The Mechanisms of Electron Transport: The Z Scheme

Original video: https://www.youtube.com/watch?v=d8pc912jUxE

Video Transcript:

You know about these antenna pigments right? How the energy is transferred? In what manner the energy or the electron is transferred? that movement of electron the moment it has activated the reaction center the p680 it will move in a special manner that manner we call it the Z scheme or if you America you call it Z scheme. But please don't say Z, because unds like “red neck”. You know red neck? Farmer, to show that you are low class life working on labor hard work.

That thing this that scheme, meaning that the electron how do you say this? Remember you have learned, there's a different way to say this different way to say this ground state reaction center P680 excited state reaction center P680. We start in here P680 let's see whether I can remember lesson from 12 years ago. But who's going to validate right? This will be excited to become excited P680, now this will be transferred to a series of electron carriers. You start with pheophytin, then you start with plastoquinone a, then you go to plastoquinone B, then you go to cytochrome b6f then you go to plastocyanin. Is that correct? Then you will meet with, what is this? Yes ground state p700 then you're going to go up to P700 star and then you will go to a not this is actually chlorophyll but we call it A0 then we go to A1 then you go to Iron sulfur X then you go to iron sulfur A, then you go to iron sulfur B then you go to ferredoxin then you go to flavoprotein ferredoxin NADP+ reductase then you go to NADP+.

Can you imagine I have not taught you this. Since I can remember, this I expect you to know remember this. by the way cytochrome b6f, it has its own structure which we'll see later but in essence, this is the Z scheme. Energy go up, then get it hits the excitation then it goes down has state of reaction going downhill. hence the word hill reaction named by Robert Hill then it goes, 680 nm to 700 nm, that's only 20 nm worth of energy difference. Then it will excite the second reaction center the ground state P700 then it gets excited then it will transfer to this cascade of reaction. , Fe means iron sulfur protein these are all protein all of these are protein. But bear in mind this one thing, not all of them is integral protein, me of them protein on the surface for example this thing plastocyanin here. Plastocyanin is this guy it's not it's not in the thylakoid membrane and this ferredoxin, FNR and NADP plus al in the stroma. They are not necessary in the integral membrane protein only four, for sure the one that you just now. Then get excited P700 pass down to chlorophyll, chlorophyll a, and A1 got a name. The name here is let me see can I remember that Wikipedia please. This phylloquinone, transfer to FeSx, FeSA, FeSB. Right, you will see in the form of plastoquinone a and plastoquinone b, that is simply the reduction state of it. If you learn chemistry, I give example for plastoquinone, plastoquinone it's got three states of it plastoquinone is oxidized state, then you have plastosemiquinone, the symbol becomes like this, because it only have one electron coming to it. But the moment it is filled with hydrogen it become plastoquinol or I think in the book, it's called this PQH2, plastydroquinone. This become PH2 this is only PQ, no charges receive one electron receive two hydrogen still similar molecule but now the molecule with different state of charges or reduction level attached to it. Since I already said plastydroquinone. This is why you got your H2O right, you got your H2O got split, you got I think two electron? Four hydrogens? Is it four hydrogen? Oxygen. This is where you got your oxygen two molecules of water is split because the moment it gets excited, this thing contains hole this hole needs to be filled in by mebody and who is that mebody? This thing steal electron from water and then water is oxidized, because water is oxidized, H2O is split. When it is split that's why you got oxygen that's plus 4 hydrogens.

Finally I just want to clarify on that H+. H means if you only H it means hydrogen one electron plus one proton. If it says hydride means hydrogen -, no proton. If it says proton, it means hydrogen +. Three levels of hydrogen we are talking about here are you talking about atomic hydrogen like in the case here or hydride of hydrogen H- or proton of hydrogen H+. The splitting of water producing H+ proton of hydrogen. The reduction of plastoquinone is with the addition of atomic hydrogen right. The hydride of hydrogen H- this will you later me not all molecules accept that .

Reference book: Plant Physiology and Development 7th Edition

by Lincoln Taiz, Ian Max Møller, Angus Murphy, Eduardo Zeiger

Full video: https://www.youtube.com/watch?v=dYs_TczAsM0

Attribution 4.0 International — CC BY 4.0 - Creative Commons