Problem 17: Gel electrophoresis Gel electrophoresis. is a tremendously important
ID: 147781 • Letter: P
Question
Problem 17: Gel electrophoresis Gel electrophoresis. is a tremendously important analysis method, pervasive in biomedical research, that is used to separate different DNAs or proteins, one from another. Gel electrophoresis is one of the key techniques involved in DNA fingerprinting which enables detailed genetic comparisons between and within species, and has therefore revolutionized our understanding of evolutionary relationships among and within species. DNA fingerprinting also has societal impact because it which permits forensic scientists to implicate or exonerate suspects in criminal investigations, and has revolutionized justice systems around the world in the last 20 years, including the US justice system. This problem illustrates the role of Newton's second law and terminal velocity in gel electrophoresis. It also illustrates the role that an understanding of terminal velocity can play in providing a conceptual framework within which to learn something new and interesting about the transport properties of (unfolded) proteins through a gel network. Finally, it will permit you to gain experience in examining, analyzing, and explaining experimental measurements, and in developing hypotheses based on those measurements 9 Material delrin steel air bubble canola oil water octane Karo syrup human blood true blood Density (g cm-3) Viscosity at 23°C (centipoise) 1.415 7.85 0.001 0.915 1.000 0.703 1.33 1.06 1.06 0.01 40-60 0.5 3000 3.5 (7 C) 3.5 (7 C) 3 Table 2.1: Properties of several relevant materials and fluids. Note that centipoise is the cgs unit of viscosity. 4Explanation / Answer
a)
In gel electrophoresis, DNA/ protein molecules reaches terminal velocity very soon. As when the the electric field is applied, the frictional drag force because of the immersion of the molecule in fluid exactly cancels the electric force and the acceleration a becomes zero. Thus, the molecule attains terminal (steady-state) velocity , and possess only terminal speed where the distance travelled can be compared with its molecular weight under a given period of time.
b)
Terminal velocity is also dependent upon the electrophoretic mobility () of the molecule i.e., v=E, which depends on the molecular size and confirmation of the molecules. Thus, the molecules with different sizes will have different terminal velocity.
c)
Larger the size of the molecule, higher will be the resistance and lower will be the mobility of the molecule. Thus, a molecule with larger size will move shorter distance in comparison to a small sized molecular under a given period of time.
d) SDS or Sodium dodecyl sulfate is an anionic (negatively charged) detergent. On an average, one SDS molecule binds to two amino acids and confers negative charge.
Thus, converting the the protein sample unanimously into negatively charged entity.
Hence, the rodlike SDS-protein complex is separated based on its terminal velocity ;dependent on the electrophoretic mobility and now we know that this electrophoretic mobility depends on coofirmation and size of the protein molecules subjected to gel electrophoresis.