Cellular respiration

The process by which cells harvest the energy stored in foodCellular respiration1SAVING FOR A Rainy Day2Feel the Burn3How do living organisms fuel their actions? Cellular respiration: the big picture

4ATP

AdenineRibose3 Phosphate groups5ATP

ATPEnergyEnergyAdenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP)PartiallychargedbatteryFullychargedbattery6

GlucoseGlycolysis Krebs cycle ElectrontransportFermentation (without oxygen)Alcohol or lactic acidSection 9-1Chemical Pathways7Cellular Respiration: The Big PictureC6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP)

Glucose + Oxygen Carbon dioxide + Water + Energy (ATP)

8Cellular Respiration: The big picture

99All living organisms extract energy from the chemical bonds of molecules (which can be considered food) through a process called cellular respiration. To generate energy, fuels such as glucose and other carbohydrates, proteins, and fats are broken down in three steps: (1) glycolysis, (2) the Krebs cycle, and (3) the electron transport chain.

Figure 4-34 The steps of cellular respiration: from glucose to usable energy.

GlucoseGlycolysisCytoplasmPyruvic acidElectrons carried in NADHKrebs CycleElectrons carried in NADH and FADH2Electron Transport ChainMitochondrionCellular Respiration: The Big PictureMitochondrionSection 9-110Three-Step ProcessBiggest ATP payoff (90%) occurs during the electron transport chain.

1111Glycolysis (terribly inefficient) occurs in the cytoplasm; the Krebs cycle and the electron transport chain occur in the mitochondria. Acetyl-CoA production is a necessary preparatory step to the Krebs cycle.

Figure 4-34 The steps of cellular respiration: from glucose to usable energy.

Cellular RespirationSection 9-2Glucose(C6H1206)+Oxygen(02)GlycolysisKrebsCycleElectronTransportChainCarbon Dioxide(CO2)+Water(H2O)12Cellular RespirationRequires (1) fuel and (2) oxygen.

13Cellular Respiration

14In Humansour cells can extract some of the energy stored in the bonds of the food moleculesEnergy

Bonds

Molecules 15Aerobic Respiration the video

16Glycolysis is the universal energy-releasing pathwaysplitting (lysis) of sugar (glyco) all organisms on the planet

single-celled organisms - provide all of the energy they need

17Glycolysis is the universal energy-releasing pathway

18GlycolysisThree of the ten steps yield energy

High-energy electrons are transferred to NADHNet result:pyruvateATP molecules NADH molecules

19GlycolysisGlucose (6C) is broken down into 2 PGAL (Phosphoglyceraldehyde 3 Carbon molecules) Cost: 2 ATP

20Glycolysis2 PGAL (3C) are converted to 2 pyruvates Result: 4 ATP, 2 NADHnet ATP production = 2 ATP

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22How Glycolysis WorksAnimationAnimation

23Glycolysis: The Movie

24The Fate of PyruvateYeast: pyruvic acid is decarboxylated and reduced by NADH to form a molecule of carbon dioxide and one of ethanolaccounts for the bubbles and alcohol in, for examples, beer and champagne (alcoholic fermentation)process is energetically wasteful because so much of the free energy of glucose (~95%) remains in the alcohol (a good fuel!)Red blood cells and active muscles: pyruvic acid is reduced by NADH forming a molecule of lactic acid (lactic acid fermentation)process is energetically wasteful because so much free energy remains in the lactic acid moleculeMitochondria: pyruvic acid is oxidized completely to form CO2 & H2O (cellular respiration)~ 40% of energy in original glucose molecule is trapped in molecules of ATP

25Glycolysis is very inefficientPyruvate can be further metabolized to yield more energy26Answer: 426The mitochondrion27The Preparatory Phase to the Krebs Cycle

2828The two pyruvate molecules move into the mitochondria and then undergo three quick modifications that prepare them to be broken down in the Krebs cycle:Modification 1. Each pyruvate molecule passes some of its high-energy electrons to the energy-accepting molecule NAD+, building two molecules of NADH. Modification 2. Next, a carbon atom and two oxygen atoms are removed from each pyruvate molecule and released as carbon dioxide. The CO2 molecules diffuse out of the cell and, eventually, out of the organism. In humans, for example, these CO2 molecules pass into the bloodstream and are transported to the lungs, from which they are eventually exhaled. Modification 3. In the final step in the preparation for the Krebs cycle, a giant compound known as coenzyme A attaches itself to the remains of each pyruvate molecule, producing two molecules called acetyl-CoA. Each acetyl-CoA molecule is now ready to enter the Krebs cycle.

Figure 4-30 Preparations of pyruvate.The Conversion of Pyruvate to Acetyl Co-A for Entry Into the Krebs Cycle29glycolysis (cytoplasm), pyruvic acid interior of mitochondrion

The Conversion of Pyruvate to Acetyl Co-A for Entry Into the Kreb's Cycle2 NADH are generated 2 CO2 are released

30The Krebs Cycle extracts energy from sugar31

3232There are eight separate steps in the Krebs cycle. Three general outcomes are depicted here.Outcome 1. A new molecule is formed. Acetyl-CoA adds its two-carbon acetyl group to a molecule of the starting material of the Krebs cycle, a four-carbon molecule called oxaloacetate. This process creates a six-carbon molecule. Outcome 2. High-energy electron carriers (NADH) are made and carbon dioxide is exhaled. The six-carbon molecule then gives electrons to NAD+ to make the high-energy electron carrier NADH. The six-carbon molecule releases two carbon atoms along with four oxygen atoms to form two carbon dioxide molecules. This CO2 is carried by the bloodstream to the lungs from which it is exhaled into the atmosphere. Outcome 3. The starting material of the Krebs cycle is re-formed, ATP is generated, and more high-energy electron carriers are formed. After the CO2 is released, the four-carbon molecule that remains from the original pyruvate-oxaloacetate molecule formed in Outcome 1 is modified and rearranged to once again form oxaloacetate, the starting material of the Krebs cycle. In the process of this reorganization, one ATP molecule is generated and more electrons are passed to one familiar high-energy electron carrier, NADH, and a new one, FADH2. The formation of these high-energy electron carriers increases the energy yield of the Krebs cycle. One oxaloacetate is reformed, the cycle is ready to break down the second molecule of acetyl-CoA. Two turns of the cycle are necessary to completely dismantle our original molecule of glucose.

Figure 4-31 Overview of the Krebs cycle.The Krebs Cycle extracts energy from sugar6 NADH2 FADH22 ATP4 CO2 (to atmosphere)

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The Krebs Cycle extracts energy from sugar34

The Krebs Cycle extracts energy from sugar35AnimationKrebs: The Movie36

Krebs: The Movie (Part 2)37

the electron transport chain382 key features of mitochondria

the electron transport chain392 mitochondrial spaces higher concentrations of molecules in one area or the other

The bag-within-a-bag

4040Material inside the mitochondrion can lie in one of two spaces: (1) the intermembrane space, which is outside of the inner bag, or (2) the mitochondrial matrix, which is inside the inner bag. With two distinct regions separated by a membrane, the mitochondrion can create higher concentrations of molecules in one area or the other. And because a concentration gradient is a form of potential energymolecules move from the high concentration area to the low concentration area the way water rushes down a hillonce a gradient is created, the energy released as the gradient equalizes itself can be used to do work. In the electron transport chain, this energy is used to build the energy-rich molecule ATP.

Figure 4-32 A bag within a bag.

Follow the Electrons, as We Did in Photosynthesis#2) This proton concentration gradient represents a significant source of potential energy!4141Start with the electrons carried by NADH and FADH2.

Over-the-counter NADH pills provide energy to sufferers of chronic fatigue syndrome. Why might this be?

Figure 4-33 The big energy payoffProton Gradients and Potential Energy42Electron Transport: The Movie43

Electron Transport: The Movie (Part 2)44

45Figure 4-34 The steps of cellular respiration: from glucose to usable energy.Review of Cellular Respiration46Review AnimationEnergy is obtained from a molecule of glucose in a stepwise fashion. 47Answer: 247Plants have both chloroplasts and mitochondria. 48Answer: 348Alternative Pathways to Energy49Rapid, strenuous exertion

O2 deficiency Alternative Pathways to Energy50NAD+ /FAD+ halted

back-up method for breaking down sugarlactic acidAlternative Pathways to Energy Acquisition51

Animation: Lactic Acid FermentationAlternative Pathways to Energy Acquisition52Yeast

acetaldehyde

produce alcohol only in the absence of oxygenAlternative Pathways to Energy Acquisition53

Animation: Alcoholic Fermentation

5454With rapid, strenuous exertion, our bodies soon fall behind in delivering oxygen from the lungs to the bloodstream to the cells and finally to the mitochondria. Oxygen deficiency then limits the rate at which the mitochondria can break down fuel and produce ATP.This slowdown in ATP production occurs because the electron transport chain requires oxygen as the final acceptor of all the electrons that are generated during glycolysis and the Krebs cycle. If oxygen is in short supply, the electrons from NADH (and FADH2) have nowhere to go. Consequently, the regeneration of NAD+ (and FAD+) in the electron transport chain is halted, leaving no recipient for the high-energy electrons harvested from the breakdown of glucose and pyruvate, and the whole process of cellular respiration can grind to a stop. Organisms dont let this interruption last long, though; most have a back-up method for breaking down sugar.Among animals, there is one willing acceptor for the NADH electrons in the absence of oxygen: pyruvate, the end product of glycolysis. When pyruvate accepts the electrons, it forms lactic acid.

Figure 4-36 Energy production compared: with and without oxygen.

anaerobic respiration55Answer: 555

Cells can run on protein and fat as well as on glucose56564-17. Eating a complete diet: cells can run on protein and fat as well as on glucose.Evolution has built humans and other organisms with the metabolic machinery that allows them to extract energy and other valuable chemicals from proteins, fats, and a variety of carbohydrates.For that reason, we are able to consume and efficiently utilize meals comprising various combinations of molecules:Sugars: In the case of dietary sugars, many are polysaccharidesmultiple simple sugars linked togetherrather than solely the simple sugar glucose. Before they can be broken down by cellular respiration, the polysaccharides must first be separated by enzymes into glucose or related simple sugars that can be broken down by cellular respiration. Lipids: Dietary lipids are broken down into their two constituent parts: a glycerol molecule and a fatty acid. The glycerol is chemically modified into one of the molecules produced during one of the ten steps of glycolysis. It then enters glycolysis at that step in the process and is broken down to yield energy. The fatty acids, meanwhile, are chemically modified into acetyl-CoA, at which point they enter the Krebs cycle. Proteins: Proteins are chains of amino acids. Upon consumption they are broken down chemically into their constituent amino acids. Once that is done, each amino acid is broken down into (1) an amino group that may be used in the production of tissue or excreted in the urine and (2) a carbon compound that is converted into one of the intermediate compounds in glycolysis or the Krebs cycle, allowing the energy stored in its chemical bonds to be harnessed.