Question

In a subcellular localization technique, it is found that 50% of the protein is present at the plasma membrane and 50% is in the nucleus after PAGE analysis. Propose a biological explanation for these findings.

Answer 1

After synthesizing proteins in the cytoplasm they are targetted to the plasma membrane for secreting outside the cell (extracellular) and other membrane bound oranelles inside the cell (intracellular) according to the requirements of functions. This process of protein targetting to the plasma membrane is known as co-translational protein targetting and the process of proteins tragetting to the organelles (nucleus, mitochondria, peroxisome, etc.) is known as post-translational protein targetting. So, basically in the co-translational protein targetting, the proteins are following the pathway which is initially getting into the lumen of endoplasmic reticulam (ER), then transferred to the trans-golgi via COP-I protein, then finally to the plasma membrane via AP-II and clathrin mediated pathway. In the other process, the proteins after synthesizing in the rough ER they are transported to the nucleus or other membrane bound organelles according to the signals.

So, there are possibilitis of getting proteins in the plasma membrane (extracellular) and nucleous or other organelles (intracellular). This above PAGE results of getting 50% of protein in the nucleus and 50% of proteins in the plasma membrane is possible.