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Transcript
Intensive Biology Chapter 6: Cellular Respiration Worksheet Cellular Respiration Cells do lots of work - anabolism, transport, movement, growth, reproduction, etc. They need energy to fuel this work. Cells store potential energy in the arrangement of the atoms in macromolecules. Cells use energy in the form of ATP. A cell must regenerate its supply of ATP. Working muscles use ATP at a rate of 10 million molecules per second. Cellular respiration converts the potential energy stored in macromolecules to the usable energy of ATP. Metabolism – all chemical activity of a cell Anabolism = synthesis = building larger molecules – endothermic reactions = require energy Catabolism = decomposition = breaking down molecules – exothermic reactions = release energy Oxidation - partial or complete loss of electron(s) (NADH to NAD+) Reduction - partial or complete gain of electron(s) (NAD+ to NADH) Reducing agent (compounds that get oxidized)- electron donor C6H12O6, FADH2, NADH Oxidizing agent (compounds that get reduced)- electron acceptor Oxygen, FADH+, NAD+ In general, organic molecules that have an abundance of C-H bonds are a source of electrons with the potential to fall (move) closer to Oxygen. Potential Energy = Bonds = Position of Electrons An electron loses potential energy when it shifts from a less electronegative atom (atom that doesn’t like electrons as much) toward a more electronegative atom (atom that likes electrons more). A redox reaction relocates electrons closer to oxygen (or another oxidizing agent) releasing chemical energy that can be put to work. 1 Aerobic respiration – in presence of oxygen. Anaerobic respiration – absence of oxygen (glycolysis + fermentation) Summary equation for aerobic cellular respiration ----------Oxidation---------- C6H12O6 + 6O2 --------- 6CO2 + 6H2O + Energy ------------Reduction------- Cellular respiration converts the potential energy stored in macromolecules to the usable energy of ATP. In effect, they "cash in the large denomination of energy banked in glucose for the small change of ATP, which is more practical for the cell to spend on its work." ELECTONS TRAVEL DOWNHILL VIA Food ------------NADH -------------Electron Transport Chain-----------Oxygen TWO WAYS ATP IS GENERATED: 6.7 Two mechanisms generate ATP • Cells use the energy released by “falling” electrons to pump H+ ions across a membrane – The energy of the gradient is harnessed to make ATP by the process of chemiosmosis High H+ concentration ATP synthase uses gradient energy to make ATP Membrane Electron transport chain ATP synthase Energy from Low H+ concentration Figure 6.7A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • ATP can also be made by transferring phosphate groups from organic molecules to ADP – This process is called substrate-level phosphorylation Enzyme Adenosine Organic molecule (substrate) Adenosine New organic molecule (product) Figure 6.7B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 Cellular Respiration Overview I. Glycolysis - occurs outside of the mitochondrion in cytosol. II. Transition Reactions - occurs in the Mitochondrial Matrix III. Krebs Cycle (Citric Acid Cycle) - occurs in the Mitochondrial Matrix IV. Electron Transport Chain (Oxidative Phosphorylation) - built into membrane of the cristae 3 I. GLYCOLYSIS Glycolysis harvests chemical energy by breaking down glucose to pyruvate (pyruvic acid) 4 WHERE IT OCCURS: OVERALL PROCESS: GLYCOLYSIS END PRODUCTS: WHAT YOU START WITH: FERMENTATION: 5 FERMENTATION Glycolysis in and of itself is not a very effective means of tapping all the energy stored in glucose. Most of the energy is still stuck in the 2 molecules of pyruvate. Under aerobic conditions (oxygen is present) the pyruvate will enter the Krebs Cycle. Under anaerobic conditions (no oxygen present) glycolysis would quickly deplete the cell of NAD+. However, if there is no oxygen present, a cell may use the process of fermentation. FERMENTATION = glycolysis plus reactions that regenerate NAD+ Alcohol fermentation - Lactic Acid Fermentation - In absence of oxygen, get regeneration of NAD+ thru fermentation Realize that some animals (particularly many bacteria) live in anaerobic environments or habitats with very little oxygen. Glycolysis is their main way to get ATP. Glycolysis only produces 2 ATP's by itself (for every molecule of glucose), but when coupled with the Krebs Cycle and Electron Transport Chain, each molecule of glucose decomposed can produce 36-38 ATP's! That's a huge difference. In presence of oxygen, potential energy of 2NADH gets shuttled over to electron transport chain. Further, the 2 pyruvate molecules can get broken down to tap their potential energy in the Krebs cycle. 6 II. INTERMEDIATE STAGE Transition (Intermediate) Reactions Before pyruvate enters Krebs Cycle, it must enter the mitochondria via a transport protein. Then the pyruvate: 1. 2. 3. The 2 acetylCoA molecules can now enter the Krebs Cycle. 7 III. THE KREBS CYCLE (Citric Acid Cycle) Keep in mind that: • for every glucose molecule split during glycolysis, two acetyl CoA molecules are produced; therefore, • it takes two turns of Krebs Cycle to complete the breakdown of glucose. WHERE IT OCCURS: OVERALL PROCESS: KREB CYCLE END PRODUCTS: WHAT YOU START WITH: 8 IV. ELECTRON TRANSPORT CHAIN Every NADH that enters the electron transport chain will yield approximately 3 ATP molecules. Every FADH2 that enters the electron transport chain will yield approximately 2 ATP molecules. ETC: TWO MAJOR EVENTS: 1. Passing of electrons 9 2. Pumping of H+ ions Those H+ ions can then diffuse down their concentration gradient through ATP Synthase a protein complex embedded in the inner membrane which uses the energy of the H+ gradient to drive ATP synthesis. This process of harnessing the energy of H+ ions diffusion down there concentration gradient to power the synthesis of ATP is called Chemiosmosis ETC START WITH: END PRODUCTS: 10 11