1. In the cell, forces are picoNewtons (pN) and the length scales are nanometers
ID: 1276631 • Letter: 1
Question
1. In the cell, forces are picoNewtons (pN) and the length scales are nanometers (nm). A molecular motor name Kinesin has a mass of about 100000 Da (dalton). One Da = 1.66 x 10^-27 kg. (a) Calculate the force of gravity on kinesin and express it in pN. (b) Kinesin walks along microtubules and transports vesicles around the cell. The biggest force acting against it is viscous drag. kinesin can generate a maximum force of about 20 pN to overcome the drag forces that act against it. How many times its weight is this force? Think about this in comparison to how much the strongest humans can lift. 2. The most important energy scale inside a cell is kb T, where k b is Boltzman's constant (kb = 1.38 x 10^-23 J/K) and T is room temperature, 295 K. Any energetic process that has an energy on the scale of k b T can be thermally activated. Many important biological bonds are only a couple k b T of energy. (a) Calculate kb T in terms of the familiar energy unit of Joules = lkg.m. (b) Convert your result in (i) to the unit of work/energy most useful for cell biology, pN.nm.Explanation / Answer
1)a)F=mg=10^5*1.66*10^-27*9.81N=1.63*10^-21N=1.63*10^-9pN
b)Ratio with weight=20pN/1.63*10^-9pN=1.23*10^10 times
A human can approximately left as much as he weighs.
2)a)kbT=1.38*10^-23*295=4.07*10^-21J
b)1pN.Nm=10^-12N*10^-9m=10^-21J
kbT=4.07pN.Nm
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