What are the major differences between phagocytosis and pinocytosis? endosome an

Question

What are the major differences between phagocytosis and pinocytosis? endosome and phagosome What are the different features of a receptor mediated-pinocytosis? What are the different fates of receptor proteins involved in endocytosis? What is the function of the Ran protein in nuclear soluble protein transport? What is the source of energy that drives the transport of the nuclear transport receptor back into the cytoplasm? What is the function of the SRP in protein transport across/in membranes of organelle? What is/are the functions of chaperones in protein transport? Are proteins transported through membrane pores, folded? Are proteins transported across membrane folded? Are signal sequences present always at the N-terminal end? Are signal sequences always degraded after the protein reaches its destination? Do all proteins have a transit peptide sequence? How many stop and start transfer sequences will an ER protein having 10trans- membrane segments have? Name the signal sequence present in ER luminal proteins. Where do Clathrin and COP coated vesicles originate and where is their final destination? Which proteins play a role mainly in the docking and fusion of transport vesicles, respectively? What is the function of NSF? What is the full name of SNARES? Which type of vesicles, are used by B lymphocytes, to secrete antibodies? How is cystic fibrosis and type 2 diabetes caused? How does Mycobacterium evade our immune system? What is UPR? What are the different outcomes of UPR? Which chemicals are taken up by our body using the receptor mediated-pinocytosis?

Explanation / Answer

1.Phagocytosis happens when a cell engulfs a solid particle.They can be large particles. Pinocytosis happens when a cell ingests the extracellular fluid. here smaller vesicles are formed, compared to phagocytosis. In phagocytosis, the solid particle is broken down for cellular absorption to take place.But in pinocytosis there is no need for this ,as it is an ingestion of already dissolved substances. There is the formation of pseudopodia in phagocytosis and there is no such formation in pinocytosis. Only invagination takes place in pinocytosis.

Phagosome is formed when a cell ingests a solid particle,present outside the cell.that is after phagocytosis.This may later fuse with an endosome. Endosome is already present in the cell as a membrane bound compartment,which originates from golgi apparatus.

2.Ran aid in the transport of proteins .,t RNA and ribosomal subunits from cytoplasm to the nucleus(exportins) and also from nucleus back to the cytoplasm(importins). Ran binds to these importins and exportins and regulate their cargo shuffling.Ran is associated with GTPases. The source of energy that transports nuclear receptors into cytoplasm is GTP, arising from Ran- GTP complex.

3.Signal Receptor Particle is a dimer, located on the rough Endoplasmic Reticulum in the cells. SRPs bind to the nascent polypeptide chain that has come from the ribosome.SRP has an affinity to the ribosome also. So it binds to the ribosome and then this complex binds to ER membrane, due to interaction of SRP with the receptor protein.However SRP is not involved in the protein translocation across the membrane.But the interaction of SRP, with the ribosome with signal sequence aids in translocation.

Chaperones or Heat shock proteins are help in the folding or unfolding of newly synthesized polypeptides.They bind to the nascent polypeptide on the ribosomes and prevent premature folding also.

4.The newly synthesized polypeptide is folded in the lumen of ER after its translocation into endoplasmic reticulum., with the help of chaperones. It then goes to the golgi complex

5.There is a short sequence of aminoacids at the amino terminus (N- terminus )of a newly synthesized polypeptide. No, in some secretoty proteins, the signal sequence is not located in amino terminus.

This sequence directs the polypeptide to its location in the cell.This signal sequence is cut off in the lumen of ER, by an enzyme signal peptidase.They are cleaved before the protein gets released ,in those that have to be a part of the membrane.So they are removed before the protein is released out of the ER.

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