It has already been noted that carbohydrate is present in the plasma membrane as short, sometimes branched chains of sugars attached either to exterior peripheral proteins (forming glycoproteins) or to the polar ends of phospholipid molecules in the outer lipid layer (forming glycolipids). No membrane carbohydrate is located at the interior surface. The oligosaccharide chains of membrane glycoproteins and glycolipids [...]
Among all animal and plant cells, none has been more extensively studied than the mammalian erythrocyte or red blood cell. The erythrocyte has long been the favorite of investigators studying the plasma membrane because relatively pure membrane preparations are easily obtained. The mature erythrocyte contains no nucleus, mitochondria, ribosomes, endoplasmic reticulum, or other organelles; instead, this highly specialized cell consists [...]
All of a cell's proteins are synthesized by ribosomes, including, of course, those proteins that are destined for inclusion in the plasma membrane. Cytoplasmic ribosomes in eukaryotic cells occur in two states: (1) "attached" (ribosomes associated with the membranes of the endoplasmic reticulum) and (2) "free" (ribosomes freely dispersed in the cytosol). Both attached and free ribosomes are believed to [...]