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  • You're facing a giant bowl

  • of energy packed Carbon Crunchies.

  • One spoonful. Two. Three.

  • Soon, you're powered up by the energy surge

  • that comes from your meal.

  • But how did that energy get into your bowl?

  • Energy exists in the form of sugars

  • made by the plant your cereal came from,

  • like wheat or corn.

  • As you can see, carbon is the chemical backbone,

  • and plants get their fix of it

  • in the form of carbon dioxide, CO2,

  • from the air that we all breath.

  • But how does a plant's energy factory,

  • housed in the stroma of the chloroplast,

  • turn a one carbon gas, like CO2,

  • into a six carbon solid, like glucose?

  • If you're thinking photosynthesis, you're right.

  • But photosynthesis is divided into two steps.

  • The first, which stores energy from the sun

  • in the form of adenosine triphosphate, or ATP.

  • And the second, the Calvin cycle, that captures carbon

  • and turns it into sugar.

  • This second phase represents one of nature's

  • most sustainable production lines.

  • And so with that, welcome to world's most miniscule factory.

  • The starting materials?

  • A mix of CO2 molecules from the air,

  • and preassembled molecules called

  • ribulose biphosphate, or RuBP,

  • each containing five carbons.

  • The initiator? An industrious enzyme named rubisco

  • that welds one carbon atom from a CO2 molecule

  • with the RuBP chain

  • to build an initial six carbon sequence.

  • That rapidly splits into two shorter chains

  • containing three carbons each

  • and called phosphoglycerates, or PGAs, for short.

  • Enter ATP, and another chemical called

  • nicotinamide adenine dinucleotide phosphate,

  • or just NADPH.

  • ATP, working like a lubricant, delivers energy,

  • while NADPH affixes one hydrogen to each of the PGA chains,

  • changing them into molecules called

  • glyceraldehyde 3 phosphates, or G3Ps.

  • Glucose needs six carbons to form,

  • made from two molecules of G3P,

  • which incidentally have six carbons between them.

  • So, sugar has just been manufactured, right?

  • Not quite.

  • The Calvin cycle works like a sustainable production line,

  • meaning that those original RuBPs

  • that kicked things off at the start,

  • need to be recreated by reusing materials

  • within the cycle now.

  • But each RuBP needs five carbons

  • and manufacturing glucose takes a whole six.

  • Something doesn't add up.

  • The answer lies in one phenomenal fact.

  • While we've been focusing on this single production line,

  • five others have been happening at the same time.

  • With six conveyor belts moving in unison,

  • there isn't just one carbon that gets soldered

  • to one RuBP chain,

  • but six carbons soldered to six RuBPs.

  • That creates 12 G3P chains instead of just two,

  • meaning that all together, 36 carbons exist:

  • the precise number needed to manufacture sugar,

  • and rebuild those RuBPs.

  • Of the 12 G3Ps pooled together,

  • two are siphoned off to form

  • that energy rich six carbon glucose chain.

  • The one fueling you via your breakfast. Success!

  • But back on the manufacturing line,

  • the byproducts of this sugar production

  • are swiftly assembled to recreate those six RuBPs.

  • That requires 30 carbons,

  • the exact number contained by the remaining 10 G3PS.

  • Now a molecular mix and match occurs.

  • Two of the G3Ps are welded together

  • forming a six carbon sequence.

  • By adding a third G3P, a nine carbon chain is built.

  • The first RuBP, made up of five carbons,

  • is cast from this,

  • leaving four carbons behind.

  • But there's no wastage here.

  • Those are soldered to a fourth G3P molecule,

  • making a seven carbon chain.

  • Added to a fifth G3P molecule,

  • a ten carbon chain is created,

  • enough now to craft two more RuBPs.

  • With three full RuBPs recreated

  • from five of the ten G3Ps,

  • simply duplicating this process

  • will renew the six RuBP chains

  • needed to restart the cycle again.

  • So the Calvin cycle generates the precise number

  • of elements and processes

  • required to keep this biochemical production line

  • turning endlessly.

  • And it's just one of the 100s of cycles

  • present in nature.

  • Why so many?

  • Because if biological production processes were linear,

  • they wouldn't be nearly as efficient or successful

  • at using energy to manufacture the materials

  • that nature relies upon, like sugar.

  • Cycles create vital feedback loops

  • that repeatedly reuse and rebuild ingredients

  • crafting as much as possible

  • out of the planet's available resources.

  • Such as that sugar,

  • built using raw sunlight and carbon

  • converted in plant factories

  • to become the energy that powers you

  • and keeps the cycles revolving in your own life.

You're facing a giant bowl

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B2 H-INT TED-Ed carbon energy chain production glucose

【TED-Ed】Nature's smallest factory: The Calvin cycle - Cathy Symington

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    VoiceTube   posted on 2014/06/03
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