Cyclization between Ser and Gly is probably rapid, and the oxidation of the Tyr side chain (by O2) is probably the rate-limiting step of fluorophore generation.

TLS Online TPP Program

#Id: 7772

#Unit 2. Cellular Organization

The inner membrane is surrounded by the outer nuclear membrane, which is continuous with the membrane of the ER. The outer nuclear membrane is studded with ribosomes engaged in protein synthesis.

TLS Online TPP Program

#Id: 7773

#Unit 2. Cellular Organization

Transport of proteins from the cytoplasm into the nucleus and movement of macromolecules, including mRNAs, tRNAs, and ribosomal subunits, out of the nucleus occurs through nuclear pores, which span both membranes of the nuclear envelope.

TLS Online TPP Program

#Id: 7774

#Unit 2. Cellular Organization

Each nuclear pore is formed from an elaborate structure termed the nuclear pore complex (NPC), which is one of the largest discrete protein assemblages in the cell.

TLS Online TPP Program

#Id: 7775

#Unit 2. Cellular Organization

The total mass of the pore structure is 60,000– 80,000 kDa in vertebrates, which is about 16 times larger than a ribosome.

TLS Online TPP Program

#Id: 7776

#Unit 2. Cellular Organization

In one minute, each NPC is estimated to import 60,000 protein molecules into the nucleus, while exporting 50–250 mRNA molecules, 10–20 ribosomal subunits, & 1000 tRNAs out of the nucleus.

TLS Online TPP Program

#Id: 7777

#Unit 2. Cellular Organization

An NPC is made up of many copies of some 30 different proteins called nucleoporins.