Cellular Respiration 1306 Biology For Majors 1 PDF

Learning Goals Cellular Respiration: How cells harvest energy from Carbohydrates 1306: Biology for Majors 1 Jenifer Gifford, Ph.D. [email protected] 1 1. Describe the purpose of cellular respiration, the names and locations of the main steps, and the main products 2. Know the reactants that go in a...

Learning Goals Cellular Respiration: How cells harvest energy from Carbohydrates 1306: Biology for Majors 1 Jenifer Gifford, Ph.D. [email protected] 1 1. Describe the purpose of cellular respiration, the names and locations of the main steps, and the main products 2. Know the reactants that go in and the products that come out of each of the four steps of cellular respiration (Glycolysis, Pyruvate Oxidation, Citric Acid Cycle, and Oxidative Phosphorylation) • Name and number of each product 3. Understand the difference between substrate level phosphorylation and oxidative phosphorylation 4. Explain how the electron transport chain powers the final production of ATP by the ATP synthase 5. Describe how each step is regulated by intentional mechanisms or the presence of inhibitors or other malfunctions in cellular machinery. 6. Explain the differences between aerobic respiration, anaerobic respiration, and anaerobic fermentation 7. Compare and Contrast the Process of Photosynthesis and Cellular Respiration 2 Photosynthesis and cellular respiration provide energy for life Cells and The Body Require ATP to Function • Most ecosystems: energy ultimately comes from the sun. • Photosynthesis: energy in sunlight is captured by chloroplasts • atoms of carbon dioxide and water are rearranged • sugar and oxygen are produced 3 4 1 Photosynthesis and cellular respiration provide energy for life • Most ecosystems: energy ultimately comes from the sun. • Photosynthesis: energy in sunlight is captured by chloroplasts • atoms of carbon dioxide and water are rearranged • sugar and oxygen are produced • Cellular respiration: • sugar is broken down to carbon dioxide and water • the cell captures some of the released energy to make ATP • Happens in mitochondria Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts CO 2 + H 2O Cellular respiration in mitochondria ATP • Some energy is lost as heat. Organic molecules + O2 ATP powers most cellular work Heat energy 5 Breathing supplies O2 for use in cellular respiration and removes CO2 Respiration, as it relates to breathing, and cellular respiration are not the same. • Respiration, in the breathing sense, refers to an exchange of gases. Usually an organism brings in oxygen from the environment and releases waste CO2. • Cellular respiration is the aerobic (oxygen-requiring) harvesting of energy from food molecules by cells. 6 Cellular Respiration C6H12O6 6 O2 6 CO2 Glucose Oxygen Carbon dioxide 6 H2O Cellular Respiration is a Catabolic Process ATP Heat Metabolism: All reactions in the body that involve energy transformation Water • Respiration breaks down sugars to make ATP • The body then uses the ATP to anabolically form large biomolecules like Nucleic acids, Proteins, and Lipids 7 8 2 Cellular Respiration is a Multistep Catabolic Breakdown of Glucose by Enzymes Cellular Respiration is also a Redox Reaction Recall: Oxidation Reduction reactions (redox reactions) are chemical reactions that involve electron transfer • During cellular respiration, (NADH/FADH2) Step by step breaking down of sugar allows some of the energy to be stored in other molecules and releases less heat • Glucose ultimately loses its hydrogen atoms (carrying electrons) and becomes oxidized to CO2. • Oxygen gains hydrogen atoms (carrying electrons) and becomes reduced to H2O. § “OIL RIG”: Oxidation Is Loss; Reduction Is Gain § “LEO the lion says GER”: Loss of Electrons is Oxidation; Gain of electrons is Reduction Loss of hydrogen atoms (becomes oxidized) Breakdown of Sugar in One Step releases a huge amount of heat C6H12O6 + 6 O2 6 CO2 + 6 H2O + ATP + Heat (Glucose) Gain of hydrogen atoms (becomes reduced) 9 10 Recall the role of Electron Carriers (NADPH/ NADH/ FADH2) • As glucose is being broken down, it’s electrons (and a H+) will be attached to electron carriers • Think of these electron carriers as unloaded (oxidized form) or loaded (reduced form) semi trucks NADP+, NAD+ and FAD NADPH, NADH and FADH2 Attaching Hydrogens to Electron Carriers is Part of the Redox Reactions that are taking place § Oxidation and reduction events are always coupled – If one atom loses an electron, another has to gain it – Electron donors are always paired with electron acceptors § When an atom or molecule gains an electron it is reduced (more neg. in charge) – Reduction = gain of one or more e- and a hydrogen ion (H+) § When an atom or molecule loses an electron it is oxidized (more pos. in charge) Sugar Becomes oxidized +2H – Oxidation = the loss of one or more e- 11 12 3 Cellular respiration begins with consuming and breaking down carbohydrates 13 Cytoplasm Mito. Cellular Respiration 4 Steps of AEROBIC Cellular Respiration 14 Aerobic Cellular respiration occurs in 3 main stages You’d be wise to make a chart like this… • Cellular respiration consists of a sequence of steps that can be divided into three stages. • Stage 1: Glycolysis: break open sugar molecules • Stage 2: Pyruvate oxidation and the citric acid cycle: strip out the electrons • Stage 3: Oxidative phosphorylation: use the electrons to do work/make ATP Electrons carried by Glycolysis Glucose Pyruvate Pyruvate Oxidation Citric Acid Cycle NADH FADH2 Oxidative Phosphorylation (Electron transport and chemiosmosis) MITOCHONDRION CYTOSOL Substrate-level ATP phosphorylation 15 Substrate-level ATP phosphorylation ATP Oxidative phosphorylation As you study each of the 4 steps of cellular respiration, ask these questions: • What goes in? • What comes out? • What happens to the energy that is released? • Where does each step occur? • How is it regulated? 16 4 STEP ONE: GLYCOLYSIS Glycolysis is the process of splitting glucose into pyruvate Glycolysis is the first step of cellular respiration regardless of the presence of oxygen and occurs in the cytoplasm of the cell. “Glyco-” = Sugar “-lysis”= splitting + 2ATP + 2NADH (Involves an enzyme) 17 18 What I want you to know about glycolysis: Glycolysis is divided up into 2 major phasesEnergy investment and Energy Payoff What your textbook says about glycolysis… You are not responsible for memorizing this entire pathway… this year… • Energy Investment • Notice the 2 ATP going in Energy Payoff • • • Notice the 2 NADH molecules Notice the 4 ATP Coming Out Final Product is Pyruvate Glycolysis starts by using two ATP in the energy investment phase (reactions 1–5) • During the energy payoff phase (reactions 6– 10) 2 NADH are made and 4 ATP are produced by substrate-level phosphorylation TOTAL ATP GAINED BY THE CELL IS 2 (-2+4=2) 19 20 5 As glucose is broken down, electrons are loaded onto electron carriers Glucose C6H12O6 Pyruvate C3H4O3 ATP is formed by substrate level phosphorylation during glycolysis • Matter cannot be created or destroyed • There are 12 hydrogens in glucose, but only 8 in the resulting pyruvates. • Those Hydrogens don’t disappear. They are loaded onto electron carriers • (Remember that Hydrogens have 1 proton and 1 electron) H Pyruvate C3H4O3 NAD 21 22 If Oxygen is not present, the NADH made during glycolysis will stay in the cytoplasm and undergo Lactic Acid Fermentation making 2 ATP Glycolysis is regulated by negative feedback inhibition of the enzyme phosphofructokinase • Glycolysis is regulated by negative feedback inhibition: • High levels of ATP (a product of glycolysis) inhibit the third enzyme in the fancy pathway: phosphofructokinase (PFK) • Phosphofructokinase has two binding sites for ATP: active site for reactions and allosteric site for regulation 1. When ATP levels are low, it preferentially binds to the active site and the enzyme catalyzes the third step in glycolysis 2. When ATP levels are high, it binds to a regulatory site and inhibits the enzyme Empty Allosteric site binding site ATP Substrate 23 PFK ATP PFK RXN stops We’ll talk about this more at the end *Note that glycolysis can happen whether there is oxygen present or not* Substrate 24 6 STEP 2 /3 : PYRUVATE OXIDATION AND THE CITRIC ACID CYCLE Study questions for Glycolysis What is the initial reactant(s) necessary for glycolysis to start? Is oxygen necessary for glycolysis? What are the two major phases? What are the 3 final products (name and number) of Glycolysis? What step comes next if there is oxygen? What step comes next if there isn’t oxygen? How is glycolysis regulated? © 2015 Pearson Education, Inc. 25 26 The citric acid cycle: final oxidation of organic molecules Pyruvate is oxidized in preparation for the citric acid cycle • 2 Pyruvate (made during glycolysis) from cytosol à inside mitochondrial matrix • Pyruvate is processed by pyruvate dehydrogenase before entering the citric acid cycle: • a carboxyl group (includes C atom) is removed and given off as Carbon Dioxide • the two-carbon compound remaining is oxidized while a molecule of NAD+ is reduced to NADH • coenzyme A joins with the two-carbon group to form acetyl CoA. The Citric Acid Cycle is also called the Krebs cycle (after the German-British researcher Hans Krebs, who worked out much of this pathway in the 1930s) • completes the oxidation (loss of electrons/H’s)/ breakdown of the glucose molecule in the mitochondria • generates CO2 and many NADH and FADH2 molecules (electron carriers) that will be very important for the ETC/oxidative phosphorylation • Then 2 molecules of acetyl CoA enter the citric acid cycle. Electrons carried by NADH FADH2 Glycolysis Glucose Pyruvate + NADH + H NAD+ Pyruvate Oxidation Citric Acid Cycle 2 Pyruvate CO2 27 MITOCHONDRION CoA Acetyl coenzyme A 1 Oxidative Phosphorylation (Electron transport and chemiosmosis) CYTOSOL 3 Substrate-level ATP phosphorylation Coenzyme A Substrate-level ATP ATP phosphorylation 28 7 What your book says about the Citric Acid Cycle Feeling Daring and Ambitious? Citrate (Citrate) Is (Isocitrate) Krebs'(Ketoglutarate) Starting (Succinyl-CoA) Substrate (Succinate) For(Fumarate) Making (Malate) Oxaloacetate (Oxaloacet ate) Again, you are not responsible for memorizing this entire pathway… this year… 29 PYRUVATE OXIDATION Pyruvate (from glycolysis, 2 molecules per glucose) Acetyl CoA feeds the Citric Acid Cycle • Completes the breakdown of each acetyl CoA • 8 Major Steps in the the cycle. • It takes 2 full turns to consume both Acetyl CoA molecules • One turn of the cycle generates CO2, 1 ATP, 3 NADH, and 1 FADH2. • Two turns generates CO2, 2 ATP, 6NADH, 2 FADH2 • NADH and FADH2 will carry electrons to the electron transport chain, which leads to ATP generation CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA NADH + H+ CoA NAD+ CITRIC ACID CYCLE FADH2 3 NAD+ 3 NADH FAD + 2 H+ ADP + P i ATP 30 The citric acid cycle is regulated by feedback inhibition • The citric acid cycle is regulated by feedback inhibition at multiple points • Reaction rates are high when ATP and NADH are scarce • Rates are low when ATP or NADH is abundant Citric Acid Cycle Study Questions Acetyl CoA CoA Where does this process take place in the cell? What is/are the initial reactant(s) necessary for the citric acid cycle to start? NADH + H+ CoA NAD+ CITRIC ACID CYCLE How many times does it turn per molecule of glucose? FADH2 What are the total final products of the Citric Acid Cycle corresponding to 1 complete glucose molecule? What step comes next? 31 2 CO2 2 CO2 3 NAD+ 3 NADH + 3 H+ FAD ADP + P i ATP 32 8 So what does our net total products look like so far for one starting molecule of glucose? STEP FOUR: OXIDATIVE PHOSPHORYLATION AND THE ELECTRON TRANSPORT CHAIN • NADH and FADH2 are storing most of the energy in the form of highenergy electrons • they take them to an electron transport chain, where ATP will be made. Glycolysis Pyruvate Oxidation 2 ATP 2 NADH 2 NADH CO2 Citric Acid TOTALS 2 ATP 4 ATP 6 NADH 10 NADH 2 FADH2 2 FADH2 CO2 CO2 33 33 34 Making Connections: Does this look familiar? Can you guess how this might work? Oxidative Phosphorylation is comprised of two steps: ETC and Chemiosmosis (It should look familiar) Electron Transport Chain Chemiosmosis 35 36 9 Electrons are delivered to the Electron Transport Chain in the Mitochondria Oxidative Phosphorylation: The Electron Transport Chain NADH/FADH2 deliver electrons to a string of increasingly electronegative protein complexes in the mitochondrial membrane, which moves electrons “down a hill” toward oxygen (most electronegative in the chain). • These protein complexes constitute the electron transport chain in the mitochondria. • Electrons excite the proteins to do work. • At the bottom of the NAD+ hill is oxygen which NADH • accepts two electrons Energy released 2 and available • picks up two H+ for making ATP • becomes reduced to water 2 O2 H2O 2 H+ 37 38 Oxidative Phosphorylation: The Electron Transport Chain • The electron transport chain is a series of protein complexes that are embedded in the inner mitochondrial membrane. • In each complex there are sequentially more and more electronegative molecules, eventually ending with oxygen (the most electronegative molecule) as the final electron acceptor • This produces water, another overall product of cellular respiration. • NADH and FADH2 pass their electrons along this chain of proteins. • This also leads to hydrogen protons being pumped from the matrix to the intermembrane space Electron Transport Chain creates a H+ Gradient with increasing H+ in the intermembrane space Intermembrane Space: Increasing concentration of Hydrogens Hydrogens want to diffuse down their concentration gradient Mito. Matrix: Decreasing concentration of Hydrogens • A protein called ATP synthase provides the main opening for hydrogens in the intermembrane space to PASSIVELY diffuse back through to the matrix. • This diffusion of hydrogen ions across the inner mitochondrial membrane is called chemiosmosis. 39 40 10 ETC and Chemiosmosis Study Questions Chemiosmosis powers the ATP synthase H+ INTERMEMBRANE SPACE • As hydrogen enters the channels in the ATP synthase, they bind to a structure that acts like a rotor. What is/are the initial reactant(s) necessary for the ETC to start? Rotor Does this process require oxygen? Is it aerobic or anaerobic? • This causes it to spin like a water wheel. • This spinning motion causes ADP to bind and receive a phosphate group (phosphorylation) Stator Where does the oxygen position itself and why is this important? Internal rod Describe how the ETC powers ATP production, Catalytic knob • This process makes about 26-28 ATP. What protein ultimately produces ATP? ADP + MITOCHONDRIAL MATRIX Pi ATP 41 42 Anaerobic Respiration Aerobic Respiration is the production of ATP with oxygen as the final electron acceptor • Fermentation is an anaerobic process that cells can use to generate ATP while producing lactic acid or ethanol when oxygen is not available What happens when there is no oxygen available? What we are not covering in this course: • Anaerobic Respiration can occur if an organism uses something else other than oxygen at the bottom of their ETC (like sulfur) 44 Anaerobic Fermentation 48 11 Glycolysis evolved early in the history of life on Earth • Glycolysis is the universal and oldest energy-harvesting process of life. • The ancient history of glycolysis is supported by its • occurrence in all the domains of life (bacteria, fungus, protists, eukaryotes etc) • Occurrence within the cytoplasm only (using pathways that do not involve any membrane-enclosed organelles of the eukaryotic cell) • Fermentation is a way of harvesting chemical energy from pyruvate if oxygen is unavailable/limited or a mitochondria is not present. • Fermentation uses glycolysis and NAD+/NADH to produce 2 ATP and either lactic acid or ethanol Facultative anaerobes • can make ATP by fermentation or oxidative phosphorylation depending on the environment • include yeasts and many bacteria. Clostridium tetani Clostridium botulinum 50 • Fermentation is a way of harvesting chemical energy that does not require oxygen. • Fermentation uses glycolysis like normal 2 ADP +2 2 P ATP Glycolysis Glucose Fermentation enables cells to produce ATP without oxygen 2 NAD+ 2 NADH • produces two ATP molecules per glucose, and reduces NAD+ to NADH • Fermentation provides a mechanism for recycling NADH back to NAD+ called lactic acid fermentation: • NADH is oxidized back to NAD+ • The baking and winemaking industries have used alcohol fermentation for thousands of years. • In this process, yeast (single-celled fungi) • oxidize NADH back to NAD+ • convert pyruvate to CO2 and ethanol Glucose 2 ADP +2 P 2 ATP 2 NAD+ 2 NADH 2 NADH 2 Pyruvate 2 NAD+ • pyruvate is reduced to lactate/lactic acid • Lactate is carried to the liver à converted back to pyruvate à oxidized in the mitochondria if oxygen becomes available Fermentation enables cells to produce ATP without oxygen 2 Pyruvate • It can then be used to breakdown available glucose again 51 Obligate anaerobes • require anaerobic conditions • are poisoned by oxygen • live in stagnant ponds and deep soils Glycolysis 49 Some Prokaryotic Organisms rely on Anaerobic Fermentation to produce Energy 2 CO 2 2 NADH 2 NAD+ 2 Lactate Overall: Fermentation is much less efficient than cellular respiration. It only produces 2 ATP per glucose, while oxidative phosphorylation yields about 29-32 ATP per glucose 2 Ethanol 52 12 Chapter Recap 55 13