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Thread: Photosynthesis question.

  1. #1 Photosynthesis question. 
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    ok i am a very slow learner ( i forget most of everything i study within a day)

    and right know I am going over photosynthesis in preparation for the return of school days.

    So i would like to ask you ---> my fellow board members,can you help me understand photosynthesis?
    Here is what i think i know from reading my text book.
    1.sunlight is absorbed into Chlorophyll in the thylakoids.
    2.Chlorophyll transfer the energy to the reaction center (PS1)
    3.Electrons in reaction center jump to electron carriers and go through the electron transport system.
    4.Electrons from PS11 replace electrons lost from PS1
    5.H2O is broken down into hyydrogen ions, 4e-, and O2 from an enzyme to give PS11 electrons.
    6.electrons from PS11 reduce NAPD+ in PS1 and conver it into NAPDH
    7. active transport of protons across the thylakoid membrain transfers energy to an enzyme (ATP)
    8. The enzyme converts ATP into ADP and... i forgot
    9.and I am lost at the calvin cycle.


    I know I am stupid but thanks if you do post on my behalf.


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  3. #2  
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    2.Chlorophyll transfer the energy to the reaction center (PS1)
    3.Electrons in reaction center jump to electron carriers and go through the electron transport system.
    4.Electrons from PS11 replace electrons lost from PS1
    You've got some things mixed around here.

    1) Generally when one draws out photosynthesis, they start with PSII. Do not be confused by the labeling. The only reason PSI is called PSI is because it was discovered first. Otherwise, the starting point is more or less with PSII. The flow of electrons is from PSII to PSI and PSII is more abundant in the Chloroplast.

    2) PSI, when it absorbs light will kick out an electron, but this electron does not go into the electron transport system. The electrons from PSI are used to directly reduce NADP to NADPH.

    3) The electrons displaced from PSII enter the electron transport chain.

    So the overall scheme is that electrons from PSII enter the electron transport chain and then are transferred to PSI.

    This is known as the Z-Scheme. Google it just like that "Z-scheme" and you will likely find some nice images for the process of photosynthesis.

    6.electrons from PS11 reduce NAPD+ in PS1 and conver it into NAPDH
    Electrons from PSI reduce NADP+ to NADPH. The electrons that flow from PSII through the electron transport chain replace those electrons diplaced in PSI.

    7. active transport of protons across the thylakoid membrain transfers energy to an enzyme (ATP)
    1) Its not active transport of protons. The protons are moving down an electrochemical gradient, the movement of protons here is properly called facilitated diffusion.

    2) The enzyme's name is ATP synthase

    8. The enzyme converts ATP into ADP and... Crying or Very sad i forgot
    The enzyme (ATP synthase) converts ADP into ATP, you have it backwards.


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    Thank you
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  5. #4  
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    ok after going through a LOT of reading from different sources lets see if i have it. (from memory )

    1. Light is is absorbed by light absorbing pigments in PS11
    2. energy from the light goes to the reaction center.
    3. Enzymes take the electrons from H20 and splits it into Oxygen and H+
    4. Electrons go Through the electron transport system
    5. Protons and electrons help form ATP from ADP and pi adding a phosphate to ADP :? (not sure)
    6.electron has lost its energy from making ATP and is transported to PS1
    7.Light energy is transported to the reaction center where it re-energizes the electron.
    8. electron forms NADPH from NADP and H+
    9. and through many other reactions i have yet to even grasp, creates sugars.

    did i get it even close? its really confusing!! :x
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  6. #5  
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    2. energy from the light goes to the reaction center.
    3. Enzymes take the electrons from H20 and splits it into Oxygen and H+
    4. Electrons go Through the electron transport system
    Very close, but let me clarify something.

    The energy from the light displaces electrons that are in the reaction center.

    Think about it this way. You have a glass filled with water. That glass of water needs to remain full at all times. When you get thirsty, you drink it up. Since the glass needs to stay full, you immediately go fill it up again, until you get thirsty again and the cycle repeats.

    Think of the reaction center as that glass, the electrons as the water, and your thirst as the energy from light.

    The reaction center is sitting their with electrons filling it up. When light is absorbed, those electrons are removed. and the reaction center has to be filled up again. In order to fill it up, the Oxygen Evolving Complex (OEC) splits H2O and takes the electrons to fill in the holes.

    Now the electrons that were removed from the reaction center enter the electron transport system.

    5. Protons and electrons help form ATP from ADP and pi adding a phosphate to ADP Confused (not sure)
    6.electron has lost its energy from making ATP and is transported to PS1
    The electrons do not directly form ATP.

    What happens as the electrons move through the electron transport chain is that their movement causes protons to be transported from one side of the thylakoid

    Think of the electrons as water again and the electron transport chain as a water mill. As the water flows down hill, it turns the water mill. This provides energy to work.

    So the electrons are turning the water mill called the electron transport chain. Protons that are on the outside of the thylakoid are moved to the inside by this water mill.

    What this does is create a higher concentration of protons on the inside of the thylakoid then on the outside. This is important and I will use the water mill analogy again in a little bit.

    Think about the formation of the proton gradient as pumping water up a mountain. Water flows down hill, and the movement of that water can drive a water mill, but in order to do that it must first be uphill.

    At this point we have not formed any NADPH or ATP. All we have done is moved an electron out of the PSII reaction center and then used the downhill flow of the electron to pump protons uphill.

    6.electron has lost its energy from making ATP and is transported to PS1
    7.Light energy is transported to the reaction center where it re-energizes the electron.
    8. electron forms NADPH from NADP and H+
    Remember the analogy of the glass of water. Its the same deal. The PSI reaction center is a glass filled with water. The reaction center is the glass, the electrons are the water. Light removes the electron from the reaction center just like drinking the water removes the water from the glass.

    So now you have an empty glass that needs to be filled.

    The electrons that are coming out of the electron transport chain are like a faucet that fills the glass up again.

    The light removed the electron that originally sitting in the PSI reaction center, so that is replaced by electrons coming out of the electron transport chain.

    Now that original electron that removed from the PSI reaction center reduces a NADP+ to NADP. This allows NADP to bind to a H+ making NADPH.

    Now remember how we pumped those electrons from the outside of the thylakoid to the inside creating a gradient.

    Remember how I said this was analogous to pumping water up a hill?

    So now you have a pool of water on top of a hill.

    If you let it run down hill, it has energy that can turn a water mill.

    That water mill can be used to make energy to do work, like make electricity.

    So think about that proton gradient. As it moves from inside the thylakoid to outside the thylakoid (water flowing down a hill) it literally turns the enzyme ATP synthase (turning the water mill). This gives ATP synthase the energy to take ADP and phospate, pi, to make ATP.

    I hope that clarifies things.
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  7. #6  
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    look up diffusion and concentration gradients which help immensely with this topic. the protons move when the concentration gradient is more concentrated outside of the cell than inside. in order to restore balance the protons move inside and they produce ATP synthase, etc.
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  8. #7  
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    Quote Originally Posted by ronan
    5. Protons and electrons help form ATP from ADP and pi adding a phosphate to ADP :? (not sure)
    chadn737 has made a nice explanation about this point.
    Protons and electrons do not directly participate in the ATP synthesis.
    Transmembrane proton\electron transport generates potential on the membrane. This potential drives ATP synthesis.
    Another analogy would be electric power plant: electricity is generated at the plant (=PSI and PSII generate membrane potential), and the user-end like some home electrical devices is connected to the plant by wires (ATP synthase is coupled to the photosynthetic proteins via the membrane).
    If you look for a more detailed explanation, may be you would find http://www.atpsynthase.info helpful, especially the FAQ section.
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