Your lab is studying the effects of a potential new cancer drugs. Your task in t
ID: 205439 • Letter: Y
Question
Your lab is studying the effects of a potential new cancer drugs. Your task in the lab is to find out how these drugs works at the cellular level.
I. One drug was isolated from plants, and seems bind to a protein called CMB405. We don’t quite know what CMB405 is doing, or where it resides. You suspect that it may be a membrane associated protein, so you run a few tests on cells in culture to determine what it could be doing.
Test #1: You homogenize cells in buffer with very low salt concentration, and separate the plasma membrane (PM) fraction from the cytoplasm by differential centrifugation. The protein seems to segregate with the PM fraction.
Test #2: You homogenize cells in the same buffer but with very high salt concentration, and separate with differential centrifugation. Now the protein seems to be found in the cytoplasmic fraction (water soluble fraction).
A. What is the principle behind differential centrifugation that would allow us to separate the cytosol from the plasma membrane? (2 pt)
B. What type of protein (cytosolic, integral membrane, GPI-anchored or peripheral membrane) is CMB405? Explain your answer. (3 pts)
Explanation / Answer
A.
In differential centrifugation, separation of particles of a solution occur on the basis of mass of components of the solution and density .
Plasma membrane is heavier than the cytosol. So, when a centrifugal force is applied to the cell mixture, then the plasma membrane settles down as the pellet while the cytosol comes in the supernatant.
B.
The protein is peripheral. Peripheral membrane protein remains attached to plasma membrane under low salt concentration. If pH is increased or salt concentration is elevated, then, these proteins dissociate from the plasma membrane and move into the cytosol.
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