Smooth Endoplasmic Reticulum : Throughout the eukaryotic cell, especially those responsible for the production of hormones and other secretory products, is a vast network of membrane-bound vesicles and tubules called the endoplasmic reticulum, or ER for short. The ER is a continuation of the outer nuclear membrane and its varied functions suggest the complexity of the eukaryotic cell.
The smooth endoplasmic reticulum is so named because it appears smooth by electron microscopy. Smooth ER plays different functions depending on the specific cell type including lipid and steroid hormone synthesis, breakdown of lipid-soluble toxins in liver cells, and control of calcium release in muscle cell contraction.
Unlike eukaryotic cells, prokaryotic cells do not have a cell nucleus or any membrane-bound organelles such as mitochondria. Therefore neither the DNA of prokaryotic cells nor any of the sites of metabolic activity within a prokaryotic cell are enclosed by a separate membrane. Instead, everything is openly accessible within the cell . ribosomes are scattered throughout the cytoplasm (not attached to the surfaces of the endoplasmic reticulum as in animal cells). Examples of prokaryotic cells include the cells of many bacteria, . vibrio cholerae , the cholera bacterium.
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