Chapter 6 How Cells Harvest Chemical Energy Overview: Cellular Respiration Reactions involved in cellular respiration Glycolysis Krebs Cycle Electron Transport

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  • Chapter 6 How Cells Harvest Chemical EnergyOverview: Cellular RespirationReactions involved in cellular respiration GlycolysisKrebs CycleElectron TransportFermentationFood used to produce ATPATP used to produce food

  • Nearly all the cells in our body break down sugars for ATP productionCellular respiration occurs in mitochondriaCellular respiration is a chemical process that harvests energy from organic moleculesCellular respiration yields CO2, H2O, and a large amount of ATPINTRODUCTION TO CELLULAR RESPIRATIONPhotosynthesis and cellular respiration provide energy for life

  • The ingredients for photosynthesis are carbon dioxide and waterCO2 is obtained from the air by a plants leavesH2O is obtained from the damp soil by a plants rootsChloroplasts rearrange the atoms of these ingredients to produce sugars (glucose) and other organic moleculesOxygen gas is a by-product of photosynthesis

  • The Relationship Between Cellular Respiration and BreathingCellular respiration and breathing are closely relatedCellular respiration requires a cell to exchange gases with its surroundingsBreathing exchanges these gases between the blood and outside air

  • Cellular respiration banks (stores)energy in ATP moleculesCellular respiration breaks down glucose molecules and banks their energy in ATPThe process uses O2 and releases CO2 and H2O GlucoseOxygen gasCarbon dioxideWaterEnergy

  • Connection: The human body uses energy from ATP for all its activitiesATP powers almost all cell and body activitiesA calorie is the amount of energy that raises the temperature of 1 gram of water by 1 degree Celsius

  • Cells tap energy from electrons transferred from organic fuels to oxygenGlucose gives up energy as it is oxidizedLoss of hydrogen atomsGlucoseGain of hydrogen atomsEnergy

  • Redox ReactionsChemical reactions that transfer electrons from one substance to another are called oxidation-reduction reactionsRedox reactions for shortThe loss of electrons during a redox reaction is called oxidationThe acceptance of electrons during a redox reaction is called reduction

  • [Oxygen gains electrons (and hydrogens)]Oxidation[Glucose loses electrons (and hydrogens)]GlucoseOxygenCarbondioxideWaterReduction

  • Why does electron transfer to oxygen release energy?When electrons move from glucose to oxygen, it is as though they were fallingThis fall of electrons releases energy during cellular respiration

  • NADH and Electron Transport ChainsThe path that electrons take on their way down from glucose to oxygen involves many stopsAn enzyme called dehydrogenase and a coenzyme called NAD+ (nicotinamide adenine dinucleotide) play important role in oxidizing glucose.

  • The first stop is an electron acceptor called NAD+The transfer of electrons from organic fuel to NAD+ reduces it to NADHThe rest of the path consists of an electron transport chainThis chain involves a series of redox reactionsThese lead ultimately to the production of large amounts of ATP

  • All of the reactions involved in cellular respiration can be grouped into three main stagesGlycolysisThe Krebs cycleElectron transport

  • Stage 1: GlycolysisA molecule of glucose is split into two molecules of pyruvic acidGlycolysis breaks a six-carbon glucose into two three-carbon moleculesThese molecules then donate high energy electrons to NAD+, forming NADHGlycolysis occurs in the cytoplasm

  • Glycolysis makes some ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP (This process is called substrate-level phosphorylation)Enzyme

  • Stage 2: The Krebs CycleThe Krebs cycle completes the breakdown of sugarIn the Krebs cycle, pyruvic acid from glycolysis is first prepped into a usable form, Acetyl-CoA

  • The Krebs cycle extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2The cycle uses some of this energy to make ATPThe cycle also forms NADH and FADH2The Krebs cycle and the electron transport chain occur in the mitochondria

  • Stage 3: Electron TransportElectron transport releases the energy your cells need to make the most of their ATPThe molecules of electron transport chains are built into the inner membranes of mitochondriaThe chain functions as a chemical machine that uses energy released by the fall of electrons to pump hydrogen ions across the inner mitochondrial membraneThese ions store potential energy

  • When the hydrogen ions flow back through the membrane, they release energyThe ions flow through ATP synthaseATP synthase takes the energy from this flow and synthesizes ATP

  • The electrons from NADH and FADH2 travel down the electron transport chain to oxygen Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranesIn chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP

  • Connection: Certain poisons interrupt critical events in cellular respirationRotenoneCyanide, carbon monoxideOligomycin

  • Fermentation is an anaerobic alternative to aerobic respirationSome of your cells can actually work for short periods without oxygenFor example, muscle cells can produce ATP under anaerobic conditionsFermentationThe anaerobic harvest of food energy Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP

  • Aerobic metabolismWhen enough oxygen reaches cells to support energy needs Anaerobic metabolismWhen the demand for oxygen outstrips the bodys ability to deliver itAnaerobic metabolismWithout enough oxygen, muscle cells break down glucose to produce lactic acidLactic acid is associated with the burn associated with heavy exerciseIf too much lactic acid builds up, your muscles give out

  • Fermentation in Human Muscle CellsHuman muscle cells can make ATP with and without oxygenThey have enough ATP to support activities such as quick sprinting for about 5 secondsA secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 secondsTo keep running, your muscles must generate ATP by the anaerobic process of fermentation

  • Fermentation in MicroorganismsVarious types of microorganisms perform fermentationYeast cells carry out a slightly different type of fermentation pathwayThis pathway produces CO2 and ethyl alcoholThe food industry uses yeast to produce various food products

  • In alcoholic fermentation, pyruvic acid is converted to CO2 and ethanolThis recycles NAD+ to keep glycolysis working

  • In lactic acid fermentation, pyruvic acid is converted to lactic acidAs in alcoholic fermentation, NAD+ is recycledLactic acid fermentation is used to make cheese and yogurt

  • Cells use many kinds of organic molecules as fuel for cellular respirationPolysaccharides can be hydrolyzed to monosaccharides and then converted to glucose for glycolysisProteins can be digested to amino acids, which are chemically altered and then used in the Krebs cycleFats are broken up and fed into glycolysis and the Krebs cycleINTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS

  • Food molecules provide raw materials for biosynthesisIn addition to energy, cells need raw materials for growth and repairSome are obtained directly from foodOthers are made from intermediates in glycolysis and the Krebs cycleBiosynthesis consumes ATP

  • Biosynthesis of macromolecules from intermediates in cellular respiration

  • The fuel for respiration ultimately comes from photosynthesisAll organisms have the ability to harvest energy from organic moleculesPlants, but not animals, can also make these molecules from inorganic sources by the process of photosynthesis


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