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Chapter 6 How Cells Harvest Chemical Energy How Is a Marathoner Different from a Sprinter? The different types of muscle fibers Slow- twitch (red) fibers Fast- twitch (white) fibers Slow- twitch (red) fibers Aerobic Lots of mitochondria Myglobin (carries O2- red color) Long muscle contractions Cellular respiration Fast- twitch (white) fibers Anerobic Less mitochondria Less myoglobin (pale) Quick bursts Produces less ATP Cellular respiration The aerobic harvesting of energy from sugars by cells Yields CO2, H2O and a large amount of ATP 6.1 Photosynthesis and cellular respiration provide energy for life Cellular respiration • • • • consumes O2 during the oxidation of glucose to CO2 and H2O makes ATP Photosynthesis • uses solar energy • And CO2 and H2O • To produce glucose and O2 Sunlight energy ECOSYSTEM CO2 Photosynthesis in chloroplasts Glucose + + H2O O2 Cellular respiration in mitochondria ATP (for cellular work) Heat energy 6.2 Breathing supplies oxygen to our cells and removes carbon dioxide O2 CO2 Breathing Lungs CO2 Bloodstream O2 Muscle cells carrying out Cellular Respiration Glucose + O2 CO2 + H2O + ATP 6.3 Cellular respiration banks energy in ATP molecules Cells “burn” organic molecules Through several reactions Generating 38 ATP molecules 40% efficient (car =25%) Working muscle cell requires 10 million molecules of ATP/s Where does the energy come from??? Glucose and oxygen are rearranged Bonds broken in glucose release chemical bond energy The cell stores the energy in the bonds of ATP C6H12O6 + 6 O2 Glucose Oxygen gas 6 CO2 + 6 H 2O Carbon dioxide Water + ATPs Energy 6.4 The human body uses energy from ATP for all its activities Maintenance: Blood pumping Breathing Maintain temp Digestion Energy= Kcal Average person requires 2,2000 Kcal for maintenance and voluntary actives 6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen Oxygen is very electronegative Electrons lose potential energy during their “fall” to oxygen Cellular respiration is a “controlled fall” of electrons, like stepping down a staircase Electron transfer = energy Hydrogen (1e,1p) movements = electron transfer = energy Redox Reaction (oxidation-reduction): movement of electrons from one molecule to another Oxidation- loss of electrons from one substance Reduction- addition of electrons to another substance C6H12O6 Glucose Loss of hydrogen atoms (oxidation) + 6 O2 6 CO2 Gain of hydrogen atoms (reduction) + 6 H2 O + Energy (ATP) NADH NAD+ + ATP 2e H+ 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 Controlled release of energy for synthesis of ATP 2 H+ 2 H + 2e 1 O2 2 H2O H 2O STAGES OF CELLULAR RESPIRATION AND FERMENTATION 6.6 Overview: Cellular respiration occurs in three main stages 1. Glycolysis 2. Citric Acid Cycle 3. Oxidative Phosphorylation Stage 1: Glycolysis Occurs in the cytoplasm Breaks down glucose into pyruvate producing a small amount of ATP Stage 2: The citric acid cycle Takes place in the mitochondria Completes the breakdown of glucose, producing a small amount of ATP Supplies the third stage of cellular respiration with electrons Stage 3: Oxidative phosphorylation Occurs in the mitochondria Uses the energy released by “falling” electrons to pump H+ across a membrane Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP Cellular Respiration Video NADH High-energy electrons carried by NADH NADH FADH2 and OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) CITRIC ACID CYCLE GLYCOLYSIS Glucose Pyruvate Mitochondrion Cytoplasm ATP Substrate-level phosphorylation CO2 ATP CO2 Substrate-level phosphorylation ATP Oxidative phosphorylation Stage 1: Glycolysis Occurs in the cytoplasm Breaks down glucose into pyruvate Producing a small amount of ATP Universal Anaerobic (no O2 required) Doesn’t occur in a membrane-bound organelle Ancient metabolic system 6.7 Glycolysis 1st Stage: “Splitting of Sugar” Harvests chemical energy by oxidizing glucose to pyruvate Glucose (6C) 2 Pyruvate Molecules (3C ea) Nine step process Cell reduces 2 NAD+ into 2 NADH 2 ATP via substrate level phosphorylationenzyme tranfers phosphate group from substrate molecule to ADP, forming ATP An Overview of Glycolysis 2 NAD + 2 NADH + H +2 Glucose 2 Pyruvate 2 ADP + 2 P 2 ATP Substrate-Level Phosphorylation a phosphate group is transferred (by an enzyme) from an organic molecule (substrate) to ADP Enzyme P P P Adenosine ADP P Organic molecule (substrate) ATP P The 1st Phase: 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 ADP PREPARATORY PHASE (energy investment) Step 4 A six-carbon intermediate splits into two threecarbon intermediates. Figure 6.7C P Glucose-6-phosphate P Fructose-6-phosphate P Fructose-1,6-diphosphate ATP ADP P Glyceraldehyde-3-phosphate (G3P) The 2nd Phase: ATP, NADH, and pyruvate are formed P P Step 5 A redox reaction generates NADH. 6 9 Steps 6–9 ATP and pyruvate are produced. ENERGY PAYOFF PHASE NAD+ NAD+ NADH +H P P P + 1,3 P Diphosphoglycerate NADH +H ADP 6 ATP ADP P P 6 ATP P P 3 7-Phosphoglycerate 7 P P 8 8 H2O H2O P ADP ATP 2-Phosphoglycerate P 9 ADP Phosphoenolpyruvate (PEP) 9 ATP Pyruvate What’s the payoff from Glycolyis? For each molecule of glucose: 2 NADH molecules- stored energy not available in anaerobic environment (without O2) 2 Pyruvate molecules- to be used later 4 ATP molecules BUT… The first phase uses 2 ATP molecules Net Gain= 2 ATP Molecules Not enough energy fro most organisms Yeasts, bacteria 6.8 Pyruvate is chemically groomed for the citric acid cycle Prior to the citric acid cycle Enzymes process pyruvate: 1. Carbon atom removed and released in CO2 2. Compound is oxidized and NAD+ is reduced to NADH 3. Coenzyme A joins compound Produces Acetyl Coenzyme A (acetyl CoA) A higher energy molecule for the citric acid cycle Pyruvate is chemically groomed for the citric NADH High-energy electrons acid cycle carried by NADH NADH FADH2 and NAD+ + H+ NADH OXIDATIVE PHOSPHORYLATION (Electron Transport CoA and Chemiosmosis) CITRIC ACID CYCLE GLYCOLYSIS Glucose Pyruvate Pyruvate Acetyl CoA (acetyl coenzyme A) 2 CO2 Cytoplasm Mitochondrion Coenzyme A 1 ATP Substrate-level phosphorylation CO2 3 ATP CO2 Substrate-level phosphorylation ATP Oxidative phosphorylation 6.9 STAGE 2: The citric acid cycle Takes place in the mitochondria Completes the breakdown of glucose, producing a small amount of ATP Supplies the third stage of cellular respiration with electrons Krebs Cylcle Completes the oxidation of organic fuel, generating many NADH and FADH2 molecule The two-carbon acetyl part of acetyl CoA is oxidized The Citric Acid Cycle CoA Acetyl CoA Oxaloacetate CoA 2 carbons enter cycle + H+ Citrate NADH NAD+ CO2 leaves cycle CITRIC ACID CYCLE NAD+ + NADH + H Malate ADP + P FADH2 ATP Alpha-ketoglutarate FAD CO2 leaves cycle Succinate + NADH + H Step Step 1: 1 Acetyl CoA stokes the furnace. and NAD+ Steps 2-3: Steps NADH, ATP, and CO2 are generated during redox reactions. Steps 4-5 and Steps Redox reactions generate FADH2 and NADH. What’s the payoff from The Citric Acid Cycle? Each turn of the cycle: 1 ATP molecule via substrate level phosphorylation 3 NADH 1FADH2 For each molecule of glucose (2 turns: 2 Acetyl CoA) 6 NADH 2FADH2 2 ATP So far the cell has produced: For 1 molecule of glucose: 4 ATP (substrate-level phosphorylation) 10 NADH 2 FADH2 To used the energy banked in NADH and FADH2 The cell must shuttle their electrons to the Electron Transport Chain Where energy from the oxidation of organic fuel will power the oxidative phosphorylation of ADP to ATP 6.10 Most ATP production occurs by oxidative phosphorylation 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 Creates an H+ gradient In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes Driving the synthesis of ATP Electron Transport Chain NADH NAD+ + H+ ATP 2e Controlled release of energy for synthesis of ATP H+ + H 2e H2O H 2O 1 2 O2 http://www.youtube.com/watch?v=9UM78eqy1oc H+ Protein complex H+ H+ H+ + H . H+ H+ Electron carrier ATP H+ synthase + H Intermembrane space Inner mitochondrial membrane Electron flow Mitochondrial matrix FADH2 FAD NAD+ NADH H+ 1 O + 2H+ 2 2 H+ + + H H2O ADP Electron Transport Chain OXIDATIVE PHOSPHORYLATION P + ATP H Chemiosmosis 6.12 : Each molecule of glucose yields many molecules of ATP: Oxidative phosphorylation, using electron transport and chemiosmosis Electron shuttle across membrane Mitochondrion 2 NADH 2 NADH 6 NADH 2 FADH2 2 NADH GLYCOLYSIS Glucose 2 Pyruvate + 2 ATP by substrate-level phosphorylation Cytoplasm (or 2 FADH2) CITRIC ACID CYCLE 2 Acetyl CoA + 2 ATP by substrate-level phosphorylation Maximum per glucose: About 38 ATP OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) + about 34 ATP by oxidative phosphorylation 6.13 Fermentation is an anaerobic alternative to cellular respiration Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP 2 ATP per glucose Lactic Acid Fermentation Alcohol Fermentation INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS 6.14 Cells use many kinds of organic molecules as fuel for cellular respiration Food, such as peanuts Fats Carbohydrates Sugars Proteins Glycerol 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 Acetyl CoA GLUCOSE SYNTHESIS Glucose Pyruvate G3P Amino groups Amino acids Proteins Fatty acids Glycerol Fats Cells, tissues, organisms Sugars Carbohydrates 6.16 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