Question

Please answer the following parts with good explanation. Thank you!

1A.)Explain how PIP2 is a membrane bound signaling molecule that can be modified by both GPCR and RTK pathways for different cell signaling pathways.

1B.) Why is it important that caspases are maintained in the cell as proenzymes prior to activation?

Answer 1

1.B. CASPASE is the acronym for “Cysteinyl aspartate specific protease”. They are proteases with cysteine in their active centre. Caspases 1 to 10 are identified; they are named in the order of their discovery. All these enzymes are secreted as inactive zymogen form; they are activated one by one. The caspase 8 is the first one activated , which is otherwise called the initiator. The final one is caspase 3, the executor of death, which is officially named as “Yama”, the Hindu God of Death. Caspase 3 will hydrolyze certain target proteins, like those maintaining cytoskeleton. Cytochrome c, when released from mitochondria into cytosol activates procaspase 9 to caspase 9. This causes activation of the whole pathway.

Thus, if caspases are not present in inactivated form, it can initiate a cell digestion or destruction process and the cell could die.

1.A. The major player in this type of signal transduction is phospholipase C that hydrolyses phosphatidyl inositol(PIP2) in membrane lipids to 1,4,5-Inositol triphosphate (IP3) and Diacyl Glycerol (DAG) that act as second messengers. PIP3 (Phosphatidyl Inositol 3,4,5- phosphate) is another second messenger produced by the action of a phosphoinositide kinase. The phospholipase C may be activated either by G-proteins or calcium ions.

when a signalling molecules bind with the receptor tyrosine kinase, the redemptive dimerises and auto phosphorylate each other. This cause activation of phospholiapse C, which then degrades PIP2 to IP3, and this IP3 gets phosphorylated by PIP3kinase to activate AKT protein, and thus propagate the signal.