Ribosomes
Def: >>-Non-membranous rounded or oval bodies [12 X 25 nm] >>-Formed of strands of rRNA + associated proteins >>-Formed in the nucleolus, then pass to cytoplasm through nuclear pores -Found in large numbers in protein synthesizing cells
L.M: -Very minute structures (15-20 nm) -Difficult to be seen by
L.M. -Basophilic when stained by H+E [due to RNA content]
E.M: -Small electron-dense granules >>-Formed of 2 subunits (Large & Small) Forms: 1-Free: -Single or -In groups connected by mRNA strand → forming spiral chains (polysomes) >>2-Attached: To the outer surface of rER by the large subunit at receptors called [Ribophorins]
Function: Protein synthesis >>1-Free ribosomes: >>-Form proteins for local use in cytoplasm -Common in immature cells [Embryonic & Stem cells] >>2-Attached ribosomes: >>-Form proteins for export [secreted by the cells as enzymes & hormones]
Proteasomes
Def: >>-Very small non-membranous cylindrical protein complexes >>-Contain proteases Function: Degrade denatured or nonfunctional proteins
Considered as a quality control unit to ensure quality of exported proteins
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