Attachment organelle

Microtubule-associated proteins bind to microtubules in vivo and subserve a number of functions including the promotion of microtubule assembly and bundling, chemomechanical force generation, and the attachment of microtubules to transport vesicles and organelles (Olmsted, 1986). Tubulin purified from brain tissue by repeated polymerization-depolymerization contains up to 20% MAPs. The latter can be dissociated from tubulin by ion-exchange chromatography. The MAPs from brain can be resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). 

Other proteins within the organelle catalyze folding of the protein, often attaching cofactors or oligosaccharides and assembling them into active monomers or oligomers. 

Ribosomes (79-87) are small organelles 17-23 nm in diameter. They can exist in clusters known as polysomes or be attached to the er where they bind to pores in the er membrane. A major constituent of the er pore is translocon, the heterotrimetric Sec 61 protein complex. Sec 61 binds to the 80s ribosomes (86). Ribosomes consist of subunits, a 30s subunit (16srRNA and 21 proteins), and a 50s subunit (23s and 5s RNAs, > proteins and the catalytic site of peptidyl transferase). Ribosomes are the sites of protein synthesis. 

Polysomes are organelles consisting of ribosomes and mRNA created when several ribosomes are attached, at about 100 nucleotide... 

The plasma membrane forms a boundary between the extra- and intracellular environments whereas membranes within a cell form boundaries between the organelles and the cytosol. These are discussed in other chapters, whereas the material in this chapter focuses on the plasma membrane. A primary function of this membrane is to serve as a barrier to prevent the entry of some molecules and ions into the cell and to retain others within the cell (Table 5.1). The plasma membrane has other roles, which are related to the presence of proteins within or attached to the membrane. These are ... 

Certain proteins destined for the plasma membrane or odier organelles are modified by the covalent attachment of sugar residues within the ER. This glycosylation represents a dynamic structure, which is repeatedly trimmed and re-synthesized by a multitude of enzymes. Surprisingly, the inhibition of... 

PS is inside the cell, it could attach to certain molecules /organelles and, after absorption of lighf, could cause fheir damage. This results in the disruption of essential mefabolic pafhways and subsequently causes the death of fhe cell. Bofh processes can proceed simulfaneously. The input of each process info fhe phofokilling mosf probably depends on the t)tpe of cell and PS, as well as on fhe environmenf. 

Within the living cell the great majority of the enzymes are attached to membrane structures or contained in cell organelles. When enzymes are isolated, they are removed from their natural state and quite often are highly unstable. The artificial binding of enzymes into membranes makes possible study of the interaction between diffusion and enzyme reaction within a well-defined context.1... 

The Hook family of proteins resembles CLIPs in that they consist predominantly of coiled-coil. However, the N-terminal domains, which attach to microtubules, differ in sequence from other known microtubulebinding domains. The C-terminal domains are adapted to bind specifically to particular organelles. Hook3, for example, appears to play a role in defining the architecture and localization of the mammalian Golgi complex (Walenta et al., 2001). This helps to explain why the integrity of the Golgi complex is completely dependent on the presence of the microtubule network. 

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