Essay On How Are Proteins Transported Out Of The Nucleus

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How are proteins transported out of the nucleus?
The nucleolus in the nucleus acts as a site for the synthesis of ribosomes such as tRNA, mRNA, rRNA and ribosomal proteins. Therefore, these proteins need to be transported out of the nucleus to the cytosol to carry out their functions within the cytosol. So, how are proteins transported out of the nucleus? Generally, a sorting signal is incorporated into the protein to be transported. A sorting signal is a specific amino acid sequence designated for a specific location in the cell. It is recognized by a sorting receptor which is complementary to the signal sequence. This helps to direct the movement of proteins from its original location to the correct final destination. A typical sorting signal contains 15 to 60 amino acid residues and this sequence is found at the N-terminus of the polypeptide chain. Signal peptidases will cleave off the signal sequence from the protein once it reaches its destination. Occasionally, multiple amino acid sequences can arrange into a 3-dimensional structure, forming a signal patch on the protein. A nucleus is surrounded by nuclear envelope which is perforated by nuclear pore complexes (NPC). Proteins are exported from the nucleus to the cytosol by gated transport because
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The 8 identical nucleoporins are arranged in a circle. The nuclear fibrils extend into the nucleoplasm and cytosol. The function of the nuclear fibrils is to guide the proteins towards the pore of NPC. The end of fibrils are linked by a distal protein ring, forming a basket-like structure. Each NPC contains one or more aqueous passages. However, these proteins cannot pass through the NPC by passive transport. Due to their large sizes, these proteins are blocked by unstructured region of nucleoporins that form a tangled meshwork at the central pore of NPC. Thus, they need to be exported from the nucleus into the cytosol by active

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