91.

Which one of the following inactives the serine/threonine protein kinase, mTOR, related to cell growth in mamalian system?

• Rifamycin 

• Rapamycin

• Erythromycin

• Chloramphenicol

Protein kinases are key regulators of cell's communication system, passing message along the signaling cascade . They are enzymes that attach phosphate groups of serine/threonine proteins or tryosine proteins in the cells, which then effectively passes the message like a bucket brigade.

The tryosine proteion kinases that do not have the ouside receptor portion or the transmembrane portion are called non-receptor tryosine kinases. They work to relay the message in the cytoplasm of cell to the nucleus (downstream signaling). There are 10 families, such as the jak, abl, and src. The other type of protein kinase is called the serine/threonine protein kinase. One example of a serine/threonine protein kinase is the mammalian target of rapamycin (mTOR), which plays a central role in cell proliferation (turning on the cell cycle) and cell metabolism and in regulating cell growth and angiogenesis. mTOR was named as such because Rapamycin, and immunosuppressant, was able to inhbit this kinase in organ transplant patients.