LIFE 210 Lecture Notes - Active Transport, Membrane Potential, Peptide
Document Summary
125 million daltons, composed of 30 different proteins which are present in multiple copies and arranged in octagonal symmetry. The size cut-off to free diffusion through the npc is 60,000 daltons. Proteins such as dna polymerases cannot diffuse passively through the npc. Signal can be located almost anywhere in the protein. Because nuclear localization signals are not cleaved off, nuclear proteins can be imported repeatedly, for example after mitosis when nucleus reassembles. There are several receptors that bind specific nuclear localization signals. They bind both to the cargo protein and to npc proteins (fg repeats) The ran gtpase imposes directionality on transport through npcs. Nuclear import requires energy: hydrolysis of gtp by the gtpase ran. There is a gradient of two conformational forms of ran (gdp or gtp bound) Nuclear import receptor moves through nuclear pores bound to ran. Mitochondria are produced by growth and fission of preexisting organelles. Most proteins reach the mitochondria by post-translational transport from the cytosol.
