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INTRODUCTION TO CELLULAR RESPIRATION Photosynthesis and Cellular Respiration Provide Energy For Life Energy is necessary for life processes (growth, transport, manufacture, movement, reproduction, etc.) Energy that supports life on Earth is captured from sun and used for plant, algae, protist, and bacterial photosynthesis Photosynthesis produces ___________ and __________. Other organisms use the O2 and energy in sugar and release CO2 and H2O Together, these two processes are responsible for the majority of life on Earth Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts CO2 Glucose + + H2O O2 Cellular respiration in mitochondria ATP (for cellular work) Heat energy Breathing Supplies Oxygen to Our Cells For Use in Cellular Respiration and Removes Carbon Dioxide Breathing and cellular respiration are closely related – Breathing is necessary for exchange of CO2 produced during cellular respiration for atmospheric O2 – Cellular respiration uses O2 and produces CO2 O2 Breathing CO2 Lungs CO2 Bloodstream Muscle cells carrying out Cellular Respiration Glucose + O2 CO2 + H2O + ATP O2 Cellular Respiration Banks Energy in ATP Molecules Cellular respiration is an exergonic process that transfers energy from the bonds in glucose to ATP Cellular respiration produces 38 ATP/glucose molecule C6H12O6 Glucose + 6 O2 Oxygen 6 CO2 Carbon dioxide + 6 H2O Water + ATPs Energy Other foods (organic molecules) can be used as a source of energy as well Cells Tap Energy From Electrons “falling” From Organic Fuels to Oxygen When the bonds of glucose are broken, electrons are ultimately transferred to oxygen Oxygen is electronegative, and pulls e- towards it Cellular respiration is the controlled breakdown of organic molecules Energy is released in small amounts, and stored in ATP NADH NAD+ + ATP 2e– Controlled release of energy for synthesis of ATP H+ 2e– H+ H 2O 1 2 O2 Cells Tap Energy From Electrons “falling” From Organic Fuels to Oxygen The cellular respiration equation explained: – Glucose loses its hydrogen (and electrons) atoms and is ultimately converted to CO2 – At the same time, O2 gains hydrogen atoms (and electrons) and is converted to H2O – Loss of electrons is called oxidation – Gain of electrons is called reduction – The reducing agent = The molecule carrying the hydrogens (e-) (NADH, FADH2) – The oxidizing agent= The molecule that receives the hydrogens (e-) (NAD+, FAD) Loss of hydrogen atoms (oxidation) C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP) Glucose Gain of hydrogen atoms (reduction) Enzymes are necessary to Oxidize Glucose and Other Foods The enzyme that removes hydrogen from an organic molecule is called dehydrogenase Oxidation Dehydrogenase Reduction NAD+ + 2H 2 H+ + 2 e– + NADH + H (carries 2 electrons) Cells tap energy from electrons “falling” from organic fuels to Oxygen – Dehydrogenase requires a coenzyme called NAD+ (nicotinamide adenine dinucleotide) to carry e– Another coenzyme that functions like NAD+ is FAD – They “carry” e- from glucose to a series of proteins found along the cristae of the mitochondrion called the electron transport chain or ETC Copyright © 2009 Pearson Education, Inc. STAGES OF CELLULAR RESPIRATION AND FERMENTATION Cellular respiration occurs in three main stages Stage 1: Glycolysis – Occurs in the cytoplasm – What happens ?: A single molecule of glucose is enzymatically cut in half through a series of steps to produce two molecules of pyruvate – In addition to Pyruvate, other products are: – – Two molecules of NADH (when two molecules of NAD+ are reduced) Two molecules of ATP, produced by substrate-level phosphorylation Substrate-level Phosphorylation Substrate level phosphorylation is when an enzyme transfers a phosphate group from a substrate molecule to ADP, forming ATP Enzyme P Enzyme + ADP ATP P Substrate P Product ENERGY INVESTMENT PHASE Glucose ATP Steps 1 – 3 A fuel molecule is energized, using ATP. Step 1 ADP P Glucose-6-phosphate P Fructose-6-phosphate P Fructose-1,6-bisphosphate 2 ATP 3 ADP P Step 4 A six-carbon intermediate splits Into two three-carbon intermediates. 4 P Step 5 A redox reaction generates NADH. Glyceraldehyde-3-phosphate (G3P) P NAD+ NAD+ 5 P NADH 5 NADH + H+ ENERGY PAYOFF PHASE P + H+ P P ADP P P 1,3-Bisphosphoglycerate ADP 6 6 ATP ATP P P 3-Phosphoglycerate 7 Steps 6 – 9 ATP and pyruvate are produced. 7 P P 2-Phosphoglycerate 8 H2 O P P ADP Phosphoenolpyruvate (PEP) ADP 9 ATP 8 H2 O 9 ATP Pyruvate Pyruvate is chemically groomed for the citric acid cycle Grooming Step: Location: mitochondrial matrix Purpose: to prepare pyruvate for entry into the Kreb’s cycle What Happens?: There are three steps – 1. The removal of a carboxyl group released as CO2 (decarboxylation) – 2. Oxidization of the remaining 2-carbon compound to form acetate – 3. Coenzyme A binds to the 2-carbon fragment forming acetyl coenzyme A • Products are CO2 , Acetyl CoA, and NADH NADH + H+ NAD+ 2 CoA Pyruvate Acetyl coenzyme A 1 3 CO2 Coenzyme A Cellular respiration occurs in three main stages Stage 2: The Kreb’s Cycle (citric acid cycle) – Location: mitochondrial matrix – Purpose: Breaks down pyruvate into CO2 and supplies ETC with electrons (via NADH, FADH2) – What Happens?: 2-C acetate combines with 4-C oxaloacetate forming 6-C citrate – 6-C citrate then passes through a series of redox reactions that regenerate oxaloacetate (4-C molecule ) – Glucose is completely oxidized in this phase – For one turn of the cycle products are 3 NADH, 1 FADH2 , 1 ATP (by SLP), 2 CO2 Acetyl CoA CoA CoA CITRIC ACID CYCLE 2 CO2 3 NAD+ FADH2 3 NADH FAD 3 H+ ATP ADP + P CoA Acetyl CoA CoA 2 carbons enter cycle Oxaloacetate 1 Citrate NADH + H+ NAD+ 5 NAD+ 2 NADH + H+ CITRIC ACID CYCLE CO2 leaves cycle Malate ADP + P FADH2 4 ATP FAD Alpha-ketoglutarate 3 CO2 leaves cycle Succinate NADH + H+ Step 1 Acetyl CoA stokes the furnace. NAD+ Steps 2 – 3 NADH, ATP, and CO2 are generated during redox reactions. Steps 4 – 5 Redox reactions generate FADH2 and NADH. Cellular respiration occurs in three main stages Stage 3: Oxidative phosphorylation (aka the ETC) – Location: cristae of mitochondrion – Purpose: to generate a proton gradient that will be used to form ATP – What Happens?: Electrons are supplied by NADH & FADH2 , then – – – – shuttled through the ETC. As e- are transported from protein to protein, H+ are concentrated in the intermembrane space The potential energy of this proton gradient is used to make ATP by chemiosmosis The concentration gradient drives H+ through ATP synthases producing ATP The ETC + chemiosmosis = oxidative phosphorylation Products: 34-38 ATP/glucose Intermembrane space Protein complex of electron carriers H+ H+ H+ H+ H+ H+ H+ Electron carrier H+ H+ ATP synthase Inner mitochondrial membrane FADH2 Electron flow NADH Mitochondrial matrix FAD NAD+ H+ 1 2 O2 + 2 H+ H+ H+ H2O Electron Transport Chain OXIDATIVE PHOSPHORYLATION ADP + P ATP H+ Chemiosmosis Electron shuttle across membrane Cytoplasm 2 NADH Mitochondrion 2 NADH (or 2 FADH2) 6 NADH 2 NADH GLYCOLYSIS Glucose 2 Pyruvate 2 Acetyl CoA + 2 ATP by substrate-level phosphorylation Maximum per glucose: CITRIC ACID CYCLE + 2 ATP by substrate-level phosphorylation About 38 ATP 2 FADH2 OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) + about 34 ATP by oxidative phosphorylation Fermentation enables cells to produce ATP without oxygen Fermentation is an anaerobic (without oxygen) energy- generating process – Includes glycolysis, and the regeneration of NAD+ – Purpose: to produce ATP in the absence of oxygen – What Happens?: NADH is oxidized to NAD+ when pyruvate is reduced to lactate – Pyruvate serves as an “electron sink,” a place to dispose of the electrons generated by oxidation reactions in glycolysis – Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation Copyright © 2009 Pearson Education, Inc. 2 ADP +2 P Glycolysis 2 ATP GLYCOLYSIS Glucose 2 NAD+ 2 NADH Lactic Acid Fermentation 2 Pyruvate 2 NADH Steps to regenerate NAD+ 2 NAD+ 2 Lactate Lactic acid fermentation Fermentation enables cells to produce ATP without oxygen The baking and winemaking industry have used alcohol fermentation for thousands of years – Happens in yeast cells (single-celled fungi) – They convert pyruvate to CO2 and ethanol while oxidizing NADH back to NAD+ 2 ADP +2 P Glycolysis 2 ATP GLYCOLYSIS Glucose 2 NAD+ 2 NADH 2 Pyruvate 2 NADH Steps to regenerate NAD+ with a release of CO2 2 CO2 released 2 NAD+ 2 Ethanol Alcohol fermentation Alcohol Fermentation The Human Body Uses Energy From ATP for All Its Activities The average adult human needs about 2,200 kcal of energy per day – A kilocalorie (kcal) is the quantity of heat required to raise the temperature of 1 kilogram (kg) of water by 1oC INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS Cells use many kinds of organic molecules as fuel for cellular respiration Although glucose is considered the primary source of sugar for respiration and fermentation, there are actually three sources of molecules for generation of ATP – Carbohydrates (disaccharides) – Proteins (after conversion to amino acids) – Fats Food, such as peanuts Carbohydrates Fats Glycerol Sugars Proteins Fatty acids Amino acids Amino groups Glucose G3P Pyruvate GLYCOLYSIS Acetyl CoA ATP CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) ATP needed to drive biosynthesis ATP CITRIC ACID CYCLE GLUCOSE SYNTHESIS Acetyl CoA Pyruvate G3P Glucose Amino groups Amino acids Proteins Fatty acids Glycerol Fats Cells, tissues, organisms Sugars Carbohydrates Cellular respiration generates has three stages oxidizes uses ATP produce some (a) C6H12O6 energy for produces many (b) (d) to pull to electrons down (c) by process called uses H+ diffuse through ATP synthase uses (e) pumps H+ to create (f)