WEBVTT

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You're facing a giant bowl

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of energy packed Carbon Crunchies.

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One spoonful. Two. Three.

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Soon, you're powered up by the energy surge

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that comes from your meal.

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But how did that energy get into your bowl?

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Energy exists in the form of sugars

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made by the plant your cereal came from,

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like wheat or corn.

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As you can see, carbon is the chemical backbone,

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and plants get their fix of it

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in the form of carbon dioxide, CO2,

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from the air that we all breath.

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But how does a plant's energy factory,

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housed in the stroma of the chloroplast,

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turn a one carbon gas, like CO2,

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into a six carbon solid, like glucose?

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

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But photosynthesis is divided into two steps.

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The first, which stores energy from the sun

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in the form of adenosine triphosphate, or ATP.

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And the second, the Calvin cycle, that captures carbon

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and turns it into sugar.

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This second phase represents one of nature's

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most sustainable production lines.

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

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The starting materials?

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A mix of CO2 molecules from the air,

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and preassembled molecules called

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ribulose biphosphate, or RuBP,

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each containing five carbons.

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The initiator? An industrious enzyme named rubisco

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that welds one carbon atom from a CO2 molecule

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with the RuBP chain

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to build an initial six carbon sequence.

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That rapidly splits into two shorter chains

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containing three carbons each

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and called phosphoglycerates, or PGAs, for short.

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Enter ATP, and another chemical called

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nicotinamide adenine dinucleotide phosphate,

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or just NADPH.

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ATP, working like a lubricant, delivers energy,

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

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changing them into molecules called

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glyceraldehyde 3 phosphates, or G3Ps.

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Glucose needs six carbons to form,

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made from two molecules of G3P,

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which incidentally have six carbons between them.

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So, sugar has just been manufactured, right?

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Not quite.

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The Calvin cycle works like a sustainable production line,

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meaning that those original RuBPs

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that kicked things off at the start,

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need to be recreated by reusing materials

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within the cycle now.

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But each RuBP needs five carbons

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and manufacturing glucose takes a whole six.

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Something doesn't add up.

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The answer lies in one phenomenal fact.

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

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five others have been happening at the same time.

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With six conveyor belts moving in unison,

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there isn't just one carbon that gets soldered

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to one RuBP chain,

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but six carbons soldered to six RuBPs.

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That creates 12 G3P chains instead of just two,

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meaning that all together, 36 carbons exist:

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the precise number needed to manufacture sugar,

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and rebuild those RuBPs.

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Of the 12 G3Ps pooled together,

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two are siphoned off to form

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that energy rich six carbon glucose chain.

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The one fueling you via your breakfast. Success!

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But back on the manufacturing line,

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the byproducts of this sugar production

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are swiftly assembled to recreate those six RuBPs.

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That requires 30 carbons,

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the exact number contained by the remaining 10 G3PS.

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Now a molecular mix and match occurs.

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Two of the G3Ps are welded together

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forming a six carbon sequence.

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

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The first RuBP, made up of five carbons,

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is cast from this,

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leaving four carbons behind.

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But there's no wastage here.

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Those are soldered to a fourth G3P molecule,

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making a seven carbon chain.

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Added to a fifth G3P molecule,

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a ten carbon chain is created,

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enough now to craft two more RuBPs.

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With three full RuBPs recreated

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from five of the ten G3Ps,

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simply duplicating this process

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will renew the six RuBP chains

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needed to restart the cycle again.

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So the Calvin cycle generates the precise number

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of elements and processes

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required to keep this biochemical production line

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turning endlessly.

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

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present in nature.

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Why so many?

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Because if biological production processes were linear,

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they wouldn't be nearly as efficient or successful

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at using energy to manufacture the materials

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that nature relies upon, like sugar.

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Cycles create vital feedback loops

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that repeatedly reuse and rebuild ingredients

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crafting as much as possible

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out of the planet's available resources.

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Such as that sugar,

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built using raw sunlight and carbon

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converted in plant factories

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to become the energy that powers you

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and keeps the cycles revolving in your own life.