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Biology 20 Chapter 5 Cellular Respiration McGraw - Hill Ryerson pgs. 182 - 199 Cellular Respiration A process cells use to release energy needed for all kinds of work Example: Muscular contraction 2 types of cellular respiration: 1. 2. Aerobic respiration (O2 required) Anaerobic respiration (O2 not required) The Importance of Cellular Respiration Recall: Photosynthesis converts light E into chemical E Glucose can be: Used immediately Stored for a medium – term Used to synthesize molecules that can store E for long term • Plants: glucose starch • Animal and fungal cells: glucose glycogen The Importance of Cellular Respiration glucose + oxygen carbon dioxide + water + energy C6H12O6(s) + 6 O2 6 CO2(g) + 6 H2O(l) + energy Glucose is converted into energy molecule, ATP (adenosine triphosphate) Intermediate products include: NADH, FADH2, ATP •Intermediate products NADH is reduced form of NAD+ (nicotinamide adenine dinucleotide) FADH2 is reduced form of FAD+ (flavin adenine dinucleotide) Electron carriers Transfer e- through oxidation – reduction reactions LEO, GER •Transfer of e Releases E Produces more stable ions or compounds Products have less E than reactants Thus, E is released during oxidation Can be used to make ATP e – transport chains (ETC) Shuttle e – from one molecule to another High energy ATP formation reactants oxidation - energy reduction reaction from reaction products Low energy ADP + Pi ATP I.) Energy, Cells, and ATP 1 human cell contains about 1 billion ATP molecules Active transport Movement of substances through a membrane against a concentration gradient Requires a membrane – bound carrier protein and ATP •Active transport Carrier proteins are “pumps” Ex: sodium – potassium pump Without pump, nerve and muscle cells could not function Other pumps move: Vitamins, amino acids, and H+ •ATP Another use is large – scale motion Muscular contraction Requires movement of 2 different protein molecules sliding past one another ATP supplies E to change shape of one of the molecules • Result: movement of contractile fibers Uses of ATP Functions Role of ATP requiring ATP Examples Motion Chromosomes movements during cell division Movement of organelles such as contractile vacuoles emptying Cytoplasmic streaming Formation of pseudopods in lymphocytes (WBCs) or amoebas Beating of cilia or flagella such as in sperm cells or in unicellular organisms Various specialized fibers within cells contract causing movement of or within cell Uses of ATP Functions Role of ATP requiring ATP Examples Motion Causes muscle fibers to contract Transport of ions and molecules Powers active transport of molecules against concentration gradient across membrane Contraction of skeletal, smooth, and cardiac muscles Sodium – potassium pump H+ ion pump Uses of ATP Functions Role of ATP requiring ATP Building molecules Switching reactions on or off Examples Provides E Joining amino acids needed to build any in protein synthesis large molecule Building new strands of DNA during DNA replication Alters shape of Switches certain molecules, which enzymes on or off alters function of molecules Uses of ATP Functions requiring ATP Role of ATP Examples bioluminescence Reacts with a Produces light in molecule called some light – generating luciferin and species oxygen oExample: glow worms and fireflies II.) Glucose and ATP Glucose is our “blood sugar” High E content Small Highly soluble Thus, ideal for transportation within and between cells, and throughout body III.) Releasing Energy During respiration: Chemical bonds of reactant food molecules are broken New bonds are formed in resulting chemical products E is required to break bonds E is released when new bonds form Respiration is an E releasing process because: More E is released during formation of product molecules than is consumed to break apart reactant molecules •Cellular respiration is not 100 % efficient 36 % of E content of 1 glucose molecule is converted into ATP Thus, 64 % is released as heat Used to maintain body temperature in birds and mammals Cell is quite efficient compared to automobiles (25 – 30 % efficient) Cell resp 1. Aerobic Cellular Respiration Occurs in presence of O2 (g) and involves complete oxidation of glucose Involves 4 stages 1. Glycolysis 2. Pyruvate oxidation. 3. Krebs cycle 4. Electron transport chain and chemiosmosis. Overall aerobic respiration equation: C6H12O6(s) + 6 O2 + 36 ADP + 36 Pi 6 CO2(g) + 6 H2O(l) + 36 ATP 2. Anaerobic cellular respiration Occurs in absence of O2 (g) and glucose is not completely oxidized 2 types of anaerobic cellular respiration Both types have two stages that occur in cytoplasm of cells Stage 1: glycolysis Stage 2: fermentation Anaerobic respiration Anerobic cellular respiration type 1 C6H12O6(s) + 2 ADP + 2 Pi 2 C2H5OH (l) + 2 CO2 (g) + 2 ATP ethanol Anerobic cellular respiration type 2 C6H12O6(s) + 2 ADP + 2 Pi 2 C3H6O3 (l) + 2 ATP lactic acid Stage 1- Glycolysis Aerobic respiration produces more ATP molecules than either type of anaerobic cellular respiration. Glycolysis: Occurs in both aerobic and anaerobic cellular respiration Occurs in cytoplasm of all cells An anaerobic process 10 reactions, each is catalyzed by enzyme 2 ATP molecules are used, 4 ATP molecules and 2 NADH+ ions produced Converts a 6-Carbon glucose to 2 3-C pyruvate molecules. 2 2 2 2 H2O 2 Reactants and products of glycolysis Reactants Products Glucose 2 pyruvate (2 C3H4O3) 2 NAD+ 2 NADH 2 ATP 2 ADP 4 ADP 4 ATP *note: net 2 ATP since 2 ATP are required to replenish the 2 used in step 1 of glycolysis 1 glucose + 2 ADP + 2 Pi + 2 NAD+ 2 pyruvate + 2 ATP + 2 NADH + 2 H+ •Glycolysis is not efficient Transfers 2.2 % of available energy in glucose to ATP Some is released as heat Most E remains in 2 pyruvate and 2 NADH Some unicellular microorganisms use glycolysis for their E needs Aerobic Cellular Respiration End products are: CO2 (g) , H2O (l) , ATP Uses mitochondria: Eukaryotic organelle in cell cytoplasm Specialize in production of ATP Consists of double membrane: Smooth outer membrane Semi - permeable Highly folded inner membrane Associated with cellular respiration Inner membrane- Creates 2 compartments within mitochondria Mitochondrial matrix Protein – rich liquid that fills innermost space of mitochondria Fluid – filled intermembrane space Lies between inner and outer membrane Stage 2: Pyruvate Oxidation Connects glycolysis in cytoplasm with Krebs cycle in mitochondrial matrix. 2 pyruvate molecules are transported through 2 outer mitochondrial membranes into matrix. 3 steps: Carbon dioxide removed. Acetic acid forms Co-enzyme A attaches to acetic acid = acetyl co-A. Steps Step 1: CO2 is removed from each pyruvate Pyruvate is decarboxylated 1/3 of CO2 breathed out as a waste product Step 2: Acetic Acid forms Remaining 2 carbon portions are oxidized by NAD+. Each NAD+ gains 2 H+ ions (2 protons and 2 electrons) from pyruvate 2 NADH proceed to stage 4 of aerobic respiration Remaining 2 C compound becomes acetic acid (acetyl group) Step 3: Acetyl co-A forms. Coenzyme A (CoA) becomes attached to acetic acid group Forms 2 acetyl CoA Enters next stage of aerobic cellular respiration Stage 3: The Krebs Cycle Occurs 2 times for every glucose molecule. Cyclic because one of the products of step 8 becomes a reactant in step 1. Begins when acetyl – CoA (2 per glucose) condenses with oxaloacetate to form citric acid. In 1 turn of the cycle, the 2 C atoms that were originally in glucose are removed as CO2. Pyruvate is oxidized, NAD+ and FAD are reduced. Free E is transferred to ATP, NADH, and FADH2 The process. 1. 2. 3. 4. 5. 2 carbons enter (as Acetyl co-A). 2 carbons leave as carbon dioxide- released as waste. (3) NAD+ are reduced to form NADH. (1) FAD is reduced to form FADH2. 1 ATP is produced. * Remember this happens 2 times for every glucose! Stage 4: Electron Transport and Chemiosmosis 2 Parts: ETC and Chemiosmosis. NADH and FADH2 eventually transfer H atom electrons to a a series of protein compounds Associated with inner mitochrondrial membrane called electron transport chain (ETC). Part I: Electron Transport Chain Process 1. 1 NADH gives up 2 e- at beginning of ETC H+ ion is also released into matrix 2. e- shuttles through ETC As e – move from carrier to carrier, they release E E is used to force H+ from within matrix across inner membrane 3. Each H+ ion gains potential E, as they move through protein pumps into intermembrane space 4. e – reach last components of ETC and now have low E E used to pump H+ ions 5. O2 (g) strips 2 e- from final energy carrier With 2 H+ ions, forms H2O (l) 6. Both NADH and FADH2 deliver e – to ETC -Differences between NADH and FADH2 FADH2 has a lower E content Thus, E released is not sufficient to pump as many H+ ions FADH2 enters ETC at a different location ETC mechanism Converts chemical E, in e-, into electrochemical potential H+ ion gradient across inner mitochondrial membrane Analogy: stored E possessed by a charged battery Part 2: Chemiosmosis and Oxidative ATP Synthesis 1. H+ ions accumulate in intermembrane space create an electrochemical gradient that stores E 2. Higher positive charge in intermembrane space than in matrix Creates a potential difference (voltage) across inner mitochondrial membrane 3. Inner mitochondrial membrane is impermeable to H+ ions H+ ions move through proton channels associated with ATP synthase (ATPase) enzyme As H+ ions move through ATPase complex, E that is released drives the synthesis of ATP from ADP and Pi in matrix Energy needs 1 NADH pumps enough H+ ions to generate 3 ATPs 1 FADH2 pumps enough H+ ions to generate 2 ATPs •Review: ETC followed by chemiosmosis is last stage of oxidative phosphorylation. Began with reduction of NAD+ and FAD with H atoms from glucose Continual production of ATP is dependent on maintenance of H+ reservoir Depends on continual movement of e- through ETC Dependent on availability of oxygen as final e - acceptor Review: e- are pulled down ETC E released keeps H+ ions moving into H+ reservoir Fall back into matrix Drive synthesis of ATP • Oxidative ATP synthesis Final step: ATP is transported through both mitochondrial membranes into cytoplasm Energy tally Step NADH FADH2 ATP Glycolysis 2 0 2 Pyruvate oxidation 2 0 0 Krebs cycle 6 2 2 ETC/Chemiosmosis 0 0 32 Total = 36 ATP Aerobic Respiration Energy Balance Sheet # of ATP varies according to type of cell and various environmental conditions Theoretical yield: 36 ATP per glucose per cell Actual yield: 30 ATP per glucose per cell Glycolysis is only 2.2 % efficient However, aerobic respiration is 32 % efficient Still, very good! Links Electron Transport and ATP Synthesis http://bcs.whfreeman.com/thelifewire/content/chp 07/0702001.html http://highered.mcgrawhill.com/olc/dl/120071/bio11.swf Anaerobic Cellular Respiration Glycolysis is 1st step Conversion of NAD+ to NADH is crucial, otherwise, glycolysis will halt Anaerobic organisms transfer H atoms from NADH to organic molecules instead of ETC, used by aerobic organisms Fermentation •Fermentation 2 types: Alcohol fermentation- plants. Lactic acid fermentation- animals. Similarities: Both occur in 2 stages Both occur in cytoplasm of cell Both require glycolysis as 1st step I.) Alcohol Fermentation NADHs produced during glycolysis pass H atoms to acetaldehyde 2 Acetaldehyde forms when 2 CO2 is removed from 2 pyruvate Enzyme pyruvate decarboxylase is used 2 Ethanol is produced Process recycles NAD+ and allows glycolysis to continue C6H12O6(s) + 2 ADP + 2 Pi 2 C2H5OH (l) + 2 CO2 (g) + 2 ATP ethanol •Applications of Alcohol Fermentation Carried out by yeast cells Breads, pastries, wine, beer, liquor, soy sauce Bread Leavened by mixing yeast cells with flour and H2O Yeast cells ferment glucose in starch Release CO2 Cause bread to rise •Beer and wine making Yeast cells ferment sugars found in fruit juices Mixture bubbles as yeast cells release CO2 and ethanol Wine making Fermentation ends when concentration of ethanol is 12 % Yeast cells die due to alcohol accumulation Food products dependent on microbial fermentation Food Raw material Bread Flour Soy sauce Soya bean Vinegar Alcohol (from fruit or grain fermentation) Chocolate Cacao bean Sauerkraut Cabbage Wine and beer Grapes and barley •Louis Pasteur Provided experimental evidence that yeast was responsible for alcohol fermentation Further work led him to discover that many diseases were caused by microbes II.) Lactic Acid Fermentation Under normal conditions, animals obtain E from glucose by aerobic respiration Strenuous exercise: Muscle cells demand more ATP than can be supplied by aerobic respiration alone Additional ATP supplied by lactic acid fermentation •Lactic Acid Fermentation Process NADH produced during glycolysis transfers H atoms to pyruvate in cytoplasm Regenerates NAD+ Allows glycolysis to continue Pyruvate lactic acid C6H12O6(s) + 2 ADP + 2 Pi 2 C3H6O3 (l) + 2 ATP lactic acid •Accumulation of lactic acid consequences Causes muscle stiffness, soreness, and fatigue Lactic acid is transported from muscles to liver When vigorous exercise ceases: Lactic acid is converted back to pyruvate Enters remaining stages of aerobic respiration Extra O2 is required to chemically process lactic acid “Oxygen debt” - panting Exercise Physiology: VO2 max and Lactic Acid Threshold Exercise physiology Branch of biology dealing with body’s biological responses Most common question: shortage of energy by athletes Athletic fitness Measure of ability of heart, lungs, and bloodstream to supply O2 to cells of body Other factors to athletic fitness: Muscular strength, muscular endurance, flexibility, body composition (ratio of fat to bone to muscle) Maximum oxygen consumption (VO2 max) A measure of body’s capacity to generate E required for physical activity Treadmill exercise test is used to measure VO2 max 10 – 15 minute test Animal is forced to move faster and faster on a treadmill Expired air is collected and measured by a computer VO2 max measures: Volume of O2 (mL) that cells of body can remove from bloodstream in 1 minute per kg of body mass While body experiences maximum exertion Values VO2 max values: Average: 35 mL/kg/min. Athletes: 70 mL/kg/min. VO2 max Can be increased with more exercise Genetic variation is also a factor Decreases with age Lactic acid threshold Value of exercise intensity at which blood lactic acid concentration begins to increase sharply Exercising beyond threshold may limit duration of exercise Due to pain, muscle stiffness, and fatigue Athletic training improves blood circulation and efficiency of O2 delivery to body cells Result: Decrease in lactic acid production Increase in lactic acid threshold Untrained individuals reach a lactic acid threshold at 60 % VO2 max Elite athletes reach threshold at or above 80 % VO2 max Supplements and toxins Creatine phosphate May serve as an E source by donating its phosphate to ADP Occurs naturally in body and many foods Athletes consume compound to produce more ATP in muscles Compound may also buffer muscle cells and delay onset of lactic acid fermentation Potential harmful side – effects are possible Chemical toxicity Cyanide and hydrogen sulfide directly act on specific reactions within respiration pathway Carbon Monoxide Poisoning: CO competes for protein binding sites on RBC Hemoglobin proteins carry O2 throughout body Severe drop in blood’s oxygen carrying capacity Possible death by asphyxiation Without O2, immediate halt to ETC and pumping of H+ ions across inner mitochondrial membrane • Cell death