 Bioenergetics – our cells’ ability to release the energy in glucose, starch, and fat  We do this by chemical reactions catalyzed by enzymes  Exergonic reactions vs. endergonic reactions  Exergonic – nutrients being oxidized in the mitochondria  Endergonic – plants using CO 2 and water to form sugars  Activation energy – energy barrier that must be broken for exergonic rxns to proceed.

(a) Exergonic reaction: energy released, spontaneous (b) Endergonic reaction: energy required, nonspontaneous Reactants Energy Products Progress of the reaction Amount of energy released (  G  0) Reactants Energy Products Amount of energy required (  G  0) Progress of the reaction Free energy

Figure 8.8b Adenosine triphosphate (ATP) Energy Inorganic phosphate Adenosine diphosphate (ADP) (b) The hydrolysis of ATP

How the Hydrolysis of ATP Performs Work The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction Overall, the coupled reactions are exergonic Obeys the laws of thermodynamics, but less messy © 2011 Pearson Education, Inc.

Figure 8.9 Glutamic acid Ammonia Glutamine (b) Conversion reaction coupled with ATP hydrolysis Glutamic acid conversion to glutamine (a) (c) Free-energy change for coupled reaction Glutamic acid Glutamine Phosphorylated intermediate Glu NH 3 NH 2 Glu  G Glu = +3.4 kcal/mol ATP ADP NH 3 Glu P P i ADP Glu NH 2  G Glu = +3.4 kcal/mol Glu NH 3 NH 2 ATP  G ATP =  7.3 kcal/mol  G Glu = +3.4 kcal/mol +  G ATP =  7.3 kcal/mol Net  G =  3.9 kcal/mol 1 2

 Lower activation energy  Specificity  Active site binds substrate in lock and key fit – enzyme/substrate complex  Induced fit – when enzyme changes its shape to accommodate substrate  Enzymes are not used up in the reaction  Do not work alone – need co-enzymes like vitamins, NAD, and NADP

Figure 8.13 Course of reaction without enzyme E A without enzyme E A with enzyme is lower Course of reaction with enzyme Reactants Products  G is unaffected by enzyme Progress of the reaction Free energy

Figure 8.14 Substrate Active site Enzyme Enzyme-substrate complex (a) (b)

Figure Substrates Substrates enter active site. Enzyme-substrate complex Enzyme Products Substrates are held in active site by weak interactions. Active site can lower E A and speed up a reaction. Active site is available for two new substrate molecules. Products are released. Substrates are converted to products

1. Temperature  Increasing temp. increasing rxn rate  Too much heat can damage the enzyme – denature  most human enzymes work at 37 degrees Celsius 2. pH 3. Enzyme concentration 4. Substrate concentration

Figure 8.16 Optimal temperature for typical human enzyme (37°C) Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria (77°C) Temperature (°C) (a) Optimal temperature for two enzymes Rate of reaction pH (b) Optimal pH for two enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme)

 Allosteric regions on an enzyme can be bound by inhibitors or activators  Allosteric sites are subject to feedback inhibition – where the product inhibits the rxn.  Competitive inhibition – when the allosteric inhibitor binds the active site of the enzyme  Non-competitive inhibition – when the inhibitor binds another site on the enzyme leading to a conformational change in the active site

Figure 8.17 (a) Normal binding(b) Competitive inhibition (c) Noncompetitive inhibition Substrate Active site Enzyme Competitive inhibitor Noncompetitive inhibitor

Figure 8.19 Regulatory site (one of four) (a) Allosteric activators and inhibitors Allosteric enzyme with four subunits Active site (one of four) Active form Activator Stabilized active form Oscillation Non- functional active site Inactive form Inhibitor Stabilized inactive form Inactive form Substrate Stabilized active form (b) Cooperativity: another type of allosteric activation

Figure 8.21 Active site available Isoleucine used up by cell Feedback inhibition Active site of enzyme 1 is no longer able to catalyze the conversion of threonine to intermediate A; pathway is switched off. Isoleucine binds to allosteric site. Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Intermediate A Intermediate B Intermediate C Intermediate D Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 End product (isoleucine)

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 Photosynthesis  Cellular respiration

Figure Electrons carried via NADH Electrons carried via NADH and FADH 2 Citric acid cycle Pyruvate oxidation Acetyl CoA Glycolysis Glucose Pyruvate Oxidative phosphorylation: electron transport and chemiosmosis CYTOSOL MITOCHONDRION ATP Substrate-level phosphorylation Oxidative phosphorylation

Figure 9.8 Energy Investment Phase Glucose 2 ADP  2 P 4 ADP  4 P Energy Payoff Phase 2 NAD +  4 e   4 H + 2 Pyruvate  2 H 2 O 2 ATP used 4 ATP formed 2 NADH  2 H + Net Glucose 2 Pyruvate  2 H 2 O 2 ATP 2 NADH  2 H + 2 NAD +  4 e   4 H + 4 ATP formed  2 ATP used

Figure 9.10 Pyruvate Transport protein CYTOSOL MITOCHONDRION CO 2 Coenzyme A NAD  + H  NADH Acetyl CoA 123

Figure NADH 1 Acetyl CoA Citrate Isocitrate  -Ketoglutarate Succinyl CoA Succinate Fumarate Malate Citric acid cycle NAD  NADH FADH 2 ATP + H  NAD  H2OH2O H2OH2O ADP GTPGDP P i FAD CoA-SH CO2CO2 CO2CO2 Oxaloacetate

Figure 9.15 Protein complex of electron carriers (carrying electrons from food) Electron transport chain Oxidative phosphorylation Chemiosmosis ATP synth- ase I II III IV Q Cyt c FAD FADH 2 NADH ADP  P i NAD  HH 2 H  + 1 / 2 O 2 HH HH HH 21 HH H2OH2O ATP

Figure ADP 2 ATP Glucose Glycolysis 2 Pyruvate 2 CO 2 2  2 NADH 2 Ethanol 2 Acetaldehyde (a) Alcohol fermentation (b) Lactic acid fermentation 2 Lactate 2 Pyruvate 2 NADH Glucose Glycolysis 2 ATP 2 ADP  2 P i NAD 2 H   2 P i 2 NAD    2 H 

Animations Glycolysis Krebs cycle Oxidative phosphorylation