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A2 Biology

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    Big test tomorrow, and I need a way to remember all the details of glycolysis/oxidative phosphorylation/krebs cycle/link reaction. Anyone got any smart ideas? It's making my head hurt!
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    (Original post by Ellie4)
    Big test tomorrow, and I need a way to remember all the details of glycolysis/oxidative phosphorylation/krebs cycle/link reaction. Anyone got any smart ideas? It's making my head hurt!
    You could try drawing a diagram and condense all the information onto that, although it might be a bit difficult, it should be easy to remember. I don't have fantastic revision techniques but diagrams do help to picture whats going on.
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    (Original post by Ramaya)
    You could try drawing a diagram and condense all the information onto that, although it might be a bit difficult, it should be easy to remember. I don't have fantastic revision techniques but diagrams do help to picture whats going on.
    Ok, I'll try to do something pretty with coloured pens! You're with edexcel aren't you? Any idea how much detail we need to know?
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    (Original post by Ellie4)
    Ok, I'll try to do something pretty with coloured pens! You're with edexcel aren't you? Any idea how much detail we need to know?
    Ah coloured pens - the basis of my learning. Important things are always in a colour! Yep I am with Edexcel. As for detail I think we need to know the key stages, not every little reation. I'm not sure if you use the NAS book but the compressed diagram would be sufficient. I havn't seen exam questions that ask for extreme detail, but enough to understand and explain whats happening and whats being produced. Sorry if that was a little confusing
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    (Original post by Ramaya)
    Ah coloured pens - the basis of my learning. Important things are always in a colour! Yep I am with Edexcel. As for detail I think we need to know the key stages, not every little reation. I'm not sure if you use the NAS book but the compressed diagram would be sufficient. I havn't seen exam questions that ask for extreme detail, but enough to understand and explain whats happening and whats being produced. Sorry if that was a little confusing
    Okey dokey, I'll see what I can do!
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    Electron / hydrogen carriers
    Many of the reactions in the stages of respiration involve oxidation by the removal of electrons or hydrogen atoms (H). These are transferred to electron/hydrogen carriers. Ultimately they are passed to oxygen to form water right at the very last stage of respiration.

    Two important electron/hydrogen carriers are NAD (nicotinamide adenine dinucleotide), and FAD (flavin adenine dinucleotide).



    Oxidation / Reduction
    Oxidation is the addition of oxygen, the removal of hydrogen or the loss of electrons.

    Reduction is the addition of hydrogen, the removal of oxygen or the gain of electrons.

    A quick way to remember this is "OILRIG":

    Oxidation Is Loss, Reduction Is Gain.



    Krebs Cycle
    This is also known as the citric acid cycle or the tricarboxylic acid cycle.

    For each glucose molecule, there were 2 pyruvic acid molecules formed, (and therefore 2 acetylCoA molecules formed) so the whole cycle takes place twice for every glucose molecule respired.



    Electron Transport Chain / Oxidative Phosphorylation
    Production of ATP using NADH and FADH
    So far we have in total, from one glucose molecule...

    6CO2s
    4 ATPs made directly
    10 reduced NADs
    2 reduced FADs

    Now all the hydrogen from the reduced hydrogen carriers enters a chain of reactions, which ultimately yields energy in the form of ATP.

    This theory about how the ATP is actually made is called the chemiosmotic theory. Oxygen acts as the final electron acceptor in the chain, so the oxygen, electrons and hydrogen ions together form water.

    Glycolysis

    1.
    Glucose is phosphorylated twice to make a 6C sugar phosphate. 2 ATPs are used to supply the P groups. This makes the glucose more reactive and so…

    2.
    The 6C sugar phosphate breaks down to form 2, 3-carbon sugar phosphates, called triose phosphates (TP).

    3.
    Hydrogen is removed from each of the 2 TP molecules. The hydrogens are passed to 2 NADs (the NADs are reduced). 2 ATPs are made directly from the conversion of each TP to pyruvic acid (written shorthand as PA or called pyruvate) as the phosphate groups are removed.

    This stage occurres in the cytoplasm. The next stage occurs in the mitochondria. From here, the reaction will only proceed if oxygen is available.

    The link reaction
    1.
    The PA molecules enter the mitochondrion.

    2.
    CO2 and hydrogen are removed from each PA to create 2 2-C molecules. The hydrogen is transferred to NAD

    3.
    The 2-C molecule is then combined with coenzyme A (CoA) to form the 2C compound, acetylCoA. (CoA is a vitamin derivative which acts as a transporter of the 'acetate' psrt left from the PA molecule)

    Krebs Cycle
    For each glucose molecule, there were 2 pyruvic acid molecules formed, (and therefore 2 acetylCoA molecules formed) so the whole cycle takes place twice for every glucose molecule respired.

    1.
    Each acetylCoA (2C) combines with an oxaloacetic acid (4C) to make a 6C compound (citric acid).

    2.
    In a series of steps, for each 6C compound,
    2 CO2 molecules are released,
    3 NAD molecules are reduced,
    2 FAD molecules are reduced,
    1 ATP molecule is made directly.

    3.
    The 4C compound is regenerated (by the removal of the 2 Cs in 2 CO2 molecules) so that the cycle can begin again with more molecules of acetylCoA.

    Electron Transport Chain / Oxidative Phosphorylation
    So far we have in total, from one glucose molecule...

    6CO2s
    4 ATPs made directly
    10 reduced NADs
    2 reduced FADs


    Now all the hydrogen from the reduced hydrogen carriers enters a chain of reactions, which ultimately yields energy in the form of ATP.

    Each hydrogen atom is split into its constituent H+ (hydrogen ion) and electron. The electron is the part that actually gets passed down the chain from carrier to carrier. The H+, however, remains in the mitochondrial matrix.

    The electron carriers are at successively lower energy levels hence, as the electron moves on from one carrier to the next some energy is released.

    This energy is used to pump H+ from the matrix into the space between the inner and outer mitochondrial membrane. The H+ concentration therefore increases, forming a concentration gradient.

    This means that the H+ ions have electrical potential energy. H+ then flows back down the gradient into the matrix through protein channels.

    Associated with each channel is an enzyme, ATP synthase. As the H+ ions flow through, their energy is used to make ATP.

    This theory about how the ATP is actually made is called the chemiosmotic theory. Oxygen acts as the final electron acceptor in the chain, so the oxygen, electrons and hydrogen ions together form water.
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    Mmm I knwo all that, I was just looking for a nice way to learn it!
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    if your with edexcel you need to know the above notes. is this a unit test? unit 4 respiration? coz i have done this test!
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    (Original post by G_S)
    if your with edexcel you need to know the above notes. is this a unit test? unit 4 respiration? coz i have done this test!
    It's a test on the whole of unit 4. Ok, thanks for telling me what I need to know, any ideas on how to get all that info into my head though?
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    I guess the best way to learn is to draw the processes out and then label - key thing is to repeat and label all the tiny bits of information and you'll be fine.
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    naa thats were im crap! basically in our college they have exam pro which has all the biology exam papers. all recent!! we revise from there and the test they give us is exactly the same as the test papers in exam pro! so we all get high marks!!! :cool:
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    (Original post by G_S)
    naa thats were im crap! basically in our college they have exam pro which has all the biology exam papers. all recent!! we revise from there and the test they give us is exactly the same as the test papers in exam pro! so we all get high marks!!! :cool:
    Lol, you're do well come time of the exam then!
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    i think the idae of the diagram really works, cos that way ull understand whats happening and where. thats the best way to know u know it, if u understand it.

    like in the krebs cycle, losing one carbon from a 5c leaves a 4c molecule, where does the carbon go - carbondioxide in respiration.

    it all links and ull see it when its all down on one page
Updated: November 3, 2004
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