Cellular Respiration PDF

Bioenergetics (Chapters 3, 5, 6)  Energy  Cellular Respiration  Photosynthesis Bioenergetics Light energy Photosynthesis in chloroplasts CO2 + H2O Organic + O...

Bioenergetics (Chapters 3, 5, 6)  Energy  Cellular Respiration  Photosynthesis Bioenergetics Light energy Photosynthesis in chloroplasts CO2 + H2O Organic + O 2 molecules ECOSYSTEM Cellular respiration in mitochondria ATP Powers most cellular work Heat energy Cellular Respiration - Energy derived from food Aerobe - organism that grows or metabolizes only in the presence of oxygen (plants and animals). Anaerobe - organism that grows only in the absence of oxygen (sulphate-reducing bacteria). Facultative anaerobe - organism capable of carrying out aerobic respiration but able to switch to fermentation when oxygen is unavailable (E. coli and yeast). Cellular respiration - the process by which cells generate ATP through a series of redox reactions; electrons are removed from various molecules such as glucose and passed through intermediate electron carriers to a final electron acceptor.  When this acceptor molecule is oxygen, the process is called aerobic respiration.  When it is a chemical substance (inorganic molecule) in the absence of oxygen, the process is called anaerobic respiration.  When it is an organic molecule, the process is called fermentation. During aerobic cellular respiration, the fuel (such as glucose) is oxidized and oxygen is reduced. Cellular respiration can be summarized as the following equation: becomes oxidized C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes reduced Mitochondrion - structure and function - the power station of the cell, an organelle in eukaryotic cells where cellular respiration and ATP synthesis occur. Double-membrane mitochondrion forms two different compartments:  Outer membrane  Inner membrane Inner Outer  Intermembrane space Matrix Cristae membrane membrane  Matrix  Folds (cristae) Aerobic Respiration - a redox process Most cells of plants, animals, protists, fungi, and bacteria use aerobic respiration to gain energy from glucose. The overall reaction pathway for the aerobic respiration of glucose is summarized as follows: C6H12O6 + 6 O2 + 6 H2O 6 CO2 + 12 H2O + Energy* Oxidation C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy* Reduction Energy - in the chemical bonds of ATP Aerobic respiration involves four stages:  Glycolysis  Formation of acetyl-CoA  Krebs cycle  Electron transport chain/Chemiosmosis  Cellular Respiration: an overview of glucose metabolism Glucose Pyruvate  glycolysis takes place FINAL - > in the cutosome. Glycolysis (glycos, sugar and lysis, dissolution) - the multistep chemical breakdown of a 6-C glucose molecule into two, 3-C molecules of pyruvate. An overview of glycolysis: harvesting chemical energy by oxidizing glucose to pyruvate Glycolysis - The first phase includes endergonic reactions requiring an investment of ATP. Energy Investment Phase Glycolysis - The second phase includes exergonic reactions yielding ATP and NADH. Energy Liberation Phase Glycolysis  The first stage of cellular respiration in all organisms.  Occurs in the cytoplasmic fluid.  An ancient and universal metabolic system does not require oxygen.  Starting materials: glucose, ADP+Pi, NAD+, ATP and enzymes.  Produces 2 pyruvate, 2 ATP and 2 NADH.  Consists of a series of reactions divided into two major phases with 10 steps, each of which is catalyzed by a specific enzymes: o The first phase includes endergonic reactions requiring an investment of ATP. o The second phase includes exergonic reactions yielding ATP and NADH. Formation of Acetyl-CoA - the conversion of pyruvate to acetyl-CoA Grooming pyruvate/pyruvate decarboxylation  Occurs in mitochondria.  A carbon atom in pyruvate is removed and released in CO2.  A coenzyme-A (CoA) is attached.  An acetyl-CoA is produced.  A molecular of NAD+ is reduced to NADH (total 2 NADH).  The reaction is catalyzed by pyruvate dehydrogenase. Kreb’s Cycle (Citric Acid Cycle; tricarboxylic acid (TCA) cycle) - the metabolic cycle that is fueled by acetyl-CoA formed after glycolysis in cellular respiration; chemical reactions in the Krebs cycle complete the metabolic breakdown of glucose molecules to CO2. The cycle was finally identified in 1937 by Hans Adolf Krebs who received the Nobel Citric acid Prize for Physiology or Medicine in 1953 An overview of the TCA cycle: completing the energy-yielding oxidation of organic molecules Kreb’s Cycle ATP Kreb’s Cycle (citric acid cycle; tricarboxylic acid cycle)  Occurs in the matrix of mitochondria.  The four-carbon molecule oxaloacetate accepts two-carbon acetyl group from acetyl-CoA.  The first product as citric acid.  Includes eight steps each of which is catalyzed by a specific enzyme.  The cycle completely disassembles acetyl-CoA, stripping away its electrons and producing CO2.  At the end of each cycle, the oxaloacetate has been regenerated.  High energy extraction steps produce 2 ATP, 6 NADH and 2 FADH2 per a glucose molecule.  NADH and FADH2 molecules carry most of the energy (in the form of high-energy electrons) of the original glucose molecule to the electron transport chains. Electron Transport Chain (the respiratory chain) - a sequence of electron-carrier molecules that shuttle electrons during redox reactions, with the release of energy. Electron Transport Chain  The electron transport chain is embedded in the inner 50 NADH mitochondrial membrane (comparable to bacterial FADH2 plasma membrane). Free energy (G) relative to O2 (kcal/mol) Multiprotein 40 FMN I FAD complexes  The chain contains three (four) large enzyme Fe S Fe S II Q complexes and several (mobile) electron carriers: Cyt b III 30 Fe S I NADH-Q reductase complex Cyt c1 IV Cyt c II (Succinate-Q reductase complex) Cyt a Cyt a3 III Cytochrome b/c1 reductase complex 20 IV Cytochrome c oxidase complex 10 Flavin mononucleotide (FMN) Ubiquinone (Q) 0 2 H+ + 1/2 O2 Cytochrome (b, c, c1, a, a3) H2O Electron Transport Chain  All of the carriers can exist in an oxidized form or reduced form, bind and release electrons in redox reactions. The relationship between free energy and electron movement along the electron transport chain  The electrons from NADH or FADH2 entering the electron transport chain have a relatively high energy content, and lose Intermembrane some of their energy at each step as they pass along the chain. space FADH2  As redox occurs, the electron carriers use some of the energy FAD+ released as electrons pass down the electron transport chain to actively transport proton (hydrogen ion, H+) from one side of the inner mitochondrial membrane to the other, which results in an H+ gradient.  In the end, the electrons are simultaneously united with H+ from the surrounding medium to form hydrogen which reacts with oxygen (O2) to produce water. Matrix  NADH and FADH2 are the primary electron donors.  O2 is the final electron acceptor.  During oxidative phosphorylation, chemiosmosis Chemiosmosis couples electron transport to ATP synthesis - the production of ATP using the energy of proton gradient across membranes to phosphorylate ADP; it powers the most ATP synthesis in cells.  The activity of electron transport chains establishes the proton gradient between the intermembrane space and the matrix.  The proton gradient is a form of potential energy that can be harnessed to provide the energy for ATP synthesis.  Diffusion of protons from the intermembrane space through the inner mitochondrial membrane to the matrix is through specific channels formed by an enzyme complex, ATP synthase.  Diffusion of the protons down their gradient, through the ATP synthase complex, is an exergonic process.  This exergonic process drives the endergonic reaction, in which ATP is produced by phosphorylating ADP - oxidative phosphorylation. Oxidative Phosphorylation Mitochondria are called the power plants of the cell because most of a cell's ATP is produced there in the process of oxidative phosphorylation. ATP synthase a b ATP synthase complex from mitochondria. (a) electron micrographs showing the knoblike protrusions from the mitochondrial inner membrane. (b) schematic diagram showing the likely organization of the subunits to form the proton-conducting F0 portion, and the ATP-synthesizing F1 unit (Efraim Racker in the early 1960s) Aerobic Respiration of One Glucose Yields a Maximum of 36 to 38 ATPs Glycolysis -- 2 ATP + 2 NADH Pyruvate grooming -- 2 NADH Total: 4 ATP, 10 NADH and 2 FADH2 Kreb’s cycle -- 2 ATP + 6 NADH + 2 FADH2  The oxidation of NADH in the electron transport chain yields up to 3 ATPs. However, the 2 NADH molecules produced through glycolysis in the cytosol yields either 2 ATPs (eukaryotes) or 3 ATPs (prokaryotes). Thus, the maximum number of ATPs formed using the energy from NADH is 28 to 30.  The oxidation of FADH2 yields 2 ATPs per molecule, so the 2 FADH2 molecules produced in the Kreb’s cycle yield 4 ATPs. https://youtu.be/q-fKQuZ8dco ATP yield per molecule of glucose at each stage of cellular respiration Other Organic Molecules as Fuels Carbohydrates -- glucose and other sugars. Entering glycolysis Proteins -- amino acids. e.g. alanine - pyruvate glutamate - ketoglutarate aspartate - oxaloacetate Fats -- glycerol + fatty acids. glycerol - glycerol 3-phosphate fatty acids - acetyl-CoA Each gram of sugars or amino acids has about 4 kcal Each gram of proteins in the diet contains 4 kcal Each gram of lipid in the diet contains 9 kcal Cellular utilization of carbohydrates, proteins and fats Fermentation - An ATP-generating process in which organic compounds act as both donors and acceptors of electrons; occurs in the absence of O2.  Some organisms are able to survive without O2.  Organisms survive on the energy base of two molecules of ATP per glucose molecule that come from glycolysis by substrate-level phosphorylation.  Excess cytosolic NADH produced during glycolysis tends to be toxic to the cells.  In fermentation, NADH molecules transfer their hydrogen atoms to organic molecules, thus regeneration of the NAD+ enables cells to keep glycolysis going. Fermentation – Anaerobic Respiration Alcoholic fermentation - yeasts and certain bacteria convert the pyruvate produced by glycolysis to CO2 and ethanol. Lactic acid fermentation - in some fungi and bacteria, lactic acid, rather than alcohol, is 1 produced when NADH from glycolysis is 2 oxidized.  Lactic acid fermentation is used in the dairy 1 pyruvate decarboxylase industry to make cheese and yogurt. 2 alcohol dehydrogenase  Human muscle cells can also make ATP by this metabolic pathway when oxygen is scarce. Functions of fermentation:  It is an inefficient way to use fuel.  It allows organisms to survive without oxygen. 1  It removes toxic excess NADH in the cytosol.  It replenishes the supply of NAD+. 1 lactate dehydrogenase