CELLULAR RESPIRATION HARVESTING CHEMICAL ENERGY

Four Features of Enzymes 3) The same enzyme sometimes works for both the forward and reverse reactions, but not always 4) Each type of enzyme recognizes and binds to only certain substrates

Activation Energy For a reaction to occur, an energy barrier must be surmounted For a reaction to occur, an energy barrier must be surmounted Enzymes make the energy barrier smaller Enzymes make the energy barrier smaller activation energy without enzyme activation energy with enzyme energy released by the reaction products starting substance

Induced-Fit Model two substrate molecules active sight substrates contacting active site of enzyme TRANSITION STATE (tightest binding but least stable) end product enzyme unchanged by the reaction Substrate molecules are brought together Substrate molecules are brought together Substrates are oriented in ways that favor reaction Substrates are oriented in ways that favor reaction Active sites may promote acid-base reactions Active sites may promote acid-base reactions Active sites may shut out water Active sites may shut out water

Factors Influencing Enzyme Activity TemperaturepH Salt concentration Allosteric regulators Coenzymes and cofactors

Allosteric Activation allosteric activator vacant allosteric binding site active site altered, can bind substrate active site cannot bind substrate enzyme active site

Allosteric Inhibition allosteric inhibitor allosteric binding site vacant; active site can bind substrate active site altered, can’t bind substrate

Feedback Inhibition enzyme 2enzyme 3enzyme 4enzyme 5 enzyme 1 SUBSTRATE END PRODUCT (tryptophan) A cellular change, caused by a specific activity, shuts down the activity that brought it about

Effect of Temperature Small increase in temperature increases molecular collisions, reaction rates Small increase in temperature increases molecular collisions, reaction rates High temperatures disrupt bonds and destroy the shape of active site High temperatures disrupt bonds and destroy the shape of active site

Effect of pH

Enzyme Helpers Cofactors Cofactors Coenzymes Coenzymes NAD +, NADP +, FAD NAD +, NADP +, FAD Accept electrons and hydrogen ions; transfer them within cell Accept electrons and hydrogen ions; transfer them within cell Derived from vitamins Derived from vitamins Metal ions Metal ions Ferrous iron in cytochromes Ferrous iron in cytochromes

Producing the Universal Currency of Life All energy-releasing pathways All energy-releasing pathways require characteristic starting materials require characteristic starting materials yield predictable products and by- products yield predictable products and by- products produce ATP produce ATP

Photosynthesizers get energy from the sun Photosynthesizers get energy from the sun Animals get energy second- or third- hand from plants or other organisms Animals get energy second- or third- hand from plants or other organisms Regardless, the energy is converted to the chemical bond energy of ATP Regardless, the energy is converted to the chemical bond energy of ATP ATP Is Universal Energy Source

A review of how ATP drives cellular work

Making ATP Making ATP Plants make ATP during photosynthesis Plants make ATP during photosynthesis Cells of all organisms make ATP by breaking down carbohydrates, fats, and protein Cells of all organisms make ATP by breaking down carbohydrates, fats, and protein

Redox Reactions The loss of electrons is called oxidation. The loss of electrons is called oxidation. The addition of electrons is called reduction The addition of electrons is called reduction A e- + B  A + B e-

Overview of Aerobic Respiration C 6 H O 2 6CO 2 + 6H 2 0 glucose oxygen carbon water glucose oxygen carbon water dioxide dioxide

In cellular respiration, glucose and other fuel molecules are oxidized, releasing energy. In cellular respiration, glucose and other fuel molecules are oxidized, releasing energy. In the summary equation of cellular respiration: C 6 H 12 O 6 + 6O 2 -> 6CO 2 + 6H 2 O In the summary equation of cellular respiration: C 6 H 12 O 6 + 6O 2 -> 6CO 2 + 6H 2 O Glucose is oxidized, oxygen is reduced, and electrons loose potential energy. Glucose is oxidized, oxygen is reduced, and electrons loose potential energy. Cellular respiration does not oxidize glucose in a single step that transfers all the hydrogen in the fuel to oxygen at one time. Cellular respiration does not oxidize glucose in a single step that transfers all the hydrogen in the fuel to oxygen at one time. Rather, glucose and other fuels are broken down gradually in a series of steps, each catalyzed by a specific enzyme Rather, glucose and other fuels are broken down gradually in a series of steps, each catalyzed by a specific enzyme Electrons “fall” from organic molecules to oxygen during cellular respiration Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

An overview of cellular respiration (Layer 1)

An overview of cellular respiration (Layer 2)

An overview of cellular respiration (Layer 3)

Glycolysis Occurs in Two Stages Glycolysis Occurs in Two Stages Energy-requiring steps Energy-requiring steps ATP energy activates glucose and its six- carbon derivatives ATP energy activates glucose and its six- carbon derivatives Energy-releasing steps Energy-releasing steps The products of the first part are split into three-carbon pyruvate molecules The products of the first part are split into three-carbon pyruvate molecules ATP and NADH form ATP and NADH form

Energy-Requiring Steps ATP glucose glucose-6-phosphate fructose-6-phosphate fructose-1,6-bisphosphate 2 ATP invested ADP P P P

Energy- Releasing Steps ATP PGAL ATP NADH ATP 2 ATP invested NAD + PiPi PiPi 3-phosphoglycerate 2-phosphoglycerate PEP ADP 1,3-bisphosphoglycerate PPPP PP PP PP pyruvate substrate-level phosphorylation H2OH2O H2OH2O ADP

Net Energy Yield from Glycolysis Energy requiring steps: Energy requiring steps: 2 ATP invested 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Net yield is 2 ATP and 2 NADH

Occur in the mitochondria Occur in the mitochondria Pyruvate is broken down to carbon dioxide Pyruvate is broken down to carbon dioxide More ATP is formed More ATP is formed More coenzymes are reduced More coenzymes are reduced Second-Stage Reactions oxaloacetate malate citrate isocitrate  -ketogluterate fumarate succinate CoA succinyl–CoA ATP NADH FADH 2 NAD + FAD NAD + CoA H2OH2O H2OH2O H2OH2O ADP + phosphate group (from GTP) KREBS CYCLE PREPARATORY STEPS pyruvate NAD + CoA Acetyl–CoA coenzyme A (CoA) (CO 2 )

Two Parts of Second Stage Two Parts of Second Stage Preparatory reactions Preparatory reactions Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide NAD + is reduced NAD + is reduced Krebs cycle Krebs cycle The acetyl units are oxidized to carbon dioxide The acetyl units are oxidized to carbon dioxide NAD + and FAD are reduced NAD + and FAD are reduced

pyruvate + coenzyme A + NAD + acetyl-CoA + NADH + CO 2 One of the carbons from pyruvate is released in CO 2 One of the carbons from pyruvate is released in CO 2 Two carbons are attached to coenzyme A and continue on to the Krebs cycle Two carbons are attached to coenzyme A and continue on to the Krebs cycle Preparatory Reactions

What is Acetyl-CoA? A two-carbon acetyl group linked to coenzyme A A two-carbon acetyl group linked to coenzyme A CH 3 C=O Coenzyme A Acetyl group

The Krebs Cycle Overall Products Coenzyme A 2 CO 2 3 NADH FADH 2 ATP Overall Reactants Acetyl-CoA Acetyl-CoA 3 NAD + 3 NAD + FAD FAD ADP and P i ADP and P i

A summary of the Krebs cycle

Results of the Second Stage All of the carbon molecules in pyruvate end up in carbon dioxide All of the carbon molecules in pyruvate end up in carbon dioxide Coenzymes are reduced (they pick up electrons and hydrogen) Coenzymes are reduced (they pick up electrons and hydrogen) One molecule of ATP is formed One molecule of ATP is formed Four-carbon oxaloacetate is regenerated Four-carbon oxaloacetate is regenerated

Coenzyme Reductions During First Two Stages Glycolysis2 NADH Glycolysis2 NADH Preparatory Preparatory reactions 2 NADH Krebs cycle 2 FADH NADH Krebs cycle 2 FADH NADH Total 2 FADH NADH Total 2 FADH NADH

Occurs in the mitochondria Occurs in the mitochondria Coenzymes deliver electrons to electron transport systems Coenzymes deliver electrons to electron transport systems Electron transport sets up H + ion gradients Electron transport sets up H + ion gradients Flow of H + down gradients powers ATP formation Flow of H + down gradients powers ATP formation Electron Transport Phosphorylation

Electron Transport Electron Transport Electron transport systems are embedded in inner mitochondrial compartment Electron transport systems are embedded in inner mitochondrial compartment NADH and FADH 2 give up electrons that they picked up in earlier stages to electron transport system NADH and FADH 2 give up electrons that they picked up in earlier stages to electron transport system Electrons are transported through the system Electrons are transported through the system The final electron acceptor is oxygen The final electron acceptor is oxygen

Creating an H + Gradient NADH OUTER COMPARTMENT INNER COMPARTMENT

Making ATP: Chemiosmotic Model ATP ADP + P i INNER COMPARTMENT

Importance of Oxygen Electron transport phosphorylation requires the presence of 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 Oxygen withdraws spent electrons from the electron transport system, then combines with H + to form water

Summary of Energy Harvest (per molecule of glucose) Glycolysis Glycolysis 2 ATP formed by substrate-level phosphorylation 2 ATP formed by substrate-level phosphorylation Krebs cycle and preparatory reactions Krebs cycle and preparatory reactions 2 ATP formed by substrate-level phosphorylation 2 ATP formed by substrate-level phosphorylation Electron transport phosphorylation Electron transport phosphorylation 32 ATP formed 32 ATP formed

What are the sources of electrons used to generate the 32 ATP in the final stage? What are the sources of electrons used to generate the 32 ATP in the final stage? 4 ATP - generated using electrons released during glycolysis and carried by NADH 4 ATP - generated using electrons released during glycolysis and carried by NADH 28 ATP - generated using electrons formed during second-stage reactions and carried by NADH and FADH 2 28 ATP - generated using electrons formed during second-stage reactions and carried by NADH and FADH 2 Energy Harvest from Coenzyme Reductions

Energy Harvest Varies NADH formed in cytoplasm cannot enter mitochondrion NADH formed in cytoplasm cannot enter mitochondrion It delivers electrons to mitochondrial membrane It delivers electrons to mitochondrial membrane Membrane proteins shuttle electrons to NAD + or FAD inside mitochondrion Membrane proteins shuttle electrons to NAD + or FAD inside mitochondrion Electrons given to FAD yield less ATP than those given to NAD + Electrons given to FAD yield less ATP than those given to NAD +

686 kcal of energy are released 686 kcal of energy are released 7.5 kcal are conserved in each ATP 7.5 kcal are conserved in each ATP When 36 ATP form, 270 kcal (36 X 7.5) are captured in ATP When 36 ATP form, 270 kcal (36 X 7.5) are captured in ATP Efficiency is 270 / 686 X 100 = 39 percent Efficiency is 270 / 686 X 100 = 39 percent Most energy is lost as heat Most energy is lost as heat Efficiency of Aerobic Respiration

Do not use oxygen Do not use oxygen Produce less ATP than aerobic pathways Produce less ATP than aerobic pathways Two types Two types Fermentation pathways Fermentation pathways Anaerobic electron transport Anaerobic electron transport Anaerobic Pathways

Fermentation Pathways Fermentation Pathways Begin with glycolysis Begin with glycolysis Do not break glucose down completely to carbon dioxide and water Do not break glucose down completely to carbon dioxide and water Yield only the 2 ATP from glycolysis Yield only the 2 ATP from glycolysis Steps that follow glycolysis serve only to regenerate NAD + Steps that follow glycolysis serve only to regenerate NAD +

Lactate Fermentation C 6 H 12 O 6 ATP NADH 2 lactate electrons, hydrogen from NADH 2 NAD ADP 2 pyruvate 2 4 energy output energy input GLYCOLYSIS LACTATE FORMATION 2 ATP net

Alcoholic Fermentation C 6 H 12 O 6 ATP NADH 2 acetaldehyde electrons, hydrogen from NADH 2 NAD ADP 2 pyruvate 2 4 energy output energy input GLYCOLYSIS ETHANOL FORMATION 2 ATP net 2 ethanol 2 H 2 O 2 CO 2

Yeasts Single-celled fungi Single-celled fungi Carry out alcoholic fermentation Carry out alcoholic fermentation Saccharomyces cerevisiae Saccharomyces cerevisiae Baker’s yeast Baker’s yeast Carbon dioxide makes bread dough rise Carbon dioxide makes bread dough rise Saccharomyces ellipsoideus Saccharomyces ellipsoideus Used to make beer and wine Used to make beer and wine

Anaerobic Electron Transport Carried out by certain bacteria Carried out by certain bacteria Electron transport system is in bacterial plasma membrane Electron transport system is in bacterial plasma membrane Final electron acceptor is compound from environment (such as nitrate), NOT oxygen Final electron acceptor is compound from environment (such as nitrate), NOT oxygen ATP yield is almost as good as from aerobic respiration ATP yield is almost as good as from aerobic respiration

Energy from Proteins Proteins are broken down to amino acids Proteins are broken down to amino acids Amino acids are broken apart Amino acids are broken apart Amino group is removed, ammonia forms, is converted to urea and excreted Amino group is removed, ammonia forms, is converted to urea and excreted Carbon backbones can enter the Krebs cycle or its preparatory reactions Carbon backbones can enter the Krebs cycle or its preparatory reactions

Energy from Fats Most stored fats are triglycerides Most stored fats are triglycerides Triglycerides are broken down to glycerol and fatty acids Triglycerides are broken down to glycerol and fatty acids Glycerol is converted to PGAL, an intermediate of glycolysis Glycerol is converted to PGAL, an intermediate of glycolysis Fatty acids are broken down and converted to acetyl-CoA, which enters Krebs cycle Fatty acids are broken down and converted to acetyl-CoA, which enters Krebs cycle

When life originated, atmosphere had little oxygen When life originated, atmosphere had little oxygen Earliest organisms used anaerobic pathways Earliest organisms used anaerobic pathways Later, noncyclic pathway of photosynthesis increased atmospheric oxygen Later, noncyclic pathway of photosynthesis increased atmospheric oxygen Cells arose that used oxygen as final acceptor in electron transport Cells arose that used oxygen as final acceptor in electron transport Evolution of Metabolic Pathways