Cell Structure for Physiology of Fluid Balance P1

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Cell Membrane The cell membrane is a thin semi-permeable membrane that surrounds the cytoplasm of a cell. The membranes function is to protect the integrity of the interior of the cell by allowing certain substances into the cell, while keeping other substances out. It is a fluid phospholipid bilayer embedded with proteins and glycoproteins. The phospholipid bilayer is arranged so that the polar ends of the molecules (the portion of the phospholipid that is soluble in water) form the outermost and innermost surface of the membrane while the non-polar ends (the fatty acid portions of the phospholipids that are insoluble in water) form the centre of the membrane Nuclear Membrane It is a double-layered membrane enclosing the nucleus of a cell that controls what enters and leaves the nucleus. It can also be called nuclear envelope. The nuclear envelope has two membranes, each with the typical unit membrane structure. They enclose a flattened sac and are connected at the nuclear pore sites. The outermost membrane is continuous with the RER and has ribosomes attached. The space between the outer and inner membranes can fill with newly synthesized proteins just as the rough endoplasmic reticulum does. The nuclear envelope is enmeshed in a network of filaments for stability. Phospholipid Bilayer Both the cell surface membrane and the membranes surrounding certain organelles have the same basic structure. Much of the membrane is made up of what is known as a Phospholipid bilayer. The phospholipids are arranged in two layers (a bilayer). The phosphate heads are polar molecules and so are water-soluble. The lipid tails are non-polar and therefore are not water-soluble. This means that the phospholipids are arranged with the heads in contact with the cytoplasm which is a watery environment. The tails are protected from this, by being as far from the cytoplasm as

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