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Thread: Cellular Resperation

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    FarmerDave's Avatar
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    Greetings! I am still a little unclear about the process of cellular resperation and i was wondering if someone could help me out with the basics. I would like some clearing up of the basics of glycolysis and the Krebs cycle, but mostly the Electron transport chain.

    That completely stumps me!

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    Stay chooned in for more! Clint's Avatar
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    I'm too tired and frustrated (no, not with you) to type it up myself so i'll just give you some URLS.

    Wikipedia

    Is your

    Friend

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    what class is this for? I'm guessing I could probably help you (I've already gone through genetics and cell). PM me with any specific questions and I'll try to clarify
    Z polski y dumny
    Prayer - how to do nothing and still think you're helping.
    http://www.youtube.com/watch?v=5F5aCUNE4Z8
    ^^^Newest vid

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    nepenthes_ak's Avatar
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    what does glucose and citric acid have to do with cellular respiration? Now I'm confused!

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    FarmerDave's Avatar
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    I would like it if someone explanined oxidative phosphorilation.

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    Nepenthes Specialist nepenthes gracilis's Avatar
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    For cellular respiration to take place all of those processes are required. Repiration (of plants) in a nutshell:
    IN the mitochondria, the plant is trying to perform an energy transfer. Glucose to ATP.

    1: Glycolysis - happens in the cytoplasm. glucose > 2 pyruvate + 2 ATP +2NADPH
    Transition reaction- Pyruvate > acetyl COA +NADH +C02
    2: TCA (Krebs) Cycle: Not explaining this part but when the Krebs cycle runs, it is ripping the carbon chain apart and releases energy and electrons

    3: Electron transport chain also refer to wikipedia lol.

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    nepenthes_ak's Avatar
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    Ohhh now I understand, that was the part of Biology I failed...



    but you know its all good

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    Tropical Fish Enthusiast jimscott's Avatar
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    Not the Krebs Cycle! That was one, nasty looking diagram of that whole operation!


    Phases of the Krebs Cycle


    After the glycolysis takes place in the cell's cytoplasm, the pyruvic acid molecules travel into the interior of the mitochondrion. Once the pyruvic acid is inside, carbon dioxide is enzymatically removed from each three-carbon pyruvic acid molecule to form acetic acid. The enzyme then combines the acetic acid with an enzyme, coenzyme A, to produce acetyl coenzyme A, also known as acetyl CoA.

    Once acetyl CoA is formed, the Krebs cycle begins. The cycle is split into eight steps, each of which will be explained below.

    Diagram of Krebs Cycle





    Step 1

    The acetic acid subunit of acetyl CoA is combined with oxaloacetate to form a molecule of citrate. The acetyl coenzyme A acts only as a transporter of acetic acid from one enzyme to another. After Step 1, the coenzyme is released by hydrolysis so that it may combine with another acetic acid molecule to begin the Krebs cycle again.

    Step 2

    The citric acid molecule undergoes an isomerization. A hydroxyl group and a hydrogen molecule are removed from the citrate structure in the form of water. The two carbons form a double bond until the water molecule is added back. Only now, the hydroxyl group and hydrogen molecule are reversed with respect to the original structure of the citrate molecule. Thus, isocitrate is formed.

    Step 3

    In this step, the isocitrate molecule is oxidized by a NAD molecule. The NAD molecule is reduced by the hydrogen atom and the hydroxyl group. The NAD binds with a hydrogen atom and carries off the other hydrogen atom leaving a carbonyl group. This structure is very unstable, so a molecule of CO2 is released creating alpha-ketoglutarate.

    Step 4

    In this step, our friend, coenzyme A, returns to oxidize the alpha-ketoglutarate molecule. A molecule of NAD is reduced again to form NADH and leaves with another hydrogen. This instability causes a carbonyl group to be released as carbon dioxide and a thioester bond is formed in its place between the former alpha-ketoglutarate and coenzyme A to create a molecule of succinyl-coenzyme A complex.

    Step 5

    A water molecule sheds its hydrogen atoms to coenzyme A. Then, a free-floating phosphate group displaces coenzyme A and forms a bond with the succinyl complex. The phosphate is then transferred to a molecule of GDP to produce an energy molecule of GTP. It leaves behind a molecule of succinate.

    Step 6

    In this step, succinate is oxidized by a molecule of FAD (Flavin adenine dinucleotide). The FAD removes two hydrogen atoms from the succinate and forces a double bond to form between the two carbon atoms, thus creating fumarate.

    Step 7

    An enzyme adds water to the fumarate molecule to form malate. The malate is created by adding one hydrogen atom to a carbon atom and then adding a hydroxyl group to a carbon next to a terminal carbonyl group.

    Step 8

    In this final step, the malate molecule is oxidized by a NAD molecule. The carbon that carried the hydroxyl group is now converted into a carbonyl group. The end product is oxaloacetate which can then combine with acetyl-coenzyme A and begin the Krebs cycle all over again.

    Summary

    In summary, three major events occur during the Krebs cycle. One GTP (guanosine triphosphate) is produced which eventually donates a phosphate group to ADP to form one ATP; three molecules of NAD are reduced; and one molecule of FAD is reduced. Although one molecule of GTP leads to the production of one ATP, the production of the reduced NAD and FAD are far more significant in the cell's energy-generating process. This is because NADH and FADH2 donate their electrons to an electron transport system that generates large amounts of energy by forming many molecules of ATP.

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