Lecture 07 Objectives At the end of this series of lectures, you should be able to: Define terms. Compare the processes and locations of cellular respiration and photosynthesis. Explain how breathing and cellular respiration are related. Provide the overall chemical equation for cellular respiration. Explain how the energy in a glucose molecule is released during cellular respiration. 1
Objectives List the cellular regions where glycolysis, the citric acid cycle, and oxidative phosphorylation occur. Compare the reactants, products, and energy yield of the three stages of cellular respiration. Describe the overall process of cellular respiration. Compare the reactants, products, and energy yield of alcohol and lactic acid fermentation. Energy for Life Most energy for life is captured as solar energy by photosynthesis. For most organisms that energy is converted to the usable form (ATP) by cellular respiration. 2
Mikael Häggström, CC BY SA 3.0, http://en.wikipedia.org/wiki/cellular_respiration#mediaviewer/file:auto and_heterotrophs.png 6CO 12H O Light C H O 6O 6H O C H O 6O 6CO 6H O 32 ATP Heat 3
Respiration Breathing inspiration (bringing air in) expiration (moving air out) External respiration Internal respiration Cellular respiration 6 6 6 32 4
Overview Concepts Glucose can be burned and the energy released. Not biologically useful. Cellular respiration is the controlled release of energy from glucose. Some of the energy is captured in a biologically useful way. Movement of electrons in oxidation reduction (redox) reactions. Overview Concepts Oxidation Reduction Reactions Oxidation The loss of electrons from a substance Reduction The addition of electrons to a substance These reactions occur in pairs One reaction donates the electrons and the other accepts the reactions. In biological reactions, you cannot see the electrons, but you can see hydrogen move which represents electron transfers. 5
Cameron Garnham, CC BY SA 3.0, http://commons.wikimedia.org/wiki/file:redox_reminder.png Overview Concepts NADH Coenzymes NAD + accepts electrons and becomes reduced NADH Moves electrons in a controlled manner from one reaction to another. 6
Overview Concepts Electron Transport Chains Electron transport chains are a series of carrier molecules that accept the electrons and move them down an energy gradient in a controlled fashion. The movement of the electrons causes H + to be pumped one side of the membrane to the other. This creates a gradient of H +. The movement of H + back across the membrane is used to synthesize ATP. O 2 is the final electron acceptor makes H 2 O Stages Glycolysis Pyruvate Oxidation and Citric Acid Cycle (Krebs Cycle) Oxidative phosphorylation (Electron Transport Chain) 7
OpenStax College, CC BY 3.0, http://cnx.org/contents/9d68abf9 4c2e 4ef7 88d1 c963c5c844b9@3 Glycolysis Occurs in the cytoplasm (cytosol) Breaks (lyses) glucose into 2 3 carbon compounds pyruvate. Requires an investment of ATP Produces 2pyruvate, 2 ATP and 2 NADH 8
Biology by OpenStax College is licensed under a Creative Commons Attribution 3.0 Glycolysis Glucose (C 6 ) + 2 ADP + 2 P i + 2 NAD + 2 ATP + 2 NADH + 2 Pyruvate (C3) 9
Glycolysis Substrate level phosphorylation One method by which ATP is formed Occurs in other reactions also Passes a phosphate directly to ADP to form ATP Requires appropriate enzyme Pyruvate Oxidation Occurs in the matrix of the mitochondria Breaks the pyruvates into 2 carbon compound (Acetyl CoA). Requires coenzyme A (CoA) Produces CO 2 waste product Produces 2 Acetyl CoA and NADH 10
Biology by OpenStax College is licensed under a Creative Commons Attribution 3.0 Pyruvate Oxidation 2 Pyruvate (C3) + 2 O2 + 2 NAD + + 2 CoA 2 CO2 + 2 NADH + 2 Acetyl CoA (C 2 ) 11
Citric Acid Cycle Also called the Krebs Cycle Occurs in the matrix of the mitochondria Completes the breakdown of glucose (Acetyl CoA) into CO 2 waste product Produces 2ATP, 6NADH, and 2FADH 2 from each glucose (2 turns of the cycle) Citric Acid Cycle 2 Acetyl CoA + 4 O2 + 6 NAD + + 2 ADP + 2 P i + 2 FAD +2 4 CO2 + 6 NADH + 2 ATP + 2 FADH2 12
Biology by OpenStax College is licensed under a Creative Commons Attribution 3.0 Oxidative Phosphorylation Occurs on the cristae of the mitochondria Accepts electrons from NADH and FADH 2 Produced in glycolysis, pyruvate oxidation, and citric acid cycle. Uses electron transport chains to generate ATP Produces ~28 ATP 13
Oxidative Phosphorylation Chemiosmosis Uses energy stored in a hydrogen ion gradient to drive ATP synthesis. Occurs on the cristae of the mitochondria. Oxidative Phosphorylation 7 O2 + 28 ADP + 28 P i + 10 NADH + 2 FADH2 28 ATP + H2 O + 10 NAD + + 2 FAD +2 14
Fvasconcellos, Public Domainhttp://en.wikipedia.org/wiki/Oxidative_phosphorylation#mediaviewer/File:Mitochondrial_electron_transport_chain%E2%80%94Etc4.svg Each glucose molecule results in the production of about 32 ATP. Glycolysis: 2 ATP Citric Acid Cycle: 2 ATP Oxidative Phosphorylation: 28 ATP About 34% of the glucose s potential energy 15
Anaerobic Respiration Fermentation Occurs in the absence of oxygen Glycolysis does not require oxygen so it can still produce its 2 ATP per glucose. Need to regenerate NAD + to continue accept electrons Other steps in cellular reaction require oxygen so they will not occur without oxygen. Reduced efficiency Anaerobic Respiration Lactic Acid Fermentation A process for regenerating NAD + Occurs in muscle cells and certain bacteria Pyruvate is converted to lactate (lactic acid) Lactate is carried via the blood to the liver where, if there is enough oxygen, it is converted back to pyruvate. Bacteria are use this technique to produce yogurt, cheese, soy sauce, and sauerkraut. 16
Darekk2, CC BY SA 3.0, http://en.wikipedia.org/wiki/cellular_respiration#mediaviewer/file:cellular_respiration.gif Anaerobic Respiration Alcohol Fermentation A process for regenerating NAD + Occurs with some yeast (fungi) Pyruvate is converted to CO 2 and ethanol Ethanol is toxic 17
Darekk2, CC BY SA 3.0, http://en.wikipedia.org/wiki/cellular_respiration#mediaviewer/file:cellular_respiration.gif Other Metabolic Pathways Other organic molecules can be used as fuel for cellular respiration. Other macromolecules enter cellular respiration at different points. Fats generate more ATP than an equal mass of carbohydrates. Proteins produce relatively little ATP Produces more waste (amine groups) disposed of by urine 18