Monday, September 6, 2010
After looking at Figure 7.2 I wondered how on earth could anything move within a cell that crowded. Even with ATP powering the movements of vesicles and the like, with something so densely packed surely no movement was possible. Furthermore specific reactants would never be able to find each other. It would be like trying to push to the front of a mosh pit at an epic concert.
However, a great explanation followed this picture. Nelson was able to explain that movement of larger molecules was possible due to the entropic forces of smaller molecules. By removing the depletion layer surrounding large molecules the entropy of the smaller ones could increase. This was achieved by sheparding the larger molecules together.
The depletion layer is a result of the smaller particles not being able to occupy (or concentrate in) the space directly surrounding the larger particles i.e they cannot occupy the maximum number of states, they're not at the maximum entropy. The entropy is maximised by decreasing the size of the depletion layer. Where the biggest decrease is seen when the large molecules are 'matching'. That is the larger molecule reactants are pushed toward the recognition sites of their specific enzymes speeding up the reaction. It's more like crowd surfing in a mosh pit, with everyones hands (the smaller molecules) propelling your body (the larger molecule).
It is amazing how so many processes, that at first seems backward, happen because of entropy.
It also made me wonder. Is this how bacteria are able to feed in laminar fluid? Do these 'sheepdogs' herd the food particles for the bacteria to eat?
Posted by Heather at 9:14 PM