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The Role Of Biology And Macromolecules

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The presence of a nuclear envelope surrounding genetic code is the main defining feature that separates eukaryotes from prokaryotes. This compartmentalisation of the genome provides a novel way for a cell to control gene expression, as proteins and macromolecules that are synthesised in the cytoplasm and function in the nucleoplasm must be imported across the double nuclear membrane and vice versa.
~Nucleus is greek for kernel~
The nuclear envelope is made up of an inner and outer membrane, each with phospholipid bilayers which are connected at nuclear pores. Nuclear pores permeate the membrane and consist of 30 different nucleoporins. The outer membrane is continuous with the ER and is studded with ribosomes, and the inner membrane is
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Helps deform membrane to be highly curved. The inner tunnel of the pore contains FG-repeats, which are rich in the residues of basic amino acid phenylalanine and glycine repeats. FG associated with basket filaments at terminal ring. FG nups form a hydrophobic core, and occur in regions of extended hydrophillic polypeptide chains that fill the central transporter channel. Such nucleoporins which form a gel-like mesh line the channel, allowing diffusion of small non polar molecules of up to 40 kDa in size. All other proteins and macromolecules larger than 40kDa must be escorted through the pore by active and facilitated transport. Translocation into the nucleus differs to that of other organelles as they travel through a large expandable aqueous pore, allowing the passage of folded proteins as opposed to the extensive unfolding proteins must do in order to be cross other organelle membranes.
Nuclear localisation signals faciliatate transport
The best understood mechanism of transport across the nuclear membrane is driven by Ran. Ran is a monomeric G protein, it functions as a molecular switch that can exist in two conformations depending on whether it is bound to GTP or GDP.
Receptor mediated mechanisms transport molecules across efficiently, up to 1000 macromols per second or 60,000 imported molecules into the nucleus per minute (Lodish et
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