Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cellular respiration oxidizes sugar and produces ATP in three main stages –Glycolysis occurs in the cytoplasm –The Krebs cycle and the electron transport chain occur in the mitochondria Overview: Respiration occurs in three main stages STAGES OF CELLULAR RESPIRATION AND FERMENTATION

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An overview of cellular respiration Figure 6.8 High-energy electrons carried by NADH GLYCOLYSIS GlucosePyruvic acid KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion Cytoplasmic fluid

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid Figure 6.9A GlucosePyruvic acid

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Details of glycolysis Figure 6.9B Steps – A fuel molecule is energized, using ATP Glucose PREPARATORY PHASE (energy investment) Step Glucose-6-phosphate Fructose-6-phosphate Glyceraldehyde-3-phosphate (G3P) Step A six-carbon intermediate splits into two three-carbon intermediates. 4 Step A redox reaction generates NADH. 5 5 ENERGY PAYOFF PHASE 1,3-Diphosphoglyceric acid (2 molecules) 6 Steps – ATP and pyruvic acid are produced Phosphoglyceric acid (2 molecules) 7 2-Phosphoglyceric acid (2 molecules) 8 9 (2 molecules per glucose molecule) Pyruvic acid Fructose-1,6-diphosphate

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Each pyruvic acid molecule is broken down to form CO 2 and a two-carbon acetyl group, which enters the Krebs cycle Pyruvic acid is chemically groomed for the Krebs cycle Figure 6.10 Pyruvic acid CO 2 Acetyl CoA (acetyl coenzyme A)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Krebs cycle is a series of reactions in which enzymes strip away electrons and H + from each acetyl group The Krebs cycle completes the oxidation of organic fuel, generating many NADH and FADH 2 molecules Figure 6.11A Acetyl CoA KREBS CYCLE 2 CO 2

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6.11B Oxaloacetic acid Step Acetyl CoA stokes the furnace 1 2 carbons enter cycle Citric acid Steps and NADH, ATP, and CO 2 are generated during redox reactions. 23 CO 2 leaves cycle Alpha-ketoglutaric acid CO 2 leaves cycle Succinic acid KREBS CYCLE Steps and Redox reactions generate FADH 2 and NADH. 45 Malic acid

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The electrons from NADH and FADH 2 travel down the electron transport chain to oxygen Energy released by the electrons is used to pump H + into the space between the mitochondrial membranes In chemiosmosis, the H + ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP Chemiosmosis powers most ATP production

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis in the mitochondrion Figure 6.12 Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Protein complex Electron carrier Electron flow ELECTRON TRANSPORT CHAIN ATP SYNTHASE

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Connection: Certain poisons interrupt critical events in cellular respiration Figure 6.13 Rotenone Cyanide, carbon monoxide Oligomycin ELECTRON TRANSPORT CHAIN ATP SYNTHASE

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules Review: Each molecule of glucose yields many molecules of ATP KREBS CYCLE Electron shuttle across membranes Cytoplasmic fluid GLYCOLYSIS Glucose 2 Pyruvic acid 2 Acetyl CoA KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion by substrate-level phosphorylation used for shuttling electrons from NADH made in glycolysis by substrate-level phosphorylation by chemiosmotic phosphorylation Maximum per glucose: Figure 6.14

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP –But a cell must have a way of replenishing NAD+ Fermentation is an anaerobic alternative to aerobic respiration

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In alcoholic fermentation, pyruvic acid is converted to CO 2 and ethanol Figure 6.15A –This recycles NAD + to keep glycolysis working GLYCOLYSIS 2 Pyruvic acid released 2 Ethanol Glucose Figure 6.15C

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In lactic acid fermentation, pyruvic acid is converted to lactic acid –As in alcoholic fermentation, NAD + is recycled Lactic acid fermentation is used to make cheese and yogurt GLYCOLYSIS 2 Pyruvic acid 2 Lactic acid Glucose Figure 6.15B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Polysaccharides can be hydrolyzed to monosaccharides and then converted to glucose for glycolysis Proteins can be digested to amino acids, which are chemically altered and then used in the Krebs cycle Fats are broken up and fed into glycolysis and the Krebs cycle Cells use many kinds of organic molecules as fuel for cellular respiration INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Pathways of molecular breakdown Figure 6.16 Food, such as peanuts PolysaccharidesFatsProteins SugarsGlycerolFatty acidsAmino acids Amino groups GlucoseG3P Pyruvic acid GLYCOLYSIS Acetyl CoA KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In addition to energy, cells need raw materials for growth and repair –Some are obtained directly from food –Others are made from intermediates in glycolysis and the Krebs cycle Biosynthesis consumes ATP Food molecules provide raw materials for biosynthesis

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Biosynthesis of macromolecules from intermediates in cellular respiration Figure 6.17 ATP needed to drive biosynthesis PolyscaccharidesFatsProteins KREBS CYCLE Acetyl CoA Pyruvic acid G3PGlucose GLUCOSE SYNTHESIS Amino groups Amino acidsFatty acidsGlycerolSugars Cells, tissues, organisms

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings All organisms have the ability to harvest energy from organic molecules –Plants, but not animals, can also make these molecules from inorganic sources by the process of photosynthesis The fuel for respiration ultimately comes from photosynthesis Figure 6.18