a) The diffusion coefficient of a vesicle in a cell is on the order of 8 x 10^(-8) cm^2/s. A typical cell size is of order 100 microns across. How long would it take for a vesicle to diffuse across the cell (on average)?

b) Another way the body moves vesicles is to use use active transport along microtubules. Kinesin is a motor protein that plays a large number of roles in cellular motion and transport. Kinesin "walks" along microtubules using motor heads that bind to and release from the microtubule, propelling the kinesin and the cargo along and using up a molecule of ATP in step of the process. The overall velocity in vivo of the kinesin and its cargo is on the order of 1000 nm/second). How long would it take to move the vesicle across the same cell?

c) Diffusion is free - but active transport costs energy. Each kinesin step requires hydrolyzing one ATP, and moves the kinesin 8.5nm. Hydrolizing one mole of ATP releases 50kJ of energy. How much energy is required to use active transport to move a vesicle across the cell?