Occupy The Cell! 99% of the molecules in our cells are water, about 70% by weight .
“Water is life’s mater and matrix, mother and medium. There is no life without water”, so said Hungarian biochemist and Nobel laureate Albert Szent-Gyorgyi (1893-1986)
Water enters and exits the cell through water channels known as Aquaporins, embedded in the hydrophobic lipid membrane.
Aquaporins move water at the rate of 1/ns or 1 billion water molecules per second!
The animation shows water molecules squeezing through a narrow pore in a single file. One of them is labeled in yellow so you can watch its progress through the 10 ns simulation. Notice that the oxygen atoms (red) face the channel center, flipping in orientation in the middle of the pore. This is thought to break the chain of hydrogen bonds and prevent protons from tunneling through, which would destroy proton gradients and mess up cellular pH. (See Grotthuss mechanism: http://en.wikipedia.org/wiki/Grotthuss_mechanism)
Discovered by Hopkins scientist Peter Agre by accident (he was searching for the Rh antigen on blood cells); my colleague Bill Guggino tells the story of putting the unknown protein into frog eggs ( Xenopus oocytes, used because of their large size) to measure their function..but water rushing into the eggs made them explode, spattering yolk all over the microscope lens! Agre was awarded the Chemistry Nobel in 2003.
This molecular dynamics simulation is by Emad Tajkhorshid (http://csbmb.beckman.illinois.edu/) and is featured on the Nobel web site.