1. Essential Knowledge 2.A.2: Organisms capture and store free energy for use in biological processes

2.  What can heterotrophs use to produce free energy? ◦ Heterotrophs can metabolize carbohydrates, lipids and proteins by hydrolysis Proteins Carbohydrates Amino acids Sugars Fats GlycerolFatty acids Glycolysis Glucose Glyceraldehyde-3- Pyruvate P NH 3 Acetyl CoA Citric acid cycle Oxidative phosphorylation

3.  Why are we talking about electron acceptors? ◦ Transferring electrons during a chemical reaction releases energy stored in organic molecules. This energy can be used to make ATP  What are the electron acceptors of cellular respiration? ◦ NADH – Glycolysis and Krebs cycle ◦ FADH 2 - Krebs cycle

4.  What do we call chemical reactions that involve the transfer of electrons? ◦ Oxidation-Reduction Reactions ◦ Redox Reactions  When is a substance oxidized? When is it reduced? ◦ The substance that is donating the electrons is “Oxidized” ◦ The substance that is accepting the electrons is “Reduced” (reduced because it takes on –e)

5. becomes oxidized becomes reduced

6. becomes oxidized becomes reduced

7.  Why use electron acceptors at all? Why not make ATP directly from glucose? ◦ Using electron acceptors allow for controlled use of energy. If all energy were released at once, a great deal of energy would be lost in the form of heat. Slow release of energy involving electron acceptors allows for more efficient use of the energy. ◦ Reduced electron acceptors like NADH are a form of stored energy. ◦ NADH passes electrons onto an electron transport chain ◦ Electrons are pulled through the electron transport chain in a series of steps that release energy to produce ATP

8. Fig. 9-4 Dehydrogenase Reduction of NAD + Oxidation of NADH 2 e – + 2 H + 2 e – + H + NAD + + 2[H] NADH + H+H+ H+H+ Nicotinami de (oxidized form) Nicotinami de (reduced form)

9.  What is the ultimate electron acceptor in cellular respiration? ◦ Oxygen – which joins with Hydrogen to form water.

10. Free energy, G (a) Uncontrolled reaction H2OH2O H 2 + 1 / 2 O 2 Explosive release of heat and light energy (b) Cellular respiration Controlled release of energy for synthesis of ATP 2 H + + 2 e – 2 H + 1 / 2 O 2 (from food via NADH) ATP 1 / 2 O 2 2 H + 2 e – Electron transport chain H2OH2O

11.  Cellular respiration has three stages: ◦ Glycolysis (breaks down glucose into two molecules of pyruvate) ◦ The citric acid cycle (completes the breakdown of glucose) ◦ Oxidative phosphorylation (accounts for most of the ATP synthesis)

12.  Where does glycolysis take place? ◦ Cytoplasm  What occurs during glycolysis? ◦ Literally means “sugar splitting” ◦ 2 major phases  Energy investment phase (requires 2 ATP)  Energy payoff phase (produces 4 ATP, 2 NADH, and 2 Pyruvate)

13. Energy investment phase Glucose 2 ADP + 2 P 2 ATPused formed 4 ATP Energy payoff phase 4 ADP + 4 P 2 NAD + + 4 e – + 4 H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Glucose Net 4 ATP formed – 2 ATP used2 ATP 2 NAD + + 4 e – + 4 H + 2 NADH + 2 H +

14.  What is the process by which ATP is produced during glycolysis? ◦ Substrate Level Phosphorylation – direct transfer of phosphate from organic compound to ADP by an enzyme to make ATP Enzyme ADP P Substrate Enzyme ATP + Product

15. Fig. 9-9-4 Glucose ATP ADP Hexokinase Glucose-6-phosphate Phosphoglucoisomerase Fructose-6-phosphate ATP ADP Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate 1 2 3 4 5 Aldolase Isomerase Fructose- 1, 6- bisphosphate Dihydroxyacet one phosphate Glyceraldehy de- 3-phosphate 4 5

16. Fig. 9-9-9 Triose phosphate dehydrogenase 2 NAD + NADH 2 2 2 2 2 2 2 ADP 2 ATP Pyruvate Pyruvate kinase Phosphoenolpyruvate Enolase 2 H 2 O 2-Phosphoglycerate Phosphoglyceromutase 3-Phosphoglycerate Phosphoglycerokinase 2 ATP 2 ADP 1, 3-Bisphosphoglycerate + 2 H + 6 7 8 9 10 2 2 ADP 2 ATP Phosphoenolpyruvate Pyruvate kinase 2 Pyruvate 10 2 P i

17.  How does the process of glycolysis support the theory of evolution? ◦ Glycolysis is a metabolic pathway that has been conserved across all domains. ◦ Ancient prokaryotes probably used glycolysis to produce energy – no need for oxygen / little oxygen in atmosphere for cellular respiration ◦ It is the most widespread metabolic pathway among Earth’s organisms – suggesting that it evolved very early in the history of life