Respiration • Cellular respiration is the process by which cells transfer chemical energy from sugar molecules to ATP molecules. • As this happens cells.
Download ReportTranscript Respiration • Cellular respiration is the process by which cells transfer chemical energy from sugar molecules to ATP molecules. • As this happens cells.
Respiration • Cellular respiration is the process by which cells transfer chemical energy from sugar molecules to ATP molecules. • As this happens cells release CO2 and use up O2 • Respiration can be AEROBIC or ANAEROBIC Breathing supplies oxygen to our cells and removes carbon dioxide – Breathing provides for the exchange of O2 and CO2 Between an organism and its environment O2 CO2 Breathing Lungs CO2 Bloodstream O2 Muscle cells carrying out Cellular Respiration Glucose + O2 Figure 6.2 CO2 + H2O + ATP The human body uses energy from ATP for all its activities. – ATP powers almost all cellular and body activities . CELLULAR RESPIRATION • Cellular respiration is an energy- releasing process. It produces ATP • ATP is the universal energy source Making ATP • Plants make ATP during photosynthesis • Cells of all organisms make ATP by breaking down carbohydrates, fats, and protein – The energy in an ATP molecule • Lies in the bonds between its phosphate groups Adenosine Adenosine diphosphate Triphosphate Phosphate groups P Adenine P P H2O P Hydrolysis Ribose ATP Figure 5.4A ADP P + P + Energy REDOX REACTIONS – The loss of electrons is called oxidation. – The addition of electrons is called reduction Overview of Aerobic Respiration C6H12O6 + 6O2 6CO2 + 6H2O +ATP glucose oxygen carbon dioxide water – When glucose is converted to carbon dioxide • It loses hydrogen atoms, which are added to oxygen, producing water Loss of hydrogen atoms (oxidation) C6H12O6 + 6 O2 6 CO2 Glucose 6 H2O + Energy (ATP) Gain of hydrogen atoms (reduction) Figure 6.5A + STAGES OF CELLULAR RESPIRATION Overview: Cellular respiration occurs in three main stages 1. Glycolysis 2. Krebs Cycle or Citric Acid Cycle 3. Electron Transport Chain or Phosphorylation – Stage 1: Glycolysis – No oxygen needed. It is universal • • Occurs in the cytoplasm Breaks down glucose into pyruvate, producing a small amount of ATP (2) GLYCOLYSIS • Where?: In the cytosol of all cells. Both aerobic and anaerobic respiration begin with glycolysis. • What happens?: The cell harvests energy by oxidizing glucose to pyruvate. • One molecule of glucose (6 carbons) is converted to two pyruvate molecules (3 carbons) through a series of 10 reactions mediated by enzymes. • Result: 2 pyruvate molecules (each with a 3 carbon backbone) 2 NADH molecules. Carrier that picks up hydrogens stripped from glucose. 2 ATP molecules. 4 are made but cells use 2 to start glycolysis so net gain is 2 An overview of cellular respiration Preparatory steps to enter the Krebs cycle • The 2 pyruvate molecules enter the mitochondrion and an enzyme strips one carbon from each pyruvate. • This two carbon molecule is picked up by Coenzyme A in preparation for the Krebs cycle. • This is acetyl CoA. This is what enters the Krebs cycle: C-C-CoA (oxaloacetate) Stage 2 : The citric acid cycle or Krebs cycle • • • • Takes place in the mitochondria Completes the breakdown of glucose (catabolism), producing a small amount of ATP (2ATP) Pyruvate is broken down to carbon dioxide More coenzymes are reduced .Supplies the third stage of cellular respiration with electrons (hydrogen carriers such as NADH) KREBS CYCLE or citric acid cycle • This cycle involves a series of 8 steps forming and rearranging. Each time it releases CO2 and NADH carries hydrogen to the last step. 6 CO2 are given off as waste (this is the most oxidized form of Carbon) In total: 6 CO2 6 NADH are produced and 2 FADH and only 2 ATP An overview of cellular respiration Stage 3: Oxidative phosphorylation or electron transport chain • • • Occurs in the mitochondria (inner membrane) Uses the energy released by “falling” electrons to pump H+ across a membrane Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP Chemiosmosis Chemiosmosis is an energy coupling mechanism that uses energy stored on H+ Chemiosmosis is the coupling of the REDUX reactions of the electron transport chain to ATP synthesis – NADH passes electrons to an electron transport chain – As electrons “fall” from carrier to carrier and finally to O2 • Energy is released in small quantities NADH NAD + H + ATP 2e + Controlled release of energy for synthesis of ATP 2 H + 2e 1 2 H2O Figure 6.5C O2 ELECTRON TRANSPORT CHAIN • Electron transport systems are embedded (protein molecules) in inner mitochondrial membranes (cristae) • NADH and FADH2 give up electrons that they picked up in earlier stages to electron transport system • Electrons are transported through the system • The final electron acceptor is oxygen. The hydrogen combines with the oxygen to form water Electron transport chain H+ H+ H+ H+ + . H H+ Protein complex H+ Electron carrier Intermembrane space H+ H+ ATP synthase Inner mitochondrial membrane FADH2 Electron flow NADH FAD NAD+ + H 1 O + 2 H+ 2 2 + Mitochondrial matrix H H+ Electron Transport Chain OXIDATIVE PHOSPHORYLATION Figure 6.10 H2O ADP + P ATP H+ Chemiosmosis HOW MUCH TOTAL ATP(ENERGY) WAS PRODUCED? • Glycolysis 2 ATP formed by substrate-level phosphorylation • Krebs cycle and preparatory reactions 2 ATP formed by substrate-level phosphorylation • Electron transport phosphorylation 32-34 ATP formed 2+2+34=38 Most ATP production occurs by oxidative phosphorylation or electron transport chain WHY OXYGEN? • Electron transport phosphorylation requires the presence of oxygen • Oxygen withdraws spent electrons from the electron transport system, then combines with H+ to form water Web site tutorials to check: • http://www.sp.uconn.edu/~terry/Comm on/respiration.html • http://www2.nl.edu/jste/electron_trans port_system.htm • http://www.wisconline.com/objects/MBY2604/MBY2604.s wf An overview of cellular respiration An overview of cellular respiration Animation: Cell Respiration Overview How efficient is cellular respiration? • Only about 40% efficient. In other words, a call can harvest about 40% of the energy stored in glucose. • Most energy is released as heat Evolution of cellular respiration • When life originated, atmosphere had little oxygen • Earliest organisms used anaerobic pathways • Later, photosynthesis increased atmospheric oxygen • Cells arose that used oxygen as final acceptor in electron transport (without oxygen to act as the final hydrogen acceptor the cells will die) Fermentation • Fermentation allows some cells to produce ATP without oxygen. • This is Anaerobic respiration ANAEROBIC RESPIRATION Fermentation is an anaerobic alternative to cellular respiration • Do not use oxygen • Produce less ATP( 2) than aerobic pathways • Two types. One produces alcohol and the other lactic acid as waste products – Fermentation pathways – Anaerobic electron transport Fermentation – Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP • Begin with glycolysis • Do not break glucose down completely to carbon dioxide and water • Yield only the 2 ATP from glycolysis • Steps that follow glycolysis serve only to regenerate NAD+ Yeast • Single-celled fungi • Carry out alcoholic fermentation • Saccharomyces cerevisiae – Baker’s yeast – Carbon dioxide makes bread dough rise • Saccharomyces ellipsoideus – Used to make beer and wine Our muscle cells… • In the absence of oxygen our muscles can carry out fermentation, but the pyruvate from glycolysis is turned into lactic acid instead of alcohol – In alcohol fermentation • 2 NAD+ NADH is oxidized to NAD+ while converting pyruvate to CO2 and ethanol 2 NADH 2 NADH 2 NAD+ GLYCOLYSIS 2 ADP + 2 P Glucose 2 2 ATP 2 Pyruvate CO2 released 2 Ethanol Figure 6.13B Figure 6.13C More details… Two stages of glycolysis • Energy-requiring steps – ATP energy activates glucose and its six-carbon derivatives • Energy-releasing steps – The products of the first part are split into three-carbon pyruvate molecules – ATP and NADH form •Glycolysis harvests chemical energy by oxidizing glucose to pyruvate – In glycolysis, ATP is used to prime a glucose molecule • Which is split into two molecules of pyruvate 2 NAD+ 2 NADH + 2 H+ Glucose 2 Pyruvate 2 ADP Figure 6.7A +2 P 2 ATP – In the first phase of glycolysis • ATP is used to energize a glucose molecule, which is then split in two Steps 1 – 3 A fuel molecule is energized, using ATP. Glucose ATP PREPARATORY PHASE (energy investment) Step 1 ADP P Glucose-6-phosphate P Fructose-6-phosphate P Fructose-1,6-diphosphate 2 ATP 3 ADP P Step 4 A six-carbon intermediate splits into two three-carbon intermediates. Figure 6.7C 4 – In the second phase of glycolysis • ATP, NADH, and pyruvate are formed P Step 5 A redox reaction generates 6 9 NADH. NAD P + 5 + 5 P 6 NADH +H+ P P NADH +H+ P Steps 6 – 9 ATP and pyruvate are produced. NAD Glyceraldehyde-3-phosphate (G3P) ADP P 6 P 1,3-Diphosphoglycerate ADP 6 ATP 7 6 ATP P P 7 P 8 8 H2O 7 P 3-Phosphoglycerate 7 8 2-Phosphoglycerate 8 H2O P P 9 ADP Phosphoenolpyruvate (PEP) 9 ADP 9 ATP ENERGY PAYOFF PHASE 9 ATP Pyruvate Net Energy Yield from Glycolysis Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Glycolysis net yield is 2 ATP and 2 NADH Preparatory reactions before the Krebs cycle • Preparatory reactions – Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide – NAD+ is reduced pyruvate + coenzyme A + NAD+ acetyl-CoA + NADH + CO2 • One of the carbons from pyruvate is released in CO2 • Two carbons are attached to coenzyme A and continue on to the Krebs cycle Pyruvate is gets ready for the citric acid cycle – Prior to the citric acid cycle • Enzymes process pyruvate, releasing CO2 and producing NADH and acetyl CoA NAD+ NADH CoA 2 Pyruvate Acetyl CoA (acetyl coenzyme A) 1 Figure 6.8 + H+ CO2 3 Coenzyme A Krebs cycle – The acetyl units are oxidized to carbon dioxide – NAD+ and FAD are reduced Products: • • • • • Coenzyme A 2 CO2 3 NADH FADH2 ATP The citric acid cycle (Krebs)completes the oxidation of organic fuel (glucose), generating many NADH and FADH2 molecules – In the citric acid cycle • The two-carbon acetyl part of acetyl CoA is oxidized Acetyl CoA CoA CoA CITRIC ACID CYCLE 2 CO2 3 NAD+ FADH2 3 NADH FAD + 3 H+ ATP Figure 6.9A ADP + P Krebs Cycle or Citric Acid Cycle For each turn of the Krebs cycle • Two CO2 molecules are released (All of the carbon molecules in pyruvate end up in carbon dioxide) • Three NADH and one FADH2 (Coenzymes are reduced, they pick up electrons and hydrogen) • One molecule of ATP is formed for each turn so the net yield of ATP for the Krebs or Citric Acid cycle is 2 ATP molecules. What happened to co-enzymes (NAD and FAD) during the first two stages? Co-enzymes were reduced (gained electrons) • Glycolysis • Preparatory reactions • Krebs cycle 2 NADH 2 FADH2 + 6 NADH • Total 2 FADH2 + 10 NADH 2 NADH Most ATP production occurs by oxidative phosphorylation or electron transport chain – Electrons from NADH and FADH2 • Travel down the electron transport chain to oxygen, which picks up H+ to form water – Energy released by the redox reactions • Is used to pump H+ into the space between the mitochondrial membranes ELECTRON TRANSPORT CHAIN OR PHOSPHORYLATION • Takes place in the mitochondria • Coenzymes deliver electrons to electron transport systems • Electron transport sets up H+ ion gradients • Flow of H+ down gradients powers ATP formation • The net yield from oxidative phosphorilation is 32 to 34 ATP molecules Making ATP : Chemiosmotic model – In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes • Driving the synthesis of ATP H+ H+ H+ H+ + . H H+ Protein complex H+ Electron carrier Intermembrane space H+ H+ ATP synthase Inner mitochondrial membrane FADH2 Electron flow NADH FAD NAD+ + H 1 O + 2 H+ 2 2 + Mitochondrial matrix H H+ Electron Transport Chain OXIDATIVE PHOSPHORYLATION Figure 6.10 H2O ADP + P ATP H+ Chemiosmosis Certain poisons interrupt critical events in cellular respiration – Various poisons • • • Block the movement of electrons Block the flow of H+ through ATP synthase Allow H+ to leak through the membrane Cyanide, carbon monoxide Rotenone H+ H+ H+ Oligomycin H+ H+ H+ H+ H+ H+ ATP Synthase DNP FAD FADH2 1 O2 + 2 H+ 2 NAD+ NADH H+ H+ H2O ADP + P ATP + H Electron Transport Chain Figure 6.11 Chemiosmosis •Review: Each molecule of glucose yields many molecules of ATP – Oxidative phosphorylation, using electron transport and chemiosmosis • Produces up to 38 ATP molecules for each glucose molecule that enters cellular respiration Electron shuttle across membrane Cytoplasm Mitochondrion 2 NADH 2 NADH (or 2 FADH2) 2 NADH GLYCOLYSIS 2 Glucose Pyruvate 2 Acetyl CoA + 2 ATP by substrate-level phosphorylation CITRIC ACID CYCLE + 2 ATP by substrate-level phosphorylation Maximum per glucose: Figure 6.12 6 NADH About 38 ATP 2 FADH2 OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) + about 34 ATP by oxidative phosphorylation Anaerobic Electron Transport • Carried out by certain bacteria • Electron transport system is in bacterial plasma membrane • Final electron acceptor is compound from environment (such as nitrate), NOT oxygen • ATP yield is almost as good as from aerobic respiration INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS • Cells use many kinds of organic molecules as fuel for cellular respiration – Carbohydrates, fats, and proteins can all fuel cellular respiration • When they are converted to molecules that enter glycolysis or the citric acid cycle Food, such as peanuts Carbohydrates Fats Sugars Glycerol Proteins Fatty acids Amino acids Amino groups Glucose G3P Pyruvate Acetyl CoA GLYCOLYSIS ATP Figure 6.14 CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) How is energy obtained from proteins? • Proteins are broken down to amino acids • Amino acids are broken apart • Amino group is removed, ammonia forms, is converted to urea and excreted • Carbon backbones can enter the Krebs cycle How do we get energy from fats? • Most stored fats are triglycerides • Triglycerides are broken down to glycerol and fatty acids • Glycerol is converted to PGAL, an intermediate of glycolysis • Fatty acids are broken down and converted to acetyl-CoA, which enters Krebs cycle LE 9-19 Proteins Carbohydrates Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P NH3 Fats Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation • Food molecules provide raw materials for biosynthesis – Cells use some food molecules and intermediates from glycolysis and the citric acid cycle as raw materials – This process of biosynthesis • Consumes ATP 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 Figure 6.15 Sugars Carbohydrates • The fuel for respiration ultimately comes from photosynthesis – All organisms • Can harvest energy from organic molecules – Plants, but not animals • Can also make these molecules from inorganic sources by the process of photosynthesis Figure 6.16 Electrons “fall” from organic molecules to oxygen during cellular respiration • In cellular respiration, glucose and other fuels are oxidized, releasing energy. • In the summary equation of cellular respiration: C6H12O6 + 6O2 6CO2 + 6H2O+ ATP • Glucose is oxidized (loses electrons), oxygen is reduced ( gains electrons) • Cellular respiration does not oxidize glucose in a single step that transfers all the hydrogen in the fuel to oxygen at one time. glucose is broken down gradually in a series of steps, each catalyzed by a specific enzyme