Copyright © 2009 Pearson Education, Inc. Lectures by Gregory Ahearn University of North Florida Chapter 7 Harvesting Energy: Glycolysis and Cellular Respiration

Copyright © 2009 Pearson Education Inc. 7.1 What Is The Source Of A Cell’s Energy?  The energy for cellular activities is stored until use in _________ of molecules such as carbohydrates and fats.  In order to be used, stored energy is transferred to the bonds of energy-carrier molecules such as adenosine triphosphate (ATP).  _________ is a key energy-storage molecule, and energy stored in this molecule is harvested to power many biological processes in cells.

Copyright © 2009 Pearson Education Inc. 7.1 What Is The Source Of A Cell’s Energy?  Photosynthesis is the ultimate source of cellular energy.  Photosynthetic cells capture and store sunlight energy, and this energy is later used by cells.  These cells can be the photosynthetic organisms themselves, or can be other organisms that directly or indirectly consume photosynthesizers.

Copyright © 2009 Pearson Education Inc. 7.1 What Is The Source Of A Cell’s Energy?  ___________ metabolism and ____________ are complementary processes.  The products of each reaction provide reactants for the other.  The symmetry is apparent by comparing the equations that describe each process. Photosynthesis: 6 CO 2 + 6H 2 O + sunlight energy  C 6 H 12 O O 2 Complete glucose metabolism: C 6 H 12 O 6 + 6O 2  6 CO H ATP + heat energy

Copyright © 2009 Pearson Education Inc. 7.2 How Do Cells Harvest Energy From Glucose?  Glucose metabolism occurs in stages; the first stage is glycolysis. Glycolysis occurs in the ___________ of cells. Glucose (a six-carbon sugar) is split into two three-carbon _______ molecules. The split releases a small amount of energy that is used to make _____ ATP molecules.

Copyright © 2009 Pearson Education Inc. Fig. 7-1 O2O2 2 (mitochondrion) H2OH2O electron carriers 4 CO 2 2 acetyl CoA 32 or 34 intermembrane compartment Electron transport chain 2 CO 2 Krebs cycle glucose Glycolysis (cytoplasmic fluid) 2 pyruvate lactate 2 or + 2 Fermentation 2 2 ethanol CO 2 Cellular respiration ATP CCCCCC C C C C C C CC C C C C C

Copyright © 2009 Pearson Education Inc. 7.2 How Do Cells Harvest Energy From Glucose?  Pyruvate produced by glycolysis is further processed in the second stage, called cellular ______________.  Cellular respiration occurs in the _______________.  Cellular respiration breaks pyruvate down to CO 2 and H 2 0, yielding 34 or 36 ATP molecules.  ____________ is needed for cellular respiration to proceed.

Copyright © 2009 Pearson Education Inc. 7.2 How Do Cells Harvest Energy From Glucose?  When oxygen is not available, the second stage of glucose metabolism is ____________.  In the absence of oxygen, pyruvate remains in the cytoplasm.  Cytoplasmic pyruvate may be converted to _________ or _________ by fermentation.  Fermentation does not produce additional ATP energy.

Copyright © 2009 Pearson Education Inc. 7.3 What Happens During Glycolysis?  Glycolysis splits one molecule of glucose into two molecules of pyruvate.  During glycolysis, one molecule of glucose yields two ATP and two molecules of the electron carrier nicotinamide adenine dinucleotide (NADH).  Glycolysis involves two major parts: Glucose activation Energy harvest

Copyright © 2009 Pearson Education Inc. glucose fructose bisphosphate 2 2 Glucose activation1 ATPADP CCC CCC CCC CCC PP 7.3 What Happens During Glycolysis?  Glucose activation The activation of glucose uses up some ATP energy. Two ATP molecules are used to phosphorylate glucose to form fructose bisphosphate. Fig

Copyright © 2009 Pearson Education Inc. 7.3 What Happens During Glycolysis?  Energy harvest from glycolysis Two molecules of fructose bisphosphate split into two glyceraldehyde-3-phosphate (G 3 P) molecules. Each G 3 P molecule is converted to pyruvate. Fig G3P pyruvate Energy harvest2 NAD + ADP NADH ATP CCC CCC P

Copyright © 2009 Pearson Education Inc. 7.3 What Happens During Glycolysis?  The essentials of glycolysis glucose fructose bisphosphate G3P pyruvate Energy harvestGlucose activation12 NAD + ADP ATPADP NADH ATP CCC CCC CCC CCC CCC CCC PP P Two ATPs are used to activate glucose. Two ATPs are made for each pyruvate (four total). Each conversion to pyruvate forms one molecule of NADH (two total). Net gain from glycolysis: 2ATP + 2 NADH

Copyright © 2009 Pearson Education Inc. 7.4 What Happens During Cellular Respiration?  Cellular respiration is the second stage of glucose metabolism, and it occurs only in the presence of oxygen.  Cellular respiration occurs in the mitochondria.  Large amounts of ATP are produced by this process, which converts pyruvate to CO 2 and H 2 O.

Copyright © 2009 Pearson Education Inc. Fig. 7-3 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP cristae Krebs cycle outer membrane electron transport chain matrix intermembrane compartment inner membrane (cytoplasmic fluid) mitochondrion outer membrane inner membrane coenzyme A (matrix) Glycolysis glucose 2 pyruvate ATP-synthesizing enzyme CO 2 2e – 2 H + 1/2 O 2 energized electron carriers: NADH, FADH 2 depleted carriers: NAD +, FAD H2OH2O acetyl CoA ATP ADP

Copyright © 2009 Pearson Education Inc. 7.4 What Happens During Cellular Respiration? Steps of cellular respiration: Step 1: Two molecules of pyruvate produced by glycolysis are transported into the matrix of a mitochondrion. Step 2: Each pyruvate is split into CO 2 and acetyl CoA, which enters the Krebs cycle. The Krebs cycle produces one ATP from each pyruvate, and donates electrons to NADH and flavin adenine dinucleotide (FADH 2 ).

Copyright © 2009 Pearson Education Inc. 7.4 What Happens During Cellular Respiration? Step 3: NADH and FADH 2 donate energized electrons to the electron transport chain of the inner membrane. Step 4: In the electron transport chain, electron energy is used to transport hydrogen ions (H + ) from the matrix to the intermembrane compartment. Step 5: Electrons combine with O 2 and H + to form H 2 O.

Copyright © 2009 Pearson Education Inc. 7.4 What Happens During Cellular Respiration? Step 6: Hydrogen ions in the intermembrane compartment diffuse across the inner membrane, down their concentration gradient. Step 7: The flow of ions into the matrix provides the energy to produce ATP from ADP. Step 8: ATP moves out of mitochondrion into the cytoplasm.

Copyright © 2009 Pearson Education Inc. 7.4 What Happens During Cellular Respiration?  The Krebs cycle breaks down pyruvate in the mitochondrial matrix. Pyruvate produced by glycolysis reaches the matrix and reacts with coenzyme A, forming acetyl CoA. During this reaction, two electrons and a H + are transferred to NAD + to form NADH. Acetyl CoA enters the Krebs cycle and produces one ATP, one FADH 2, and three NADH.

Copyright © 2009 Pearson Education Inc. 7.4 What Happens During Cellular Respiration?  The reactions in the mitochondrial matrix Fig. 7-4 CoA acetyl CoA CO 2 pyruvate CO 2 2 coenzyme A 3 3 Formation of acetyl CoA Krebs cycle 2 1 ATP ADP FADH 2 NAD + NADH FAD NAD + NADH C C C C C C C

Copyright © 2009 Pearson Education Inc. 7.4 What Happens During Cellular Respiration?  Energetic electrons are carried to the electron transport chain. Step 1: Energized carriers deposit their electrons in the electron transport chains (ETC) in the inner mitochondrial membrane. Step 2: Electrons in the ETC move from one molecule to the next, transferring energy that is used to pump H + out of the matrix and into the intermembrane compartment. Step 3: At the end of the ETC, oxygen atoms combine with two H + and two depleted electrons to form H 2 O.

Copyright © 2009 Pearson Education Inc. 7.4 What Happens During Cellular Respiration? Oxygen accepts electrons after they have passed through the ETC and given up most of their energy. If O 2 is not present, electrons accumulate in the ETC, H + pumping out of the matrix stops, and cellular respiration ceases.

Copyright © 2009 Pearson Education Inc. H+H+ H2OH2O (inner membrane) (intermembrane compartment) (matrix) energy to drive synthesis electron carriers H+H+ 2e – H+H+ 1/2 O 2 + 2H + ATP NADH FADH 2 NAD + FAD What Happens During Cellular Respiration?  The electron transport chain in the mitochondrial matrix Fig. 7-5

Copyright © 2009 Pearson Education Inc. 7.4 What Happens During Cellular Respiration?  Energy from a hydrogen-ion gradient is used to produce ATP. Hydrogen ions accumulate in the intermembrane compartment and diffuse back into the matrix. The energy released when hydrogen ions move down their concentration gradient is used to make ATP in a process called chemiosmosis. During chemiosmosis, 32 to 34 molecules of ATP are produced from each molecule of glucose. This ATP is transported from the matrix to the cytoplasm, where it is used to power metabolic reactions.

Copyright © 2009 Pearson Education Inc. 7.5 What Happens During Fermentation?  When oxygen is not present (anaerobic conditions), glucose cannot be metabolized by cellular respiration; instead, fermentation takes place.  Unlike cellular respiration, fermentation generates no ATP, but instead, regenerates NAD + that is used to get ATP from glycolysis.  pyruvate acts as an electron acceptor from the NADH produced during glycolysis.  When pyruvate accepts electrons from NADH, it recycles the NAD + so that more glucose can be converted to pyruvate, generating a small amount of ATP in the process.  When no O 2 is present, glycolysis becomes the main source of ATP and NADH production.

Copyright © 2009 Pearson Education Inc. 7.5 What Happens During Fermentation?  There are two types of fermentation: one converts pyruvate to ethanol and CO 2, and the other converts pyruvate to lactate. Alcoholic fermentation is the primary mode of metabolism in many microorganisms. The reactions use hydrogen ions and electrons from NADH, thereby regenerating NAD +. Alcoholic fermentation is responsible for the production of many economic products, such as wine, beer, and bread.

Copyright © 2009 Pearson Education Inc. glucose pyruvateethanolCO 2 (fermentation)(glycolysis) 2+ 2 NADH NAD + ATPADP C C C C C C C C C C C C 7.5 What Happens During Fermentation?  Glycolysis followed by alcoholic fermentation Fig. 7-6

Copyright © 2009 Pearson Education Inc. 7.5 What Happens During Fermentation?  Other cells ferment pyruvate to lactate, and include microorganisms that produce yogurt, sour cream, and cheese.  Lactate fermentation also occurs in aerobic organisms when cells are temporarily deprived of oxygen, such as muscle cells during vigorous exercise.  These muscle cells ferment pyruvate to lactate, which uses H + and electrons from NADH to regenerate NAD +.

Copyright © 2009 Pearson Education Inc. glucose pyruvatelactate (fermentation)(glycolysis) 2 NADH NAD + ATP ADP C C C C C C C C C C C C 7.5 What Happens During Fermentation?  Glycolysis followed by lactate fermentation Fig. 7-8