California Science Standards #1f, 1g, 1i, 6d, 9a 1 Cellular Respiration Extracting energy from Organic compounds (food)

2 What do we know? Photosynthesis – Occurs in autotrophs – Stores ENERGY – Produces glucose – CO 2 + H 2 O C 6 H 12 O 6 + O 2 Cellular respiration – Occurs in autotrophs and heterotrophs – Releases ENERGY – Uses glucose – C 6 H 12 O 6 + O 2 CO 2 + H 2 0

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4 Respiration is a combustion reaction Like the burning snack foods, the “burning” of food molecules (glucose) in cells produces CO 2 and H 2 0, and it is an exothermic process. In exothermic reactions, the reactants contain more energy before the reaction than the products contain at the end of the reaction. (i.e: energy is released.)

5 Some key differences In the lab, the combustion released energy as heat (which increased the temp of the water in the test tube). This reaction occurred very quickly. – A cell cannot use heat to do cellular work, not to mention the fact that this large increase in temp would be dangerous!

6 Respiration “slows down” the combustion of glucose The energy from glucose is released slowly by many enzyme-catalyzed reactions during cell respiration. This released energy is used to make ATP.

7 Respiration uses energy stored in glucose to make ATP ATP is adenosine triphosphate and is the main stored form of energy in all cells ATP contains three phosphate groups (see pic: the negative charges repel one another so the ATP is “unstable”). When one is removed, energy is released. The released energy from ATP is used for cellular work.

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9 ATP: The energy “currency” of a cell. All cellular work comes at the “expense” of ATP.

10 Cellular Respiration An Overview (“Map”) ATP

11 Glycolysis First step of cellular respiration; occurs in the cytoplasm. Breaks apart 1 glucose molecule (6-C) into 2 pyruvic acid molecules (3-C each) Requires glucose and 2 ATP Produces pyruvic acid /pyruvate, NADH, and 2 ATP (net yield) – Pyruvic acid used later in Krebs cycle – NADH (transports electrons) used in electron transport chain (ETC)

12 Glucose 6-carbon compound 2 molecules of PGAL 2 molecules of 3-C compound 2 molecules of pyruvic acid STEP 1 STEP 2 STEP 3 STEP 4 CCCCCCCCCCCC PP CCCPCCCP CCCPPCCCPP CCCCCC -2 ATP 2 NADH 4 ATP

13 Cellular Respiration Check the Map… ATP

14 Aerobic Respiration (one branch of cellular respiration) Requires oxygen Produces nearly 20x more ATP than is produced by glycolysis alone 2 major stages: – Krebs cycle – Electron transport chain Location: Mitochondria Begins with pyruvic acid that is modified to become acetyl-CoA

15 Krebs Cycle Occurs in the mitochondrial matrix Acetyl CoA binds to oxaloacetic acid producing citric acid. In reactions, the hydrogens are “stripped” off the organic compounds, releasing carbons as CO 2 (waste). Produces CO 2, NADH, FADH 2, and 2 ATP

16 Citric acid CCCCCC Oxaloacetic acid CCCC CC 4-C compound CCCC C ATP NADH 5-C compound CCCCC C NADH 4-C compound CCCC FADH 2 Krebs Cycle

17 Electron Transport Chain Last stage of aerobic respiration Located on inner membrane folds (cristae) of mitochondrion cristae

18 Electron transport chain is here (Mitochondrial Matrix - Location of R&P of Krebs Cycle )

19 a.k.a ATP synthase (ETS)

20 Electron Transport, continued NADH and FADH 2 contain high energy electrons. When NADH and FADH 2 reach the ETC they lose H+ and e-. Their high-energy e- are passed along the ETC, and energy from the e- is used to pump H + (protons) to the outer compartment of the mitochondrion. Energy from diffusion of H + back into the matrix is used to generate 34 ATP molecules (chemiosmosis)

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22 ATP Synthase

23 Let’s Review the Summary Equation C 6 H 12 O 6 + O 2 CO 2 + H 2 0 – Glucose used in glycolysis – CO 2 produced in Krebs cycle (completing the breakdown of glucose) What is the importance of Oxygen? – There must be a “final acceptor” of e- at the end of the ETC. If the last protein in the chain holds onto the e- there will be a “traffic jam” and no other e- will flow down the chain. – Result: H+ pumping stops, so H+ gradient disappears and there is no energy to drive the synthesis of ATP. – Oxygen is the final e- acceptor of the ETC, so it keeps the ETC “running”.

24 So oxygen is used in the ETC and this is where water is formed. – When oxygen accepts the e-, it also bonds with H+ to form H 2 O.

25 Total ATP From Cellular Respiration 34

26 Cellular Respiration Check the Map… ATP

27 Fermentation (Anaerobic Respiration) No oxygen? No problem…(kind of) 2 types: lactic acid fermentation, alcoholic fermentation Pros: can regenerate NAD+ when short on O 2 – Keeps glycolysis going (small net gain of ATP) Cons: Cannot produce additional ATP – Only unicellular organisms, like bacteria or yeast, can survive with the ATP made by glycolysis alone. – Some cells in multicellular organisms can switch to anaerobic respiration, but only for a short time.

28 Lactic Acid Fermentation Manufacture of yogurt, cheese Muscle cells – “Anaerobic exercise” (sprints) – Lactic acid build-up (muscle burn, fatigue, cramps) Pyruvic acid Lactic acid Glucose CCCCCCCCCCCC NAD+NADH + H+

29 Alcoholic Fermentation Basis of wine and beer industries – Yeast + fruit juice = alcohol Takes place when making bread – CO 2 makes bread rise; alcohol evaporates Pyruvic acid Ethyl alcohol Glucose CCCCCCCCCCC NAD+NADH + H+ 2-C compound CC C CO 2