How Cells Release Chemical Energy Chapter 6

Organelles where aerobic respiration produces energy molecule ATP Mitochondrial diseases affect body’s ability to meet energy needs Mitochondria

Photosynthesizers get light energy from the sun, store it as chemical energy, and produce ATP Animals eat plants or other animals and transform chemical energy to ATP ATP: Universal Energy Source

Making ATP Plants make ATP during photosynthesis Prokaryotes make ATP by fermentation Cells of most organisms make ATP by aerobic respiration of carbohydrates, fats, and protein

Summary Equation for Aerobic Respiration C 6 H 12 O 6 + 6O 2 6O 2 + 6H 2 O + ATP GLUCOSEOXYGEN CARBON DIOXIDE WATER

Overview of Aerobic Respiration CYTOPLASM Glycolysis Electron Transfer Phosphorylation Krebs Cycle ATP 2 CO 2 4 CO water 2 NADH 8 NADH 2 FADH 2 2 NADH 2 pyruvate e - + H + e - + oxygen (2 ATP net) glucose Typical Energy Yield: 36 ATP e-e- e - + H + ATP H+H+ e - + H + ATP 2 4

The Role of Coenzymes NAD + and FAD accept electrons and hydrogen Become NADH and FADH 2 Deliver electrons and hydrogen to the electron transfer chains

A simple sugar (C 6 H 12 O 6 ) Atoms held together by covalent bonds Glucose

glucose GYCOLYSIS pyruvate to second stage of aerobic respiration or to a different energy-releasing pathway Fig. 6-2, p.84

Glycolysis Occurs in Two Stages Energy-requiring steps –ATP energy activates glucose and its 6-carbon derivatives Energy-releasing steps –The products of the first part are split into 3-carbon pyruvate molecules –ATP and NADH form

Glycolysis: Net Energy Yield Energy requiring steps: 2 ATP used Energy releasing steps: 2 NADH formed 4 ATP formed Net yield: 2 ATP + 2 NADH

Mitochondria

Second Stage Reactions glucose GLYCOLYSIS pyruvate KREBS CYCLE ELECTRON TRANSFER PHOSPHORYLATION

Second Stage Reactions Preparatory reactions –Pyruvate is oxidized into 2-carbon acetyl- CoA + CO 2 –NAD + is reduced Krebs cycle –Acetyl-CoA is oxidized to two CO 2 –NAD + and FAD are reduced

Preparatory Reactions pyruvate NAD + NADH coenzyme A (CoA) OO carbon dioxide CoA acetyl-CoA

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

Results of the Second Stage All of the carbon molecules in pyruvate end up in CO 2 Coenzymes are reduced (they pick up electrons and hydrogen) One molecule of ATP is formed 4-carbon oxaloacetate is regenerated

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

Third Stage glucose GLYCOLYSIS pyruvate KREBS CYCLE ELECTRON TRANSFER PHOSPHORYLATION

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

glucose Glycolysis e–e– oxygen accepts “spent” electrons Electron Transfer phosphorylation 2 PGAL 2 pyruvate 2 NADH 2 CO 2 ATP 2 FADH 2 H+H+ 2 NADH 6 NADH 2 FADH 2 2 acetyl- CoA ATP 2 Krebs Cycle 4CO 2 ATP 32 ADP + P i H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ 2 4 Fig. 6-5 p.87 2 NAD +

Creating an H + Gradient NADH OUTER COMPARTMENT INNER COMPARTMENT

Making ATP ATP ADP + P i INNER COMPARTMENT

Importance of Oxygen Electron transport phosphorylation requires oxygen 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 –2 ATP formed by substrate-level phosphorylation Krebs cycle and preparatory reactions –2 ATP formed by substrate-level phosphorylation Electron transport phosphorylation –32 ATP formed

Anaerobic Pathways Alcoholic Fermentation

Fermentation Pathways Begin with glycolysis Are anaerobic: don’t require oxygen Yield only 2 ATP from glycolysis Steps after glycolysis only regenerate NAD +