BIO Electrophoresis. Electrophoresis is a process used by...

BIO Electrophoresis. Electrophoresis is a process used by biologists to separate different biological molecules (such as proteins) from each other according to their ratio of charge to size. The materials to be separated are in a viscous solution that produces a drag force $F_{\mathrm{D}}$ proportional to the size and speed of the molecule. We can express this relation- ship as $F_{\mathrm{D}}=K R v,$ where $R$ is the radius of the molecule (modeled as being spherical), $v$ is its its speed, and $K$ is a constant that depends on the viscosity of the solution. The solution is placed in an external electric field $E$ so that the electric force on a particle of charge $q$ is $F=q E$ . (a) Show that when the electric field is adjusted so that the two forces (electric and viscous drag) just balance, the ratio of $q$ to $R$ is $K v / E$ . (b) Show that if we leave the electric field on for a time $T,$ the distance $x$ that the molecule moves during that time is $x=(E T / k)(q / R)$ . (c) Suppose you have a sample containing three different biological molecules for which the molecular ratio $q / R$ for material 2 is twice that of material 1 and the ratio for material 3 is three times that of material 1. Show that the distances migrated by these molecules after the same amount of time are $x_{2}=2 x_{1}$ and $x_{3}=3 x_{1}$ . In other words, material 2 travels twice as far as material $1,$ and material 3 travels three times as far as material $1 .$ Therefore, we have separated these molecules according to their ratio of charge to size. In practice, this process can be carried out in a special gel or paper, along which the biological molecules migrate. (Fig. P21.94). The process can be rather slow, requiring several hours for separations of just a centimeter or so.

BIO Electrophoresis. Electrophoresis is a process used by biologists to separate different biological molecules (such as proteins) from each other according to their ratio of charge to size. The materials to be separated are in a viscous solution that produces a drag force $F_{\mathrm{D}}$ proportional to the size and speed of the molecule. We can express this relation- ship as $F_{\mathrm{D}}=K R v,$ where $R$ is the radius of the molecule (modeled as being spherical), $v$ is its its speed, and $K$ is a constant that depends on the viscosity of the solution. The solution is placed in an external electric field $E$ so that the electric force on a particle of charge $q$ is $F=q E$ . (a) Show that when the electric field is adjusted so that the two forces (electric and viscous drag) just balance, the ratio of $q$ to $R$ is $K v / E$ . (b) Show that if we leave the electric field on for a time $T,$ the distance
$x$ that the molecule moves during that time is $x=(E T / k)(q / R)$ . (c) Suppose you have a sample containing three different biological molecules for which the molecular ratio $q / R$ for material 2 is
twice that of material 1 and the ratio for material 3 is three times that of material 1. Show that the distances migrated by these molecules after the same amount of time are $x_{2}=2 x_{1}$ and $x_{3}=3 x_{1}$ . In other words, material 2 travels twice as far as material $1,$ and material 3 travels three times as far as material $1 .$ Therefore, we have separated these molecules according to their ratio of charge to size. In practice, this process can be carried out in a special gel or paper, along which the biological molecules migrate. (Fig. P21.94). The process can be rather slow, requiring several hours for separations of just a centimeter or so.

Thanks for your feedback!

Play audio

Feedback

Please give Ace some feedback