP through oxidative phosphorylation inner membrane  IV. The Electron Transport Chain Electron Transport Chain (ETC) - comprised of 4 multi-protein complexes (Complex I-IV) - reside in inner membrane of mitochondria I II III IV  IV. The Electron Transport Chain Electron Transport Chain (ETC) - comprised of 4 multi-protein complexes (Complex I-IV) - reside in inner membrane of mitochondria  IV. The Electron Transport Chain Electron Transport Chain (ETC) - comprised of 4 multi-protein complexes (Complex I-IV) - reside in inner membrane of mitochondria - electrons are transferred between complexes by: 1) Coenzyme Q - between Complex I/II and III 2) Cytochrome c (Cyt c) - between Complex III and IV  IV. The Electron Transport Chain Electron Transport Chain (ETC) - comprised of 4 multi-protein complexes (Complex I-IV) - reside in inner membrane of mitochondria - electrons are transferred between complexes by: 1) Coenzyme Q - between Complex I/II and III 2) Cytochrome c (Cyt c) - between Complex III and IV - electronegativities of molecules holding electrons increases with each step - electrons are held more and more tightly - therefore energy is released as electrons are transferred  IV. The Electron Transport Chain Electron Transport Chain (ETC) - comprised of 4 multi-protein complexes (Complex I-IV) - reside in inner membrane of mitochondria - electrons are transferred between complexes by: 1) Coenzyme Q - between Complex I/II and III H2 O2 2) Cytochrome c (Cyt c) - between Complex III and IV energy potential drops energy H2O - electronegativities of molecules holding electrons increases with each step - electrons are held more and more tightly - therefore energy is released as electrons are transferred  IV. The Electron Transport Chain Electron Transport Chain (ETC) - energy released as electrons pass through ETC - used to pump protons across the inner membrane  IV. The Electron Transport Chain Electron Transport Chain (ETC) - electrochemical gradient forms across inner membrane NADH donates electrons to Complex I Complex I pumps protons (H+) into intermembrane space FADH2 donates electrons to Complex II  IV. The Electron Transport Chain Electron Transport Chain (ETC) - electrochemical gradient forms across inner membrane Complex I and Complex II both pass electrons to Coenzyme Q Coenzyme Q moves protons (H+) into intermembrane space - donates electrons to Complex III  IV. The Electron Transport Chain Electron Transport Chain (ETC) - electrochemical gradient forms across inner membrane Complex III transfers electrons to Cytochrome c Cytochrome c passes electrons to Complex IV Complex IV pumps protons (H+) into intermembrane space  IV. The Electron Transport Chain Electron Transport Chain (ETC) - electrochemical gradient forms across inner membrane O2 is the final electron acceptor in the ETC - accepts electrons and protons to form H2O Our Cellular Respiration is an Aerobic process  IV. The Electron Transport Chain Electron Transport Chain (ETC) - electrochemical gradient forms across inner membrane O2 is the final electron acceptor in the ETC - accepts electrons and protons to form H2O Our Cellular Respiration is an Aerobic process  IV. The Electron Transport Chain Electron Transport Chain (ETC) - creates a proton gradient across inner membrane How is this gradient used to produce ATP?  Using the Proton Gradient to Make ATP Scientists assumed ATP was being produced by substrate- level phosphorylation - but no suitable enzyme was found among the ETC components  Using the Proton Gradient to Make ATP ATP synthase: i) Base – transports protons across membrane ii) Knob – catalyzes the phosphorylation of ADP to ATP iii) rotor shaft – spins Knob iv) stator – stabilizes units Flow of protons through Base Base causes rotor shaft to spin Knob changes conformation and catalyzes the conversion of ADP into ATP Knob - establishes a clear link between proton transport and ATP synthesis  Using the Proton Gradient to Make ATP Chemiosmosis Hypothesis – a proton gradient is used to drive energy-requiring processes (ATP production) In this way, ATP is generated by a proton-motive force Base Knob  Using the Proton Gradient to Make ATP Electron Transport Chain (ETC) - establishes a proton electrochemical gradient across inner membrane Base Knob ATP synthase - uses potential of gradient to produce ATP Oxidative phosphorylation - links oxidation of NADH and FADH2 to the phosphorylation of ADP to ATP  Using the Proton Gradient to Make ATP Electron Transport Chain (ETC) - establishes a proton electrochemical gradient across inner membrane Substrate-level phosphorylation Oxidative phosphorylation Base Knob ATP synthase - uses potential of gradient to produce ATP  Summary of Cellular Respiration cristae – interior sac-like structures that inner membrane are connected to inner membrane intermembrane space outer membrane mitochondrial matrix  Questions Creating pores in the membranes of mitochondria immediately reduces ATP synthesis. A likely explanation for this observation is _________: A) leakage of carbon dioxide B) leakage of glucose C) leakage of hydrogen ions D) leakage of oxygen  Questions In eukaryotes, components of the Electron Transport Chain reside in: A) the cytoplasm B) the outer membrane of the mitochondria C) the intermembrane space of mitochondria D) the inner membrane of the mitochondria  Summary of Cellular Respiration O2 final electron acceptor of aerobic cellular respiration What happens in the absence of oxygen?  Aerobic and Anaerobic Respiration For an organism that relies on aerobic respiration - reduced levels of oxygen create a serious problem - the ETC cannot function - NADH is not converted into a proton gradient - NADH levels increase, NAD + abundance decreases Glycolysis requires NAD+ to proceed 2 G3P  Aerobic and Anaerobic Respiration For an organism that relies on aerobic respiration - reduced levels of oxygen create a serious problem - the ETC cannot function - NADH is not converted into a proton gradient - NADH levels increase, NAD + abundance decreases Glycolysis requires NAD+ to proceed - without Glycolysis, no ATP can be produced - NADH pools must be oxidized to NAD + to allow glycolysis to continue - this occurs through the process of Fermentation  Fermentation Fermentation - metabolic pathway that regenerates NAD + by oxidizing stockpiles of NADH - allows glycolysis to continue producing some ATP (through substrate-level phosphorylation) - pyruvate becomes an electron acceptor - pyruvate is reduced to a waste product, while NADH is oxidized to NAD+ 2 ATP through substrate-level phosphorylation  Fermentation Fermentation 1) Humans  Fermentation Fermentation 1) Humans Lactic acid is a waste product Increased rate of breathing brings in more O2 to revive ETC  Fermentation Fermentation 2) Yeast  Fermentation Fermentation 2) Yeast (alcohol & CO2) Alcohol is a waste product of yeast  Fermentation Fermentation - very inefficient (2 ATP per glucose molecule) compared to Cellular Respiration (29 ATP per glucose molecule)  Fermentation Fermentation - very inefficient (2 ATP per glucose molecule) compared to Cellular Respiration (29 ATP per glucose molecule) Facultative anaerobes - organisms that can switch between Fermentation and Cellular Respiration - will always prefer the latter if O 2 is available 2 ATP through substrate-level phosphorylation  Fermentation Fermentation - very inefficient (2 ATP per glucose molecule) compared to Cellular Respiration (29 ATP per glucose molecule) Facultative anaerobes - organisms that can switch between Fermentation and Cellular Respiration - will always prefer the latter if O 2 is available Some of our cells function as facultative anaerobes to some extent - very limited - we cannot survive as facultative anaerobes Lactic acid production  Question A scientist tries to use yeast to ferment sugar into alcohol. While they discover that the sugar has been metabolized, they find that no alcohol is detectable. A plausible explanation for this observation is: A) they waited too long and the yeast metabolized the alcohol B) they did not grow the culture in aerobic conditions C) they did not grow the culture in anaerobic conditions D) yeast fermentation produces lactic acid instead of alcohol  Summary 1) Cells use Cellular Respiration to produce ATP when O2 is present Four Stages: i) Glycolysis ii) Pyruvate oxidation iii) Citric acid cycle iv) Electron Transport Chain  Summary 1) Cells use Cellular Respiration to produce ATP when O2 is present Four Stages: i) Glycolysis ii) Pyruvate oxidation iii) Citric acid cycle iv) Electron Transport Chain 2) ATP is made by: a) Substrate-level phosphorylation (in Glycolysis and Citric Acid Cycle) b) Oxidative phosphorylation (in the ETC)  Summary 1) Cells use Cellular Respiration to produce ATP when O2 is present Four Stages: i) Glycolysis ii) Pyruvate oxidation iii) Citric acid cycle iv) Electron Transport Chain 2) ATP is made by: a) Substrate-level phosphorylation (in Glycolysis and Citric Acid Cycle) b) Oxidative phosphorylation (in the ETC) 3) Cells use Fermentation to produce ATP in the absence of O2 - very inefficient use of sugar