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Bio 100 Chapter 7
- 1. Chapter 7 Pathways of Cellular Respiration
- 2. Glucose breakdown releases energy Cellular respiration is a redox reaction that requires C 6H12O6 and O2 • Oxidation – Removal of H+ • Reduction – Addition of H+ • Glucose is oxidized to CO2 • Oxygen is reduced to H2O • Oxidation of glucose to CO2 releases energy, which is then used for ATP production
- 3. • NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) are coenzmes that aid in glucose oxidation • (NAD+) + (2e-) + (H+) NADH • (FAD) + (2e-) + (2H+) FADH2 • The high energy electrons in NADH and FADH2 are taken to the electron transport chain within a mitochondrion • O2 picks up electrons at the end of the chain, then takes on H+ to become H2O • NAD+ and FAD return to pick up more electrons
- 4. Cellular respiration involves the cytoplasm and mitochondria 4 stages of cellular respiration • Glycolysis – In cytoplasm – No oxygen required (anaerobic) • Preparatory reaction – In mitochondria matrix – Requires oxygen (aerobic) • Krebs cycle – In mitochondria matrix – Requires oxygen (aerobic) • Electron transport chain (ETC) – In mitochondria cristae – Requires oxygen (aerobic) A: intermembrane space In aerobic phases, oxygen is the final acceptor of electrons B: matrix C: cristae
- 5. Oxidation of glucose • Glycolysis – Glucose is broken into 2 molecules of pyruvate – NADH produced – Net 2 ATP produced • Preparatory reaction – Pyruvate oxidized (loses H+) releasing CO2 – NADH produced – End product – 2, 2 carbon acetyle groups • Krebs cycle (citric acid cycle) – Oxidation of glucose products – NADH and FADH2 result – CO2 released – 2 ATP produced per glucose molecule
- 6. Production of most ATP • Electron transport chain – NADH and FADH2 bring high energy electrons – As electrons go down chain, energy is released and captured – O2 accepts electrons at the end of the chain, which then combines with H+ to form H2O
- 7. The chemical energy of glucose becomes the chemical energy of ATP Glycolysis: Glucose breakdown begins • Occurs in cytoplasm • No oxygen required Energy investment steps • 2 ATP breaks glucose into 2 G3P molecules
- 8. Energy harvesting steps • G3P oxidized (H+ removed) • H+ combines with NAD+ to create NADH – 2 high energy electrons on NADH • P attaches to the oxidized G3P • P is added to ADP to create ATP • ATP synthesis occurs again • 2 pyruvate and 2 ATP are final products
- 10. The preparatory reaction occurs before the Krebs cycle • The preparatory reactions – In mitochondria matrix – Pyruvate is oxidized (H+ removed) creating an acetyl group – H+ taken up by NAD+ to form NADH – Acetyl group combines with CoA and goes to the Krebs cycle – NADH goes to electron transport chain – CO2 leaves the body
- 11. The Krebs cycle generates much NADH • In matrix • Acetyle group removed from CoA • Acetyl group joins a 4-carbon group to create citrate • Citrate oxidized (H+ removed) – NADH created – CO2 created • 2 ATP formed • FAD oxidized to form FADH2 • 4 CO2, 6 NADH, 2 FADH2, and 2 ATP are final products • FADH2 and NADH goes to electron transport chains
- 13. The electron transport chain captures energy for ATP production • In mitochondria cristae • NADH and FADH2 release electrons and H+ – Electrons energy electron transport chain – NAD+ and FAD result • Electrons release energy as they go down chain, which is used to make ATP • Electrons combine with O2 and H+ to form H2O • 3 ATP produced per NADH (30 ATP total) • 2 ATP produced per FADH2 (4 ATP total)
- 14. The ATP synthase complex produces ATP • Hydrogen pumped to intermembrane space from NADH and FADH2 creating a concentration gradient • Hydrogen then moves down the gradient into matrix via H+ channel protein • ATP synthase enzyme is attached to H+ channel protein and produces ATP as H+ passes through protein • ATP leaves mitochondria to go to where it is needed
- 15. The ATP payoff can be calculated • In the cytoplasm – Glycolysis • 2 ATP • In the mitochondria – Preparatory reaction • No ATP produced – Krebs cycle • 2 ATP – Electron transport chain • 32 or 34 ATP • 3 ATP per NADH • 2 ATP per FADH2 • In many animals NADH formed in glycolysis cannot cross inner mitochondrial membrane so 1 ATP per NADH is used to move them across Glucose breakdown results in 36 or 38 ATP 39% of available energy in glucose is transferred to ATP, the rest of the energy is lost as heat
- 17. Fermentation is inefficient When oxygen is in short supply, the cell switches to fermentation • 2 ATP produced per glucose molecule • In animals: pyruvate accepts electrons and is reduced to lactate • In other organisms: alcohol and CO2 are produces
- 18. • Benefits versus drawbacks of fermentation – Can occur without oxygen – Provide quick bursts of energy (important for muscle cells) – Products are toxic to cells • Yeast produces alcohol, but it kills them (wine) • Lactate builds up in muscle cells, which changes the cell pH and causes the “burn” – The liver can convert lactate back to pyruvate so cellular respiration can produce the remaining ATP
- 19. Metabolic pathways cross at particular substrates Organic molecules can be broken down and synthesized as needed • Catabolism – breaking down of molecules – Fats are a glycerol (can enter glycolysis) and 3 fatty acids (can convert to acetyl CoA and energy the Krebs cycle) – Carbon skeleton of amino acids can enter glycolysis, be converted to acetyle CoA, or enter the Krebs cycle directly • Anabolism – building up of molecules – G3P from glycolysis can be converted to glycerol, acetyl groups from the preparatory reactions can be joined to form fatty acids, fat synthesis follows, which can lead to weight gain
- 20. Essential Amino Acids • Plants are able to produce all the amino acids they need • Animals can only produce 11 of 20 essential amino acids because they lack some enzymes for synthesis of the other 9 amino acids. These amino acids are required in the diet of animals or protein deficiency will result.