Chapter 9 Cellular respiration: Harvesting Chemical energy

Figure 9.1 Energy flow and chemical recycling in ecosystems

REDOX (Reduction/Oxidation) Redox can involve loss or gain of an electron or a hydrogen (contains an electron) C6H12O6 + 6O2 ---> 6CO2 + 6H2O Carbon loses hydrogen therefore is oxidized. Oxygen gains hydrogen therefore is reduced. Reduced compounds are high energy Oxidized compounds are low energy

Figure 9.3 Methane combustion as an energy-yielding redox reaction Carbon loses electrons as oxygen is more electrophilic. Look at charge distribution. Oxidized compounds low energy, reduced are high energy

Figure 9.4 Nicotinamide Adenine Dinucleotide+ as an electron shuttle NAD+ is reduced to form NADH by gaining a hydrogen atom..and an electron to balance the charge The electron come from water therefore a proton is formed Therefore… NAD+ > NADH + H+ FAD +2H FADH2

Figure 6.8 The structure and hydrolysis of ATP  Molecule most involved in supply of energy for reactions and movements From breakdown of sugar Negative phosphates repel therefore high energy Cell and Organismal Biology 2009

Figure 6.10 The ATP cycle Cell and Organismal Biology 2009

8.11 A review of how ATP drives cellular work Roles for ATP ATP also provides phosphates and energy to phosphorylate and therefore activate or deactivate proteins

2 ways to make ATP Substrate level phosphorylation Transfer of a phosphate from an organic molecule to ADP to form ATP Phosphoenolpyruvate (PEP) Oxidative phosphorylation/electron transport system Use of NADH + H+ (reduced form) to provide energy to make ATP Requires presence of oxygen (O2)

Mitochondria

Figure 9.6 An overview of cellular respiration (Layer 3)

Glucose 6 5 1 4 2 3 C6H12O6 + 6O2 ---> 6CO2 + 6H2O

Figure 9.9 A closer look at glycolysis: energy investment phase (Layer 2) Draw carbons and phosphates at each step

Figure 9.9 A closer look at glycolysis: energy payoff phase (Layer 4)

Figure 9.8 The energy input and output of glycolysis Metabolic Energy Production Summary C6H12O6 + 6O2 6H2O + 6CO2 + energy (36 ATP) 1. Glycolysis: (Outside mitochondria in the cytoplasm) Glucose (6-carbon) is phosphorylated to Fructose 1,6-bisphosphate (2 ATP used up) F 1,6 BP split to two PGAL(G3P)(3-carbon each) Two PGAL phosphorylated to two DPGA (BPG)(2 NADH +2H+ produced) Two DPGA dephosphorylated to two pyruvate molecules (3-carbon) (4 ATP produced) Net Gain: 2 NADH + H+; 2ATP. (These two ATPs may be used up transporting the NADH + H+ to the mitochondria)

Figure 9.6 An overview of cellular respiration (Layer 3)

2. Preparation for Krebs cycle: (In mitochondria) Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the Krebs cycle (Citric Acid Cycle) 2. Preparation for Krebs cycle: (In mitochondria) CO2 removed from pyruvate as Acetyl-CoA formed (2 NADH + 2H+ produced per 2 pyruvate) Net Gain: 2 NADH + H+

Figure 9.11 A summary of the Krebs cycle

Figure 9.11 A closer look at the Krebs cycle (Layer 4) x2

3. Citric Acid Cycle (Krebs Cycle, CAC) (In mitochondria) Acetyl-CoA combines with oxaloacetic acid (4-carbon) to give 6-carbon molecule. Molecule gradually rearranged and broken down. Co-A is re-used. Oxaloacetic acid regenerated for re-use. 2 x 3 NADH + H+ produced (2 x 3 because two Acetyl-CoA enter cycle per glucose) 2 x 1 FADH2 produced 2 x 1GTP produced (later converted to ATP) 2 x 2 CO2 released So, glucose completely broken down to CO2 and high energy compounds produced Net Gain 10 NADH + H+ 2 FADH2 2 ATP (via GTP) (This is used directly in the cell)

Figure 9.6 An overview of cellular respiration (Layer 3)

Figure 9.5 An introduction to electron transport chains

Mitochondria

Figure 9.14 ATP synthase, a molecular mill So how does this gradient arise?

Figure 9.13 Free-energy change during electron transport FMN Flavin Mononucleotide FeS Iron Sulfur protein Q Ubiquinone Cyt Cytochromes 53kCal/mol energy loss from NADH to H2O

Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis

4. Chemiosmotic ATP Synthesis: (In inner mitochondrial membrane) NADH + H+ releases electrons (2e-) plus hydrogen ions (2H+) to electron transport chain. NAD+ goes back to earlier stages and is reused. Electrons pass across the membrane three times, carrying 2H+ across each time, and leaving them between the inner and outer mitochondrial membranes. So each NADH +H+ carries six hydrogen ions across. Electrons from FADH2 carry four hydrogen ions across. FAD is also re-used in CAC. So, for each glucose molecule, 68 hydrogen ions are moved across the inner mitochondrial membrane. It takes 2 hydrogen ions moving through the ATP synthase enzyme to convert ADP + Pi to ATP (34 total.) The electron pairs must now combine with half of an O2 molecule, and two H+ to give H2O. This is the source of the water in the respiration equation. Net Gain 10 NADH + H+ 2 FADH2 2 ATP (via GTP) (This is used directly in the cell)

Figure 9.16 Review: how each molecule of glucose yields many ATP molecules during cellular respiration

5. Conclusion So, 34 ATP are formed by chemisosmotic ATP synthesis. Add these to the net gain of 2 ATP from the Krebs Cycle to give a grand total of 36 ATPs formed from one molecule of glucose as it is broken down to six CO2 and 6H2O molecules. The ATP is then used elsewhere in the cell. Depending on how the cytosolic electrons are transferred to the mitochondria, yield may include the ATPs from Glycolysis (so, yield may be 38 ATP) Note that this is the theoretical yield. Actual yield is lower

Figure 9.18 Pyruvate as a key juncture in catabolism

Figure 9.17a Fermentation

Figure 9.17b Fermentation

Figure 9.20 The control of cellular respiration

Figure 9.19 The catabolism of various food molecules During beta oxidation, each acetyl group gives 4 ATPs for the break, and 12 in the Krebs cycle

Cell and Organismal Biology 2009

b-oxidation Invest ATP to prime system (-1ATP) Harvest FADH2 (2ATP) Harvest NADH (3ATP) Net gain 4ATP Plus 12 ATP from Krebs cycle