Cellular Respiration Cellular respiration breaks down glucose molecules and banks their energy in ATP The process uses O2 and releases CO2 and H2O Glucose Oxygen gas Carbon dioxide Water Energy Figure 6.2A

glucose GLYCOLYSIS pyruvate

Efficiency of Cellular Respiration Energy released from glucose banked in ATP Energy released from glucose (as heat and light) Gasoline energy converted to movement 100% About 40% 25% Burning glucose in an experiment “Burning” glucose in cellular respiration Burning gasoline in an auto engine Figure 6.2B

BASIC MECHANISMS OF ENERGY RELEASE Glucose gives up energy as it is oxidized Loss of hydrogen atoms Energy Glucose Gain of hydrogen atoms Figure 6.4

Hydrogen Carriers Such as NAD+ Shuttle Electrons Enzymes remove electrons from glucose molecules and transfer them to a coenzyme OXIDATION Dehydrogenase and NAD+ REDUCTION Figure 6.5

Redox reactions release energy when electrons “fall” from a hydrogen carrier to oxygen As electrons move from carrier to carrier, their energy is released in small quantities Energy released and now available for making ATP ELECTRON CARRIERS of the electron transport chain Electron flow Figure 6.6

Two Mechanisms Make ATP Cells use the energy released by “falling” electrons to pump H+ ions across a membrane The energy of the gradient is harnessed to make ATP by chemiosmosis High H+ concentration ATP synthase uses graient energy to make ATP Membrane Electron transport chain ATP synthase Energy from Low H+ concentration Figure 6.7A

Organic molecule (substrate) New organic molecule (product) ATP can also be made by transferring phosphate groups from organic molecules to ADP Enzyme Adenosine Organic molecule (substrate) This process is called substrate-level phosphorylation Adenosine New organic molecule (product) Figure 6.7B

Impacts, Issues

inner compartment outer compartment cytoplasm outer mitochondrial membrane inner mitochondrial membrane

Transfer Phosphorylation Typical Energy Yield: 36 ATP CYTOPLASM glucose ATP 2 ATP 4 Glycolysis e- + H+ (2 ATP net) 2 NADH 2 pyruvate e- + H+ 2 CO2 2 NADH e- + H+ 8 NADH 4 CO2 Krebs Cycle e- + H+ 2 ATP 2 FADH2 e- Electron Transfer Phosphorylation 32 ATP H+ water e- + oxygen Typical Energy Yield: 36 ATP

Energy-Requiring Steps of Glycolysis fructose1,6-bisphosphate 2 ATP invested Energy-Requiring Steps of Glycolysis glucose ADP P ATP glucose-6-phosphate P fructose-6-phosphate ATP fructose1,6-bisphosphate P ADP PGAL P

1,3-bisphosphoglycerate PGAL P NAD+ NADH Pi 1,3-bisphosphoglycerate P ADP ATP P 3-phosphoglycerate P 2-phosphoglycerate H2O P PEP ADP ATP pyruvate

pyruvate coenzyme A (CoA) NAD+ NADH carbon dioxide CoA acetyl-CoA PREPARATORY STEPS pyruvate coenzyme A (CoA) NAD+ NADH O O carbon dioxide CoA acetyl-CoA

An overview of cellular respiration High-energy electrons carried by NADH GLYCOLYSIS ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS KREBS CYCLE Glucose Pyruvic acid Cytoplasmic fluid Mitochondrion Figure 6.8

Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid Figure 6.9A

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

Pyruvic acid is chemically groomed for the Krebs cycle Each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle Pyruvic acid Acetyl CoA (acetyl coenzyme A) CO2 Figure 6.10

Krebs Cycle Oxidizes Organic Fuel making NADH & FADH2 Acetyl CoA The Krebs cycle is a series of reactions in which enzymes strip away electrons and H+ from each acetyl group 2 KREBS CYCLE CO2 Figure 6.11A

Alpha-ketoglutaric acid 2 carbons enter cycle Oxaloacetic acid 1 Citric acid CO2 leaves cycle 5 KREBS CYCLE 2 Malic acid 4 Alpha-ketoglutaric acid 3 CO2 leaves cycle Succinic acid Step Acetyl CoA stokes the furnace Steps and NADH, ATP, and CO2 are generated during redox reactions. Steps and Redox reactions generate FADH2 and NADH. 1 2 3 4 5 Figure 6.11B

=CoA acetyl-CoA oxaloacetate citrate CoA KREBS CYCLE NAD+ NADH isocitrate H2O H2O malate O NAD+ NADH a-ketoglutarate FAD FADH2 fumarate succinyl-CoA O CoA NAD+ NADH succinate ADP + phosphate group ATP

ELECTRON TRANSPORT CHAIN Protein complex Intermembrane space Electron carrier Inner mitochondrial membrane Electron flow Mitochondrial matrix ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.12

Electron transfer phosphorylation Bonus Electron transfer phosphorylation OUTER COMPARTMENT NADH INNER COMPARTMENT

Electron transfer phosphorylation Bonus Electron transfer phosphorylation ATP INNER COMPARTMENT ADP + Pi

Certain poisons interrupt cellular respiration Rotenone Cyanide, carbon monoxide Oligomycin ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.13

Figure 6.5 Page 87 glucose 2 ATP 2 PGAL NAD+ 4 ATP 2 ATP Krebs cycle 2 NADH 2 pyruvate 2 NADH2 2 CO2 2 acetyl-CoA 2 NADH H+ H+ 2 ATP 6 NADH Krebs cycle ATP H+ 2 FADH2 ATP H+ 4 CO2 36 ATP H+ H+ electron transfer phosphorylation ADP +Pi H+ H+ H+

Each Glucose Yields Lots of ATP For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules Cytoplasmic fluid Mitochondrion Electron shuttle across membranes KREBS CYCLE GLYCOLYSIS 2 Acetyl CoA 2 Pyruvic acid KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Glucose 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

Anaerobic Respiration: Alcohol Fermentation Pyruvic acid is converted to CO2 and ethanol This recycles NAD+ to keep glycolysis working released GLYCOLYSIS 2 Pyruvic acid 2 Ethanol Glucose Figure 6.15A Figure 6.15C

2 ATP net 2 pyruvate energy output energy input ATP NADH 2 NAD+ 2 ADP 2 pyruvate 4 energy output energy input GLYCOLYSIS ATP C6H12O6 NADH 2 NAD+ electrons, hydrogen from NADH 2 ethanol ETHANOL FORMATION 2 acetaldehyde 2 CO2 2 H2O

Anaerobic Respiration: Lactic Acid Fermentation Pyruvic acid is converted to lactic acid Lactic acid fermentation is used to make cheese and yogurt GLYCOLYSIS 2 Pyruvic acid 2 Lactic acid Glucose Figure 6.15B

ATP C6H12O6 NADH 2 NAD+ 2 2 ADP 2 pyruvate 4 energy output energy input GLYCOLYSIS 2 ATP net 2 lactate electrons, hydrogen from NADH LACTATE FORMATION

ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Pathways of molecular breakdown Food, such as peanuts Polyscaccharides Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Pyruvic acid ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Glucose G3P Acetyl CoA KREBS CYCLE GLYCOLYSIS Figure 6.16

FOOD fats glycogen complex carbohydrates proteins fatty acids glycerol simple sugars amino acids glucose-6-phosphate NH3 carbon backbones GLYCOLYSIS PGAL urea pyruvate acetyl-CoA KREBS CYCLE