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Basic Question

  1. Sep 23, 2005 #1
    When a cell replicates itself, where does it get the matter to do so? I mean, cells can't just makes copies out of nothing, right?
     
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  3. Sep 23, 2005 #2

    Monique

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    Cells get their nutrients from their environment. Ultimately the energy comes from the sun, which plants use for photosynthesis, the top of the food chain (there are some organisms that use other forms of energy to start the food chain).
     
  4. Sep 23, 2005 #3
    To: lifeisareaction

    The "matter" for cell replication comes from the "energy" in the bonds of the resting ATP molecule. When the cell needs energy to replicate, one P goes into solution and is lost from ATP and in the process ADP is formed + "energy". Now, from E = Mc^2 we know that there is an equivalence of mass and energy. Thus, this bond energy that is released has all of properties of mass.

    So, to answer your question, you are correct that the cell does not start the process of making copies of itself "out of nothing". It starts the process by using energy that was already present in the resting ATP molecule. Thus, when the replication process is completed, there is no gain or loss of either energy or mass, they have just changed form. Recall from physics, energy (nor mass) can neither be created nor destroyed--only change forms.
     
  5. Sep 24, 2005 #4
    Cell replication just means that the cell divides in two cells, so the new cells are both half the size of the original cell. After the division the new cells may grow using matter in their surroundings. When grown enough they themselves may divide.
     
  6. Sep 24, 2005 #5

    Monique

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    This is absolutely not true. The energy from the ATP bond is not converted into any mass, it is used to power other reactions.
     
  7. Sep 24, 2005 #6
    I did not say the "energy of the bond is converted into mass", I said that the energy of the bond "has all the properties of mass". The bond energy of resting ATP begins as energy, and when ADP + P are formed, it ends as energy. However, because E = Mc^2, the bond energy also begins as mass and ends as mass as well. Energy and mass are equivalent, and in an ultimate sense they are identicle and are co-present always, two aspects of the same thing.

    The initial question was;

    When a cell replicates itself, where does it get the matter to do so?

    The "matter" (thus "energy") is in the resting ATP molecule. Another form of the question could have been: ...where does it get the energy to do so....
    Ultimately they are the SAME QUESTION, and the SAME ANSWER--from ATP.
     
  8. Sep 24, 2005 #7

    selfAdjoint

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    This is just bunk. The factor c-squared in the Einstein formula means it takes astronomical amounts of energy to equate to a typical cell mass. The mass equivalent of the ATP energy would be way way after the decimal point in proportion to the cell mass. When a cell divides the daughter cells are smaller. To a very high approximation mass is conserved apart from energy.
     
  9. Sep 24, 2005 #8

    Moonbear

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    The question was not where does the "energy" come from, it was where does the "matter" come from. Gerben has appropriately answered the question by recognizing that this word choice indicates the OP was confusing cell division with cell growth.

    While the energy for cell division does come from breaking of bonds (not only from ATP), it would be misleading to say it's the same as matter because energy can form matter. Afterall, the energy from those phosphate bonds is not being used to directly form the carbon or oxygen or nitrogen or even the phosphate atoms being used to form biological molecules, it is only being used to provide the energy to form the bonds between atoms to form molecules. There is no conversion of energy to matter there; the energy from a broken bond is transfered to new bond energy...energy to energy (and Monique is also correct that the initial source of energy is provided as solar energy in photosynthetic organisms, which are then consumed by other organisms that need to utilize that energy). The matter is coming from sources external to the cell (you can't grow cells without providing organic molecules as nutrients).
     
  10. Sep 24, 2005 #9
    I do not see that the OP confused cell replication with cell growth--they knew exactly the difference by use of the words "make copies out of nothing". Originally Posted by lifeisareaction When a cell replicates itself, where does it get the matter to do so? I mean, cells can't just makes copies out of nothing, right? Where OP is confused, is that they should have used the word "energy" not "matter". Of course the cell gets its matter ultimately from external sources, but OP is not confused on that point either. It was my read that they thought that matter just appeared out of nothing and was used for the replication process. Given the massive confusion (I see now caused by me over thinking the post more than OP), let me re-state my answer: ...You are right lifeisareaction, cells do not make copies out of nothing, they make copies out of the energy found in the ATP molecule. I will be more careful in my wording in the future.
     
  11. Sep 24, 2005 #10

    Moonbear

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    No, that's still not correct. The replication that goes on before cell division, such as duplication of chromosomes and organelles, requires more than just ATP. The bond energy released when ATP is converted to ADP is not enough to create new matter! The matter already exists in the form of nutrients absorbed by the cell from the environment. Even photosynthetic organisms need to extract nutrients and water from soil.

    Cell division itself (the formation of two cells from one) is a pinching off of the cell and does not require making copies of anything.

    Then, the later growth of the two smaller daughter cells is not part of cell division/replication.
     
  12. Sep 25, 2005 #11
    I owe this thread an apology, because it is important for young people to understand that when mistakes are made, mistakes should be acknowledged. I most apologize to poor "Lifeisareaction", hopefully not already driven away from science to business major for lack of clear response to what they titled "Basic Question".

    Sometimes what seems like a simple question can be open to different interpretation. My interpretation about what was asked about "making copies out of nothing" during replication of chromosomes was clearly incorrect, as discussed above by Moonbear, selfAdjoint, Monique. :redface:
     
  13. Sep 25, 2005 #12

    Moonbear

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    No need for apologies (acknowledging a mistake doesn't mean anyone needs to apologize for it; honest misunderstandings happen, and it doesn't mean you did anything wrong that requires an apology). People with different backgrounds will latch onto different parts of a question, and it is through the discussion that the question becomes clarified.

    There are two things worth pointing out for everyone's benefit that came out of this:
    1) In biology (and all sciences really), precise wording is very important. Every student needs to be aware of this, particularly when learning terminology. Changing a single word can change the entire meaning of a definition or the interpretation of a question.
    2) There is a challenge in teaching that requires reading or hearing a student's question and recognizing in that question if there is a misunderstanding of another concept aside from the one being directly asked, or what the actual question being asked is. Students, please be patient with your teachers/professors if they don't answer your question directly or misunderstand your question, and don't be embarrassed if we can't understand your question...it's all part of the learning process not only to learn how to answer questions, but to learn how to ask them. It's tough to ask a question if you don't understand something well enough to form the right question, and we know this and can empathise.
     
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