A2 Biology - Calvin cycle: The light-independent stage (OCR A Chapter 17.3)

The Calvin cycle is the second stage of photosynthesis which does not require light.
1. Fixation
Carbon dioxide reacts with ribulose bisphosphate to make glycerate phosphate by the action of the enzyme Rubisco.
2. Reduction
Glycerate phosphate is converted into triose phosphate with the actions of ATP (providing energy for molecular rearrangement) and reduced NADP (donating a proton for the reduction).
3. Regeneration
Triose phosphate is converted into ribulose bisphosphate by the action of ATP.
Glycerate phosphate can branch off to make amino acids and fatty acids, which are then used to make proteins and lipids.
Triose phosphate can also be used to make glycerol (which combines with fatty acids made by GP to make lipids) and hexose sugars (eg. glucose), which can then go on to form starch and cellulose.
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[@BioRach]

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[@BioRach]

I'm glad you find them helpful! :D I'll try my best to make more soon, keep checking back :) Thanks for watching!

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[@jessicah2809]

I thought GP and TP were both 3-carbon molecules?

[@BioRach]

Yes you are correct. I should've make it clear in the video that it should be two GP and two TP made. At A-level, you wouldn't be asked to know the structures of them, so I simplified into the total number of carbons in each "section", but not the best thing. Thanks for watching and pointing that out! :)

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Literally the easiest explaination to this topic.

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Thank you so much! Had to teach myself this whole topic and this literally saved me

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Thank you very much.

[@BioRach]

Thanks for watching :D

[@adityaiyer801]

Wouldn't RuBP combine with CO2 to create an unstable 6 carbon intermediate, that breaks into 2 3 carbon Glycerate-3-phosphate molecules?

[@BioRach]

Yes you're right! It was my mistake in the video. Also TP is a 3C molecule in the same logic.

[@TheBullsBaller]

With the transition from TP to RuBP you said that when ATP was converted to ADP and Pi that the Pi remained, isn't it bonded with the TP to make RuBP (BIphosphate) therefore you should write ATP > ADP

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super helpful again thanks

[@BioRach]

Thank you for watching :D

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fascinating.

[@BioRach]

Haha it is an interesting topic. Thanks for watching! :)

[@gamingspotlight6194]

So would the first 3C phosphorylated sugar produced be GP or TP?

[@visamkhan8916]

The first 3C phosphorylated sugar will be TP. Gp is also a 3C molecule but its not a carbohydrate.

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i learn much from your video:)

[@BioRach]

Glad it helps you! :D

[@mohammadqasimawais9155]

Is this a revision or a regular class? Cause it took my teacher a month for this chapter.

[@BioRach]

It's mainly revision, though hopefully I've explained it in a way that it's easy enough to understand in the first few rounds. It is a complicated topic so taking more time to go through it will be beneficial! :)

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[@ravjayakodi2746]

what happens to the lost carbon going from TP to Rubp?

[@BioRach]

TP does not immediately turn into RuBP. It will stay stable until there are other TP molecules are made to react together to either make organic molecules (eg. Glucose), or regenerate RuBP.

[@BioRach]

So for example, two TP molecules can make one hexose sugar.
Once there are 5 TP molecules, then they'll react to make 3 RuBP molecules.

[@Charlotte-hf5jz]

how has TP been regenerated to form RuBP if it’s 3x2C and RuBP is 5C?

[@BioRach]

They will need 5 TP to be made in order to regenerate 1 RuBP.

[@Charlotte-hf5jz]

@@BioRach thank you so much for responding! do you mean 3 RuBP to balance the amount of carbons?

[@kayenatafzal8845]

where does this stage happen? in the thylakoid membrane like light dependant?

[@alexandra-uf5qg]

In the stroma

[@blackghost4823]

light independent whuch happens in the stroma but the process uses products NADPH and ATP from the light dependent reaction which happens at the thylakoid membrabe

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