Recent content by twall11347243

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    Isothermal Settling (aka sedimentation equilibrium)

    Okay, so would you consider the cell to be 'isothermal'? I don't, but apparently it is according to this Paul Todd paper (See attached). Overall the cell may be 'isothermal' to maintain a constant 37 oC... but within the molecular environment there endothermic/exothermic reactions where heat is...
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    Diffusion = sedimentation at 1g?

    Right, we are not isothermal at the molecular scale hence endothermic and exothermic reactions, and there are other processes to prevent the equilibrium for ever happening but then why does the paper say it can affect cells? I don't understand why it's evening mentioning it- it makes me think...
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    Isothermal Settling (aka sedimentation equilibrium)

    Is anyone familiar with these terms or the experiments involved? I have a lot of questions regarding them. Thank you guys.
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    Diffusion = sedimentation at 1g?

    Plus the defintion is that once at equilibrium, there is no net mass transfer, no net transfer of chemical potential energy... we wouldn't be able to sustain life under these conditions. But, I'm confused because then why is the paper EVEN TALKING ABOUT THIS in the mammalian cell? The link...
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    Diffusion = sedimentation at 1g?

    I am confused on how this whole 'isothermal settling' process is even possible in the cell. I attached a screeshot, of a published work saying that isothermal settling is possible effect within the cell. It's condition is that the temperature T does not change over the height of a group of...
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    Diffusion = sedimentation at 1g?

    So the 1MDa will give a gradient eventually even at 1g? It's just so small we can't detect it? Or is it saying that because it under 1um it settles so slowly we can't detect the gradient because there is no gradient. The context of this excerpt is talking about 1g. It's not talking about in...
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    Diffusion = sedimentation at 1g?

    I appreciate your help. Thank you, Could you take a shot at interpreting this for me? See attached. I think it's saying that for a 1MDa protein who falls so slowly that you would never see the gradient in a realistic amount of time. But then that's why they started using shorter columns...
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    Diffusion = sedimentation at 1g?

    The peclet number is a ratio: gravitational potential energy/thermal energy Isothermal settling is done in situations where the peclet number is small (less than 0.1) (see attached) - which means that KT > mgh ... so how can you get isothermal settling (aka sedimentation equilibrium) if KT >...
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    Diffusion = sedimentation at 1g?

    I'm really not sure about TE = GPE... there's other factors like a 'Peclet number'... it's all really confusing. I am sure that diffusion = sedimentation at equilibrium, and that at equilibrium all the particles have the same kinetic energy and are in arrested state, not moving. But if...
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    Diffusion = sedimentation at 1g?

    See attached.
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    Diffusion = sedimentation at 1g?

    It should not. In your example, for the 10MDa it's thermal energy is significantly greater than its gravitational PE. Thus, rate of diffusion >>> rate of sedimentation. The definition of sedimentation equilibrium is that thermal energy = gravitational PE (and diffusion rate = sedimentation...
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    Diffusion = sedimentation at 1g?

    I attached a few pics. Can someone tell me, if this 'isothermal settling' happens even for very small molecules (say proteins inside the cell) at normal gravity? Something that small's thermal energy (KT) would be >>> much greater than it's gravitational potential energy (mgh) so it should...
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    Gravity's Effects on Cells: Isothermal Settling & Cellular Processes

    So what you're saying is that even if small particles do happen to form a stratification (where there's slightly more particles at the bottom compared to the top) it won't be much because of all the other cellular reactions mixing things up. Do you think this is all negligible for small...
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    Diffusion = sedimentation at 1g?

    But when Perrin did these calculations... he was dealing with colloids (grains) that are insoluble in water. But I'm talking about molecules that are dissolved in the cytosol forming a solution. This should create even more homogeneity (as far as density distribution at the top vs. bottom)...
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    Diffusion = sedimentation at 1g?

    Okay, I'm sorry. I just did a calculation now, (see my file #1) So according to the formula Lg is the length by which the density decreases by 37%. And let's use a massive particle (say 1,000 kDa). Lg = KbT/mg (1.38 x 10^-23) x (310 Kelvin for body temperature) / (1.66 x 10^-21) x (9.8)...
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