Biology - An Illustrated Guide to Science (794127), страница 6
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Tube-like strandsconnecting thylakoids from granum togranum are called stroma lamellae.● Chlorophyll and other pigments thatinitiate photosynthesis are found onthe outer layer of the thylakoids.● The light-dependent reaction takesplace in the thylakoids.●starch grainstromadetail of granumDetail of granumthylakoidStromagranumstromastroma lamellaInside the inner membrane is acomplex mix of enzymes and watercalled stroma. It is the site of the lightindependent reaction.© Diagram Visual Information Ltd.●32Chemistry ofphotosynthesisUNITYKey wordsglucoselight-dependentreactionlight-independentreactionNADPNADPHphotosynthesisLight-dependentreaction (photolysis)Light-independent reaction(carbon fixation)NADPH21Two linkedpathwaysPhotosynthesis is amultistepped processconsisting of two linkedreaction pathways—thelight-dependent reaction(LDR) and the lightindependent reaction(LIR).● Photosynthesis is usuallyshown as creating glucose,but this is also the startingpoint for a range of otherpathways.
Much of thesugar produced will beconverted to starch forstorage or be respired toproduce energy to driveother reactions.3STARCH,CELLULOSE●ATPNADP 2e–ATPThis reaction uses energyfrom the LDR to buildsugars.● Carbon dioxide isabsorbed by the plant andreduced to form sugar.● Some of the intermediateproducts of the reactioncan be shunted into otherreaction pathways to buildfats and even proteins.© Diagram Visual Information Ltd.●2ATP1GLYCEROLADP2433ADPATP3LIPIDSNADPH2Photosystem I●Light-independentreaction12Light-dependentreactionThis reaction produceschemicals (ATP andNADPH) that containenergy in a form that canbe used by the LIR.● The outputs are shown aselectrons (e-), which arecarried by chemicals thatlink them to the LIR.
Themain carrier is thecoenzyme NADP.ADPGLUCOSEADPNADP2H+Photosystem II2e–FATTY ACIDSACETYLCOENZYME APROTEINSAMINO ACIDSH2O12O21 Electron acceptor2 ATP formation from ADP bychemiosmotic mechanism3 Electron carrier chainflow of electrons in non-cyclicphotophosphorylationflow of electrons in cyclicphotophosphorylationsunlight energypassage of protons to NADPother chemical reactions1234Carbon dioxideRibulose diphosphatePhosphoglyceric acidPhosphoglyceraldehydereactions of Calvin cyclecarbohydrate synthesislipid synthesisprotein synthesisother chemical reactions33Summary of aerobicrespirationKey wordsadenosinetriphosphateaerobicrespirationelectrontransfer chainAerobic respiration1glycolysis (cytoplasm)glycolysis(cytoplasm)14Fuel-oxygen systems2● Living2ATP38ATPinnermembrane234ATP4oxidativephosphorylation53● GlucoseH2OoxidativephosphorylationKrebs cycle(mitochondrion)12O22ATPelectroncarrier chain(mitochondrion)4123463GlucosePyruvic acidOxygenCarbon dioxideWaterEnergy (ATP)Simple equation for aerobic respirationC6H12O6 + 6O26CO2 + 6H2O + energy (38 ATP)releases far too muchenergy for living things if itreacts with oxygen all at once,as happens in combustion.The respiration system allowsthe sugar to react in a series ofsmall steps that release smalleramounts of energy.
Theseenergy packets are collectedby a chemical called adenosinetriphosphate (ATP).● ATP passes these packets ofenergy onto other reactions inthe cell. ATP is sometimescalled the “energy currency” ofthe cell.Three step processGlucosePyruvic acidAcetyl coenzyme ACarbon dioxideglycolysis/Krebs cycle reactions123456things use a fuel–oxygensystem to manage energy.Energy is released when thefuel and the oxygen react, andis transferred to otherchemical systems that pass iton to other reactions in a cell.● The energy release andmanagement system in livingthings is called respiration.
Ifoxygen is involved, it is knownas aerobic respiration.The “energycurrency”mitochondrionKrebscycleglycolysisKrebs cyclerespirationATP produced by substrate-levelphosphorylationATP produced by oxidativephosphorylationhydrogen transferred by acceptorto electron carrier chainreduction of oxygen to water● Aerobicrespiration has threemain components: glycolysis,the Krebs cycle, and theelectron transfer chain (ETC).Glycolysis occurs in thecytoplasm and splits glucoseinto a smaller molecule.
Thispasses into the mitochondria,where it is further brokendown during the Krebs cycle,releasing carbon dioxide andhigh-energy electrons. TheETC then harvests the energyin these electrons.© Diagram Visual Information Ltd.MitochondrianUNITY34UNITYKey wordsadenosinetriphosphatecristaeKrebs cyclematrixmitochondrionribosomeMitochondrion: structureMitochondrion(part sectioned)outer membraneinner membraneSize and distributionMitochondria are present in all cellswith a nucleus.
The moremetabolically active a cell, the moremitochondria they are likely to have.● Mitochondria generally have a sausageshape, but some can be almostspherical. They are roughly the size ofbacteria, typically about half to aquarter as long as the cell nucleusdiameter.●cristamatrixCellDouble membranesLike chloroplasts, mitochondria have adouble membrane.
The outer one issmooth and separates the inside of themitochondria from the cytoplasm ofthe cell.● The inner membrane is folded inwardto produce many ridges called cristae.These project into the central space ofthe mitochondrion called the matrix.The infolding of the christae providesmore surface area for chemicalreactions to occur.● The matrix contains strands of DNA,ribosomes, or small granules.●mitochondrionMitochondrion: sectioncristaeEnzyme systemsintermembrane spaceinner membraneEnzymes floating freely in the matrixare concerned with the Krebs cycle—apart of the respiration pathway thatproduces excited electrons.● The cristae formed by the infoldedinner membrane contain enzymes thathandle the transfer of electrons fromthe Krebs cycle and produceadenosine triphosphate (ATP) througha series of complex reactions.© Diagram Visual Information Ltd.●outer membranematrix35ATP structureUNITYKey wordsATP structureadenosinetriphosphaterespirationSimplified structure1 Adenine2 Ribose3 PhosphateThe energy currency1Adenosine triphosphate (ATP) is amolecule that can collect and give outenergy when its phosphate groupsjoin or leave the adenosine molecule.You can think of the phosphate groupsas “rechargable batteries” or “energymoney”—they make other reactionsthat need energy happen.● When a phosphate group is releasedfrom ATP, the phosphate groupattaches itself to a molecule that needsenergy to take part in a reaction.
Theenergy in the phosphate groups“passes into” the other molecule, andthe reaction can take place.● Once the energy has beentransferred, the phosphategroup is released as lowenergy inorganic phosphate.This can then bereconnected to theadenosine molecule,provided energy is suppliedby respiration. In this waythe “battery” is “recharged.”●333adenosine diphosphate (ADP)adenosine triphosphate (ATP)Molecular structureNH2CadenineHNCCCNNCThe phosphate poolH● TheONCH2OCHHCHCCHOPOOH OHriboseadenosine diphosphate (ADP)adenosine triphosphate (ATP)OOPOOOPOHOphosphateenergy available toreactions in the celldepends on ATP, and if theconcentration of ATP falls,reactions will fail or slowdown. Since ATP can bereused many times, thisdoes not happen often.
Thelimiting factor is howquickly the ATP can berecycled from adenosinediphosphate (ADP) andinorganic phosphate.● The “phosphate pool” is thesupply of inorganicphosphate groups in the cellthat could be used to buildATP. If this pool “dried up,”then the cell would suffer alack of useful energy.© Diagram Visual Information Ltd.236UNITYKey wordsadenosinetriphosphateelectron transferchainKrebs cycleNADNADPElectron transfer chainProteolipid complexeshigh energy1 NAD2 Flavoprotein3 Coenzyme Q4 Cytochrome b5 Cytochrome c6 Cytochrome oxidaseKrebscycle2HEnergetic electronsThe Krebs cycle transfers energy intoelectrons that become “excited.”These electrons carry more energythan normal electrons.● Electrons are difficult to move aroundthe cell, so the cell uses hydrogenions, which have a positive charge andcan “drag” the negatively chargedelectrons along with them.● Compounds like nicotinamide adeninedinucleotide (NAD) and nicotinamideadenine dinucleotide phosphate(NADP) can bind to these hydrogenions (and so the electrons) to shuttlethem between the various parts of therespiration pathway and the start ofthe electron transfer chain.●1oxidizedenergyreduced2ATPADP + PiRedox reactionsoxidizedA chemical is oxidized when it gainsoxygen or loses an electron.
Acompound is reduced when it losesoxygen or gains an electron. Reductioninvolves losing oxygen or gaining anelectron.● Redox reactions usually involve thetransfer of energy between chemicals.●reduced34oxidizedreducedoxidizedenergyEnergy transfersHigh energy electrons are fed into theelectron transfer chain at one end andpass through a series of redoxreactions until they are linked withoxygen to make water (H20).Remember that although we talk ofelectrons moving, we are reallymoving hydrogen ions.● At various stages in this process,enough energy is released to buildadenosine triphosphate (ATP) fromadenosine diphosphate (ADP) andinorganic phosphate (Pi).reduced© Diagram Visual Information Ltd.●ATPADP + Pioxidized5reducedenergyreducedADP + Pi6oxidizedATPH2O12O2low energy37Anaerobic respirationUNITYKey wordsLactic acid fermentation in animalsaerobicrespirationanaerobicrespirationATP12ATPAnaerobic respiration2ADP2NAD4ADP4ATPNADH24C6H12O6(glucose)312342C3H6O3 + 2ATP(lactic acid) (energy)GlucoseFructose diphosphatePyruvic acidLactic acidAlcoholic fermentation in yeastAnaerobic respiration does notrequire oxygen to release energy fromsugar.
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