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HOW CELLS HARVEST CHEMICAL ENERGY (CELLULAR RESPIRATION)

Important points to review…. Energy is one-way flow. Energy is not created or destroyed it can only be converted from one form to another. Solar energy Chemical energy (sun) (stored in glucose molecule) Overview Photosynthesis Reaction: 6CO H 2 O C 6 H 12 O 6 + 6O H 2 O

2nd Important Energy Reaction Overview Cellular Respiration Reaction: C 6 H 12 O 6 + 6O2 6CO H 2 O + (32 ATP) Cellular respiration is an exergonic process that transfers energy from the bonds in glucose to form ATP.

Photosynthesis and cellular respiration provide energy for life - 4 important points © 2012 Pearson Education, Inc.

Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts Cellular respiration in mitochondria (for cellular work) Heat energy Glucose CO 2 H2OH2O O2O2 ATP The connection between photosynthesis and cellular respiration

Breathing Lungs Bloodstream CO 2 O2O2 O2O2 Muscle cells carrying out Cellular Respiration Glucose  O 2 CO 2  H 2 O  ATP The connection between breathing and cellular respiration Breathing supplies O 2 for use in cellular respiration and removes CO 2

CONNECTION: The human body uses energy from ATP for all its activities  The average adult human needs about 2,200 kcal ( the same as a food Calorie ) of energy per day. –About 75% of these calories are used to maintain a healthy body. –The remaining 25% is used to power physical activities.

Cells tap energy from electrons “falling” from organic fuels to oxygen  The energy necessary for life is contained in the arrangement of electrons in chemical bonds in organic molecules.  An important question is how do cells extract this energy? –When the carbon-hydrogen bonds of glucose are broken, electrons are transferred to oxygen. –Oxygen has a strong tendency to attract electrons. –An electron loses potential energy when it “falls” slowly to oxygen. That energy can be picked up by ATP!

Cells tap energy from electrons “falling” from organic fuels to oxygen  Energy can be released from glucose by simply burning it.  The energy is dissipated as heat and light and is not available to living organisms.  On the other hand, cellular respiration is the controlled breakdown of organic molecules.  Summation: Energy is –___________________________________

Cells tap energy from electrons “falling” from organic fuels to oxygen  The movement of electrons from one molecule to another is an oxidation-reduction reaction, or redox reaction.

Cells tap energy from electrons “falling” from organic fuels (glucose) to oxygen  Enzymes are necessary to oxidize glucose and other foods.  NAD + –is an important enzyme in oxidizing glucose, –accepts electrons, and –becomes reduced to NADH.

Cells tap energy from electrons “falling” from organic fuels to oxygen  There are other electron “carrier” molecules that function like NAD +. –They form a staircase where the electrons pass from one to the next down the staircase. –These electron carriers collectively are called the electron transport chain. –As electrons are transported down the chain, ATP is generated.

Overview: Cellular respiration occurs in three main stages  Cellular respiration consists of a sequence of steps that can be divided into three stages. –Stage 1 – ______________________ –Stage 2 – ______________ and ___________________ –Stage 3 – ______________________

Mitochondria

Overview: Cellular respiration occurs in three main stages  Stage 1: Glycolysis 

Glycolysis harvests chemical energy by oxidizing glucose to pyruvate  In glycolysis, –a single molecule of ____________ is enzymatically cut in half through a series of steps, –two molecules of _____________ are produced, –two molecules of NAD + are reduced to two molecules of ____________, and –a net of two molecules of _________ is produced.

6 1,3-Bisphospho- glycerate 3-Phospho- glycerate 2-Phospho- glycerate Phosphoenol- pyruvate (PEP) Pyruvate NADH NAD  HH HH ADP ATP H2OH2O H2OH2O P P P P P P P P P P P P P P

Glycolysis harvests chemical energy by oxidizing glucose to pyruvate  The steps of glycolysis can be grouped into two main phases. –In steps 1–4, the energy investment phase, –energy is consumed as two ATP molecules are used to energize a glucose molecule, –which is then split into two small sugars that are now primed to release energy. –In steps 5–9, the energy payoff, –two NADH molecules are produced for each initial glucose molecule and –4 ATP molecules are generated. (net gain of 2!)

Glycolysis harvests chemical energy by oxidizing glucose to pyruvate  ATP is formed in glycolysis by substrate-level phosphorylation during which –an enzyme transfers a ____________ group from a substrate molecule to ADP and –ATP is formed.

Overview: Cellular respiration occurs in three main stages  Stage 2: The citric acid cycle 

Pyruvate is oxidized prior to the citric acid cycle  Two molecules of pyruvate are produced for each molecule of glucose that enters glycolysis.  Pyruvate does not enter the citric acid cycle, but undergoes some chemical grooming in which –a carboxyl group is removed and given off as _______, –the two-carbon compound remaining is oxidized while a molecule of NAD + is reduced to __________, –coenzyme A joins with the two-carbon group to form acetyl coenzyme A, abbreviated as acetyl CoA, and –acetyl CoA enters the citric acid cycle.

The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH 2 molecules  The citric acid cycle –is also called the Krebs cycle (after the German-British researcher Hans Krebs, who worked out much of this pathway in the 1930s), –completes the oxidation of organic molecules (glucose), and –generates many NADH and FADH 2 molecules.

Acetyl CoA Citric Acid Cycle CoA CO NAD  3 H  NADH ADP ATP P FAD FADH 2 During the citric acid cycle the two-carbon group of acetyl CoA is added to a four-carbon compound, forming citrate, citrate is degraded back to the four-carbon compound, two CO 2 are released, and ___ ATP, ___ NADH, and __-FADH 2 are produced.

The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH 2 molecules  Remember that the citric acid cycle processes two molecules of acetyl CoA for each initial glucose.  Thus, after two turns of the citric acid cycle, the overall yield per glucose molecule is –2 ATP, –6 NADH, and –2 FADH 2.

NADH NAD  NADH HH HH HH CO 2 ATP ADP P FAD FADH 2 CoA Acetyl CoA Oxaloacetate Citric Acid Cycle 2 carbons enter cycle Citrate leaves cycle Alpha-ketoglutarate leaves cycle Succinate Malate Step Acetyl CoA stokes the furnace. Steps – NADH, ATP, and CO 2 are generated during redox reactions. Steps – Further redox reactions generate FADH 2 and more NADH.

Overview: Cellular respiration occurs in three main stages  Stage 3: Oxidative phosphorylation  Use _____________ and __________ already formed in previous stages  Produce ___ ___ ___

Most ATP production occurs by oxidative phosphorylation  Electrons from NADH and FADH 2 travel down the electron transport chain to ______.  Oxygen picks up H + to form water.  Energy released by these redox reactions is used to pump H + from the mitochondrial matrix into the intermembrane space.  In __________________, the H + diffuses back across the inner membrane through ________________complexes, driving the synthesis of ATP.

Oxidative Phosphorylation Electron Transport Chain Chemiosmosis Mito- chondrial matrix Inner mito- chondrial membrane Intermem- brane space Electron flow Protein complex of electron carriers Mobile electron carriers ATP synthase NADH NAD  2 H  FADH 2 FAD O2O2 H2OH2O ADP PATP 1 2 HH HH HH HH HH HH HH HH HH HH HH I II III IV

Review: Each molecule of glucose yields many molecules of ATP  Recall that the energy payoff of cellular respiration involves –glycolysis, –alteration of pyruvate, –the citric acid cycle, and –oxidative phosphorylation.  The total yield is about 32 ATP molecules per glucose molecule.  This is about 34% of the potential energy of a glucose molecule.  In addition to the ATP, _______and _______are produced.

Respiration RapCellular Respiration Rap

NADH FADH 2 NADH FADH 2 NADH or NADH Mitochondrion CYTOPLASM Electron shuttles across membrane Glycolysis Glucose 2 Pyruvate Pyruvate Oxidation 2 Acetyl CoA Citric Acid Cycle Oxidative Phosphorylation (electron transport and chemiosmosis) Maximum per glucose: by substrate-level phosphorylation by oxidative phosphorylation ATP  2 about  28 ATP About ATP32ATP  2

Respiration AnimationCellular Respiration Animation Watch it until it makes sense! Glycolysis - Fermentation Animation

Fermentation enables cells to produce ATP without oxygen  Fermentation is a way of harvesting chemical energy that does not require oxygen. Fermentation –takes advantage of glycolysis….so.. –produces _____ ATP molecules per glucose, and –reduces NAD + to _________.  The trick of fermentation is to provide an anaerobic path for recycling NADH back to NAD +.

Animation: Fermentation Overview Right click on animation / Click play Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation, in which NADH is oxidized to NAD + and pyruvate is reduced to lactate. The baking and winemaking industries have used alcohol fermentation for thousands of years. In this process yeasts (single-celled fungi)oxidize NADH back to NAD + and convert pyruvate to CO 2 and ethanol.

EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on Earth  Glycolysis is the universal energy-harvesting process of life.  The role of glycolysis in fermentation and respiration dates back to –life long before oxygen was present, –when only prokaryotes inhabited the Earth, –about 3.5 billion years ago.  The ancient history of glycolysis is supported by its –occurrence in all the domains of life and –location within the cell, using pathways that do not involve any membrane-bounded organelles.

Cells use many kinds of organic molecules as fuel for cellular respiration  Although glucose is considered to be the primary source of sugar for respiration and fermentation, ATP is generated using –carbohydrates, –fats, and –proteins. © 2012 Pearson Education, Inc.

Food, such as peanuts Sugars Glycerol Fatty acidsAmino acids Amino groups Oxidative Phosphorylation Citric Acid Cycle Pyruvate Oxidation Acetyl CoA ATP Glucose G3PPyruvate Glycolysis Carbohydrates Fats Proteins

Food molecules provide raw materials for biosynthesis  Cells use intermediates from cellular respiration for the biosynthesis of other organic molecules.

You should now be able to 1.Compare the processes and locations of cellular respiration and photosynthesis. 2.Explain how breathing and cellular respiration are related. 3.Provide the overall chemical equation for cellular respiration. 4.Explain how the human body uses its daily supply of ATP.

You should now be able to 5.Explain how the energy in a glucose molecule is released during cellular respiration. 6.Describe the general roles of dehydrogenase, NADH, and the electron transport chain in cellular respiration. 7.Compare the reactants, products, and energy yield of the three stages of cellular respiration.

You should now be able to 9.Compare the reactants, products, and energy yield of alcohol and lactic acid fermentation. 10.Briefly explain how carbohydrates, fats, and proteins are used as fuel for cellular respiration.

Aerobic respiration…… an animation to help you visualize

cellular work chemiosmosis H  gradient glucose and organic fuels Cellular respiration generates has three stagesoxidizes uses produce some produces many to pull electrons down H  diffuse through ATP synthase pumps H  to create uses by a process called energy for (a) (b) (c) (d) (e) (f) (g) to

Proton Pump/Chemiosmosis

AN OVERVIEW OF AEROBIC RESPIRATION