Photosynthesis
Photosynthesis : part A - The Light Reactions
\r\nAmusical Lecture by Glenn Wolkenfeld
\r\n
\r\nA music Lecture by Glenn Wolkenfeld
\r\nBoys and girls tell me what you think of this,
\r\nTime for a lesson ‘bout photosynthesis
\r\nCells use light to combine water carbon dioxide.
\r\nGonna see electrons going for a wild ride.
\r\nMaking sugar, making sweet O¬2.
\r\nBut why should photosynthesis matter to you?
\r\nFood on your table.
\r\nO2 rich atmosphere.
\r\nWithout photosynthesis you simple wouldn’d be here.
\r\n
\r\n( Part I, The Big Picture)
\r\nPhotosynthesis is a redox reaction.
\r\nPowered by light using enzymatic action.
\r\nWater’s oxidized, CO2’s re duced
\r\nThe sugar that results you drink in orange juice.
\r\nThe overall reaction has two phases.
\r\nFirst is the light reactions which has as its basis.
\r\nLight powered production of ATP.
\r\nO2 is the by – product and you will see.
\r\nProduction of electron carrier NADPH
\r\nWhich provides reducing power needed in the second phase
\r\n‘Cause NADPH, during phase 2
\r\nProvides what’s needed for reducing CO2
\r\nNADPH ia made by a reduction of NADP+, whose function
\r\nIs to absorb electrons and pick up H,
\r\nGaining energy and making NADPH.
\r\nPhase 2 is the Calvin Cycle makes carbohydrate,
\r\nLike sugar and starches and fibers on your lunch plate.
\r\nIt’s how plants make food animals eat.
\r\nPhotosynthesis, it’s so sweet!
\r\n
\r\n(Part II: Chloroplasts, Thylakoids, Light, and Chlorophyll)
\r\nIn a lesf there’s mesophyllic tissue
\r\nAnd cells with chloroplasts key to the issue.
\r\nChloroplasts are almost like cells in every way,
\r\nWith their own ribosomes and their own DNA.
\r\nThey even reproduce themselves, splitting into half.
\r\nA clue for this organelle’s independent past.
\r\nThis theory has a name endosymbiosis,
\r\nDeveloped in the 60s by Lynn Margulis.
\r\nInside the chloroplast is the fluid stroma.
\r\nIt’s true in Tokyo.
\r\nIt’s true in Roma.
\r\nStroma syrrounds little thylakoids.
\r\nEach one has a hollow space inside.
\r\nThe thylakoid’s membrane is loaded with protein.
\r\n‘Cause it’s the light reactions’ scene.
\r\nIt’s all about using light for powering electrons,
\r\nAll about grabbing the power in photons.
\r\nThe photons needed are are those from light,
\r\nWhich has the energy to make the world bright.
\r\nThe highest frequency that we can see,
\r\nIs violet light with wavelength 380.
\r\n380 nanometers, sounds small,
\r\nBut next to gamma rays it’s rather tall.
\r\nRed light shines at 750.
\r\nIsn’t the visible spectrum nifty?
\r\nPhotons are packets of light energy,
\r\nBoth a wave and a particle, you see.
\r\nPhootins get adsorbed by pigments.
\r\nIt’s real, it’s true, it ain’t no figment!
\r\nMost important are green chlorophylls.
\r\nOrange carotenoids, and yellow xanthophylls.
\r\nTogether they absorb light, mostly red and blue.
\r\nThe green is not absorbed it reflects back to you.
\r\nIn chlorophyll see the porphyrin ring.
\r\nSee the magnesium, which makes you want to sing,
\r\nMagnesium, metal with valence two.
\r\nYou’ll see those electrons rocketing through.
\r\nNotice the tail, a hydrocarbon chain.
\r\nWhich anchors chlorophyll into the thylakoid membrane.
\r\nA molecule with style, so pretty,
\r\nIn the thylakoid it makes electricity!
\r\n
\r\n( Part III)
\r\nEnglemann showed us the action spectrum.
\r\nUsed a prism to break the sun’s
\r\nLight into its frequencies.
\r\nShone it on spirogyra, filamentous algae.
\r\nThe O2 algae make will stimulate bacteria.
\r\nWhich will grow in any oxygen – rich area.
\r\nBacteria loved it over blue and red,
\r\nBut hardly grew over green, they might as well be dead!
\r\nThe line of growth is a refection, of photosynthesis’ action spectrum.
\r\nNote this won’t match, exactly,
\r\nThe absorption spectra of chlorophyll a or b.
\r\n‘Cause the cartenoids and xanthophylls we’ve met,
\r\nAbsorb light frequencies the chlorophylls can’t get.
\r\nAnd in the thylakoid they all cooperate,
\r\nIn using light to synthesize carbohydrate.
\r\nConsider chlorophyll in isolation,
\r\nShine some light upon it (call it photoexcitation)
\r\nThe valence electrons in magnessium
\r\nJump to an excited state, it’s so fun!
\r\nBut once up at that level, they can only fall.
\r\nBack to where they started, like a bouncing ball.
\r\nThese falling alectrons, release energy,
\r\nFluorescing as red light, as you can see.
\r\nBut in thylakoids, chlorophyll’s not alone,
\r\nInstesd a photosystem is chlorophyll’s home.
\r\nThe photosystem’s parts can take photons,
\r\nAnd use their energy to move electrons.
\r\nThe system’s antenna complex does the first capture,
\r\nChanging photon anergy into electron rapture.
\r\nThe energized electrons bounce like a ball,
\r\nAt the reaction center, they jump but do not fall.
\r\nA primary electron acceotor grabs them from on top,
\r\nAnd yanks them with a force reaction center cannot stop.
\r\nTo this oxidized reaction center we’ll return,
\r\nBut the details of electron flow it now is time to learn.
\r\n
\r\n( Part IV) ATP Synthesis in Non – Cyclic Electron Flow.
\r\nNon - cycle flow is the main pathway.
\r\nMuch confustion relates to the way
\r\nHootoystm II precedes photosystem I.
\r\nIt’s a fct to memorize, just get it done!
\r\nPS II’s antenna captures a photon,
\r\nGenerates a flow of electrons.
\r\nAll around the world, even n Haiti,
\r\nThey flow to reaction center P680.
\r\nThere electrons do not hover,
\r\nElectron acceptor passes them over.
\r\nTo the electron transport chain,
\r\nIn the thylakoid membrane.
\r\nThis chain’s like a bucket brigade.
\r\nEach molecule has a similar trade.
\r\nThey take energized electrons,
\r\nAnd use their energy for pumping protons.
\r\nFrom stroma to the thylakoid space.
\r\nPacking protons into that place.
\r\nThis makes a gradient across the thylkoid membrane
\r\nThe protons want “out” or they’ll go insane.
\r\nBut the protons can’t permeate.
\r\nThe membrane won’t allow escape.
\r\nThere’s only one port through which they travel.
\r\nIt’s the ATP Synthase channel.
\r\nThe “-ase” tells you this is an enzyme.
\r\nWhich makes ATP all the time.
\r\nIt has binding sites for ADP and Pi,
\r\nAnd channels for diffusing protons whose knetic energy.
\r\nChanges the binding sites’ conformation.
\r\nFusing ADP with Pi which for your information.
\r\nIs how thylakoids make ATP.
\r\nLife’s key form of energy.
\r\nFrom respiration this might feel familiar.
\r\nATP is made this way in mitochondria.
\r\nChemiosomosis is the name
\r\nATP production is the game.
\r\n
\r\n( Part V: NADPH Synthesis in Non – Cyclic Elecron Flow)
\r\nBack to our electons moved by the sun.
\r\nFlowing from Photosystem II to System I.
\r\nThey get to PS I lke a used up battery.
\r\nThe transport chain used up their energy.
\r\nBut when light hits PS I’s antenna
\r\nElectrons boune to reaction center.
\r\nThis one’s P700,
\r\nThat wavelength makes electrons go!
\r\nPS T’s electron acceptor grabs them away,
\r\nLeaving P700 in an oxidized way.
\r\nAnd P700 with its oxidized blues accepts the alectrons from PS II.
\r\nBak to electron from PS I.
\r\nIt now gose for a ride, having its own fun.
\r\nBut powering proton pumps ain’t its fate.
\r\nIt travels to NADP+ reductase.
\r\nAn enzyme plant cells count upon.
\r\nTo pass some H and electrons.
\r\nTo NADP+ which gets reduced.
\r\nIt’s how NADPH get produced.
\r\n
\r\n(Part VI: Oxygen Production in Non – Cycli Electron Flow)
\r\nThe by – product of these light reactions
\r\nIs oxygen here’s how it happens.
\r\nBack PS II, it came to arise,
\r\nThat P680 got oxidized
\r\nTo replace lost electrons P680 liberates.
\r\nElectrons from water which dissociates.
\r\nInto one oxygen and protons two,
\r\nThe single O will meet anoher forming O2.
\r\nThese protons are formed in the thylakoid space.
\r\nIncreasing proton concentration in that place.
\r\nSo we see a side effect of water’s oxidation.
\r\nIs enhancement of ATP creation.
Author by: TiengAnhHoc.com
