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TOPIC 17 - TOPIC 17 The Endomembrane System and the...

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TOPIC 17: The Endomembrane System and the Endoplasmic Reticulum The eukaryotic cell is packed with membranes and these do more than compartmentalize! Proteins which 'do their thing' in the cytosol are usually just dumped there following translation on 'free' ribosomes Proteins destined for secretion from the cell or incorporation into the ER membranes or the membranes of other organelles are usually synthesized on the rER The endoplasmic reticulum (ER) is a continuous system of flattened sacks and tubules specialized for protein modification and lipid biosynthesis and it has a surface that is thirty times that of the plasma membrane. The ER also forms the outer nuclear envelope, and ER pumps and channels, controls cytoplasmic [Ca 2+ ] whilst ER enzymes metabolize drugs. Additionally, the rough ER (rER) has numerous associated ribosomes that work with the ER to work together to insert proteins into the ER membrane or cisternae (space inside the ER) of the ER. Some of these proteins are retained here but most are moved out to other parts of the cell or are secreted from the cell. Indeed,
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