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Edexcel 6BIO5 ~ 20h June 2014 ~ A2 Biology watch

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    Hi

    can someone summarise the respiration cycle please? I understand glycolysis/links/krebs but not the ETC/Chemiosmosis

    Have no idea what oxidative phosphorylation is either? Is it part of chemiosmosis?
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    I don't understand how oxygen is needed for the kreb cycle? Please help me 😭


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    (Original post by AnishaJayne)
    I don't understand how oxygen is needed for the kreb cycle? Please help me 😭


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    It's not? Oxygen is the final electron acceptor and is only involved in the electron transport chain. A part of oxidative phosphorylation.


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    (Original post by leafy9)
    It's not? Oxygen is the final electron acceptor and is only involved in the electron transport chain. A part of oxidative phosphorylation.


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    So why is the kreb cycle not involved in anaerobic respiration also then?

    Is it to do with the fact the oxygen frees up the NAD and FAD in oxidative phosphorylation to be used in the kreb cycle? < if thats correct (which i don't think is) then how can NAD be reduced in glycolysis and still be anaerobic?

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    (Original post by AnishaJayne)
    So why is the kreb cycle not involved in anaerobic respiration also then?

    Is it to do with the fact the oxygen frees up the NAD and FAD in oxidative phosphorylation to be used in the kreb cycle? < if thats correct (which i don't think is) then how can NAD be reduced in glycolysis and still be anaerobic?

    I asked my teacher this and she said 'stop over complicating it and just accept it'. I don't like accepting things so I would like to know this too :')

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    (Original post by LibbyG)
    I asked my teacher this and she said 'stop over complicating it and just accept it'. I don't like accepting things so I would like to know this too :')

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    Im so confused on how krebs need the NAD for the same concept that glycolysis does yet ones anaerobic and ones aerobic so silly!

    Also, I was kind of hoping by understanding this it would help with 5ci on january 2011 as I haven't a clue how they came up with that answer on the mark scheme!
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    (Original post by jooh_23)
    Hi

    can someone summarise the respiration cycle please? I understand glycolysis/links/krebs but not the ETC/Chemiosmosis

    Have no idea what oxidative phosphorylation is either? Is it part of chemiosmosis?
    Oxidative phosphorylation is what happens in ETC, its another name for ETC.

    ETC is where the H+ and e- from the glycolysis and link reactions and Krebs cycle is passed on through the chain of electron carriers and it undergoes a series of redox reactions, before reaching the final electron acceptor, which is O2. The overall reaction is O2 + 4H+ + 4e- -> 2H2O

    Chemiosmosis is another part of ETC, where the H+ pumped out of the matrix, into the intermembrane space, down the steep electrochemical gradient and it then diffuses back into the matrix through a channel protein ATPase, which produces ATP.
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    (Original post by LibbyG)
    I asked my teacher this and she said 'stop over complicating it and just accept it'. I don't like accepting things so I would like to know this too :')

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    (Original post by AnishaJayne)
    Im so confused on how krebs need the NAD for the same concept that glycolysis does yet ones anaerobic and ones aerobic so silly!

    Also, I was kind of hoping by understanding this it would help with 5ci on january 2011 as I haven't a clue how they came up with that answer on the mark scheme!

    Glycolysis is the only stage in anaerobic respiration.

    Basically, remember that NAD is reduces by 2H during glycolysis. Pyruvate is also formed. The formed NADH reduces the pyruvate into lactate. When oxygen is available, the lactate gets oxidised back into pyruvate and can go through the rest of aerobic respiration.

    The ATP produced by glycolysis is the only source of energy during anaerobic respiration
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    (Original post by mynameisntbobk)
    Glycolysis is the only stage in anaerobic respiration.

    Basically, remember that NAD is reduces by 2H during glycolysis. Pyruvate is also formed. The formed NADH reduces the pyruvate into lactate. When oxygen is available, the lactate gets oxidised back into pyruvate and can go through the rest of aerobic respiration.

    The ATP produced by glycolysis is the only source of energy during anaerobic respiration
    Yep, thank you. I think their question was why does the Krebs cycle not happen in anaerobic respiration if it doesn't need oxygen?
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    (Original post by letsbehonest)
    Yep, thank you. I think their question was why does the Krebs cycle not happen in anaerobic respiration if it doesn't need oxygen?

    Oh lol. I'm assuming its because Krebs takes place in the matrix of mitochondria, and so transporting pyruvate there wastes time & energy and there's no real benefit of it. Plus it makes it easier to just transport ATP produced to where its needed
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    The Krebs Cycle does need oxygen doesn't it? When the carbon dioxide is produced I thought that came from oxygen, not from the sugar. I always thought that was why the Link Reaction couldn't occur in anaerobic conditions- carbon dioxide is usually a product, but it can't be made because there's no oxygen.

    Confused!


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    (Original post by mynameisntbobk)
    Oh lol. I'm assuming its because Krebs takes place in the matrix of mitochondria, and so transporting pyruvate there wastes time & energy and there's no real benefit of it. Plus it makes it easier to just transport ATP produced to where its needed
    Thanks! That makes sense

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    (Original post by StephenNaulls)
    The Krebs Cycle does need oxygen doesn't it? When the carbon dioxide is produced I thought that came from oxygen, not from the sugar. I always thought that was why the Link Reaction couldn't occur in anaerobic conditions- carbon dioxide is usually a product, but it can't be made because there's no oxygen.

    Confused!


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    I'm pretty sure it doesn't. I thought the oxygen was already present in pyruvate/acetyl CoA

    Edit: basically no oxygen = no final electron acceptor in ETC = no deprotination/oxidation of NADH = less NAD available to accept protons in the Krebs cycle = Krebs cycle eventually halts

    (Original post by LibbyG)
    Thanks! That makes sense

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    No problem hope its right though, not 100% sure
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    (Original post by mynameisntbobk)
    Oh lol. I'm assuming its because Krebs takes place in the matrix of mitochondria, and so transporting pyruvate there wastes time & energy and there's no real benefit of it. Plus it makes it easier to just transport ATP produced to where its needed
    Pyruvate does go to the mitochondria membrane for link?


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    (Original post by AnishaJayne)
    Pyruvate does go to the mitochondria membrane for link?


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    In anaerobic, pyruvate gets converted into lactate
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    If possible, can somebody type out the whole respiration cycle thing with mark scheme type points.. we will all benefit and I'll be especially thankful!!
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    (Original post by mynameisntbobk)
    I'm pretty sure it doesn't. I thought the oxygen was already present in pyruvate/acetyl CoA

    Edit: basically no oxygen = no final electron acceptor in ETC = no deprotination/oxidation of NADH = less NAD available to accept protons in the Krebs cycle = Krebs cycle eventually halts




    No problem hope its right though, not 100% sure
    But then I don't understand why LR/Krebs aren't involved in anaerobic, it makes no sense

    Also, I just read this, which summarises what I thought but in a better way (from wikianswers though, so questionable reliability )

    'Glycolysis produces pyruvate as an end product, but if this is to enter the krebs cycle, it has to be OXIDATIVELY decarboxylated to acetyl CoA (Link Reaction) and this obviously cannot happen if theres no oxygen. So there is an accumulation of pyruvate, which is isomerised to lactate by lactate dehydrogenase so that it can be exported out of the cell'
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    (Original post by StephenNaulls)
    But then I don't understand why LR/Krebs aren't involved in anaerobic, it makes no sense

    Also, I just read this, which summarises what I thought but in a better way (from wikianswers though, so questionable reliability )

    'Glycolysis produces pyruvate as an end product, but if this is to enter the krebs cycle, it has to be OXIDATIVELY decarboxylated to acetyl CoA (Link Reaction) and this obviously cannot happen if theres no oxygen. So there is an accumulation of pyruvate, which is isomerised to lactate by lactate dehydrogenase so that it can be exported out of the cell'

    I read this on yahoo answers "The lack of oxygen does indeed halt the kreb cycle but not directly.

    The lack of the terminal electron acceptor (oxygen) in the electron transport chain leads to the inability for NADH to be deprotonated to NAD+. The eventual lack of NAD+ ceases the Krebs Cycle." I dunno I kind of agree with this explanation more (mainly because I was taught something like it).

    I really don't know, because oxidative decarboxylation is mention on Wikipedia where it talks about it occurring in the citric cycle (Krebs). But I always though lactate was produced to make NAD available to carry on with glycolysis (pyruvate isn't an isomer of lactate is it?)
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    (Original post by mynameisntbobk)
    I read this on yahoo answers "The lack of oxygen does indeed halt the kreb cycle but not directly.

    The lack of the terminal electron acceptor (oxygen) in the electron transport chain leads to the inability for NADH to be deprotonated to NAD+. The eventual lack of NAD+ ceases the Krebs Cycle." I dunno I kind of agree with this explanation more (mainly because I was taught something like it).

    I really don't know, because oxidative decarboxylation is mention on Wikipedia where it talks about it occurring in the citric cycle (Krebs). But I always though lactate was produced to make NAD available to carry on with glycolysis (pyruvate isn't an isomer of lactate is it?)
    Umm, I don't think so. To make lactate NADH is oxidised to reduce pyruvate, because pyruvate has extra hydrogen atoms (i think that's why the enzyme that breaks it down is lactate dehydrogenase).

    Maybe they're both right? Lack of oxygen means oxidative decarboxylation can't occur, but the lack of oxygen as a terminal electron acceptor also means lack of NAD+, which means Krebs is completely halted...? Bloody hate Biochemistry haha!
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    (Original post by StephenNaulls)
    Umm, I don't think so. To make lactate NADH is oxidised to reduce pyruvate, because pyruvate has extra hydrogen atoms (i think that's why the enzyme that breaks it down is lactate dehydrogenase).

    Maybe they're both right? Lack of oxygen means oxidative decarboxylation can't occur, but the lack of oxygen as a terminal electron acceptor also means lack of NAD+, which means Krebs is completely halted...? Bloody hate Biochemistry haha!
    If there is lack of NAD+ even glycolysis cannot occur as it needs NAD

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