1 How Cells Harvest Energy Chapter 9

2 Outline Cellular Energy Harvest Cellular Respiration – Glycolysis – Oxidation of Pyruvate – Krebs Cycle – Electron Transport Chain Catabolism of Protein and Fat Fermentation Evolution of Metabolism

3 Chemical Energy to Drive Metabolism Autotrophs harvest sunlight and convert radiant energy into chemical energy. Heterotrophs live off the energy produced by autotrophs. – extract energy from food via digestion and catabolism

4 Cellular Respiration Cells harvest energy by breaking bonds and shifting electrons from one molecule to another. – aerobic respiration - final electron acceptor is oxygen – anaerobic respiration - final electron acceptor is inorganic molecule other than oxygen – fermentation - final electron acceptor is an organic molecule

5 ATP Adenosine Triphosphate (ATP) is the energy currency of the cell. – used to drive movement – used to drive endergonic reactions

6 ATP Most of the ATP produced in cells is made by the enzyme ATP synthase. – Enzyme is embedded in the membrane and provides a channel through which protons can cross the membrane down their concentration gradient.  ATP synthesis is achieved by a rotary motor driven by a gradient of protons.

7 Glucose Catabolism Cells catabolize organic molecules and produce ATP in two ways: – substrate-level phosphorylation – aerobic respiration  in most organisms, both are combined  glycolysis  pyruvate oxidation  Krebs cycle  electron transport chain

8 Aerobic Respiration

9 Stage One - Glycolysis For each molecule of glucose that passes through glycolysis, the cell nets two ATP molecules. Priming – glucose priming – cleavage and rearrangement Substrate-level phosphorylation – oxidation – ATP generation

10 Priming Reactions

11 Cleavage Reactions

12 Energy-Harvesting Reactions

13 Recycling NADH As long as food molecules are available to be converted into glucose, a cell can produce ATP. – Continual production creates NADH accumulation and NAD + depletion.  NADH must be recycled into NAD +.  aerobic respiration  fermentation

14 Recycling NADH

15 Stage Two - Oxidation of Pyruvate Within mitochondria, pyruvate is decarboxylated, yielding acetyl-CoA, NADH, and CO 2.

16 Stage Three - Krebs Cycle Acetyl-CoA is oxidized in a series of nine reactions. – two steps:  priming  energy extraction

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18 Krebs Cycle 1: Condensation 2-3: Isomerization 4: First oxidation 5: Second oxidation 6: Substrate-level phosphorylation 7: Third oxidation 8-9: Regeneration and oxaloacetate

19 Harvesting Energy by Extracting Electrons Glucose catabolism involves a series of oxidation-reduction reactions that release energy by repositioning electrons closer to oxygen atoms. – Energy is harvested from glucose molecules in gradual steps, using NAD + as an electron carrier.

20 Electron Transport

21 Stage Four: The Electron Transport Chain NADH molecules carry electrons to the inner mitochondrial membrane, where they transfer electrons to a series of membrane- associated proteins.

22 Electron Transport Chain

23 Chemiosmosis

24 Theoretical ATP Yield of Aerobic Respiration

25 Regulating Aerobic Respiration Control of glucose catabolism occurs at two key points in the catabolic pathway. – glycolysis - phosphofructokinase – Krebs cycle - citrate synthetase

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27 Control of Glucose Catabolism

28 Catabolism of Proteins and Fats Proteins are utilized by deaminating their amino acids, and then metabolizing the product. Fats are utilized by beta-oxidation.

29 Cellular Extraction of Chemical Energy

30 Fermentation Electrons that result from the glycolytic breakdown of glucose are donated to an organic molecule. – regenerates NAD + from NADH  ethanol fermentation  lactic acid fermentation

31 Evolution of Cellular Respiration degradation glycolysis anaerobic photosynthesis oxygen-forming photosynthesis nitrogen fixation aerobic respiration

32 Summary Cellular Energy Harvest Cellular Respiration – Glycolysis – Oxidation of Pyruvate – Krebs Cycle – Electron Transport Chain Catabolism of Protein and Fat Fermentation Evolution of Metabolism

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