plasma or cell membrane is a laminate structure which comprises the cell, defines its boundaries and helps maintain the balance between the inside (intracellular medium) and outside (extracellular) of them. In addition, similar to the membranes that delimit the organelles of eukaryotic cells.
is composed of a sheet that serves as a "container" for the cytosol and internal compartments of the cell, and also provides mechanical protection. It consists mainly of phospholipids (phosphatidylethanolamine and phosphatidylcholine), cholesterol, carbohydrates and proteins (integral and peripheral).
The main feature of this barrier is its selective permeability, allowing you to select the molecules that must enter and exit the cell. In this way remains stable intracellular environment, regulating the flow of water, ions and metabolites, while maintaining the electrochemical potential (making the internal environment is negatively charged).
When a large molecule passes through or is expelled from the cell and invagination of the plasma membrane to coat when inside respectively occur endocytosis and exocytosis processes.
has an approximate thickness of 7.5 nm and is not visible by light microscopy but electron microscopy, where you can see two layers and a central dark side more clearly. In prokaryotes and eukaryotes such as plants and fungi osmótrofas, is placed under another layer, called the cell wall.
is composed of a sheet that serves as a "container" for the cytosol and internal compartments of the cell, and also provides mechanical protection. It consists mainly of phospholipids (phosphatidylethanolamine and phosphatidylcholine), cholesterol, carbohydrates and proteins (integral and peripheral).
The main feature of this barrier is its selective permeability, allowing you to select the molecules that must enter and exit the cell. In this way remains stable intracellular environment, regulating the flow of water, ions and metabolites, while maintaining the electrochemical potential (making the internal environment is negatively charged).
When a large molecule passes through or is expelled from the cell and invagination of the plasma membrane to coat when inside respectively occur endocytosis and exocytosis processes.
has an approximate thickness of 7.5 nm and is not visible by light microscopy but electron microscopy, where you can see two layers and a central dark side more clearly. In prokaryotes and eukaryotes such as plants and fungi osmótrofas, is placed under another layer, called the cell wall.
Chemical composition:
The chemical composition of the plasma membrane varies between cells depending on the function or tissue in which they are, but you can study general. The plasma membrane consists of a double layer of phospholipids by proteins linked covalently not to that bilayer and carbohydrates covalently linked to lipids or proteins. The largest molecules are the lipids , since it is estimated that for every 50 lipids is a protein. However, the proteins due to their larger size, represent approximately 50% of the mass of the membrane.
Lipids: 98% of lipids in cell membranes are amphipathic , ie which have a hydrophilic end (which has an affinity and interacts with water) and a hydrophobic end (water repellent). The most abundant are phosphoglycerides (phospholipids ) and sphingolipids, which are found in all cells, followed by the glycolipids and steroids (especially cholesterol ). The latter are absent or scarce in the plasma membranes of prokaryotic cells . There are also neutral fats , which are amphipathic lipids, but only represent 2% of total membrane lipids.
phosphoglycerides. They have a glycerol molecule with which a esterified phosphoric acid and two fatty acids long chain, the major membrane phosphoglycerides are phosphatidyl or cephalin and phosphatidylcholine or lecithin . Sphingolipids
. Membrane lipids are composed of ceramide (sphingosine + fatty acid), only the family of sphingomyelin has phosphorus the rest have carbohydrates and thus are called glycosphingolipids or simply glycolipids. The have mainly cerebrosides glucose, galactose and its derivatives (such as N-acetylglucosamine and N-acetylgalactosamine ). The gangliosides contain one or more units of N-acetylneuraminic acid ( sialic acid).
phosphoglycerides. They have a glycerol molecule with which a esterified phosphoric acid and two fatty acids long chain, the major membrane phosphoglycerides are phosphatidyl or cephalin and phosphatidylcholine or lecithin . Sphingolipids
. Membrane lipids are composed of ceramide (sphingosine + fatty acid), only the family of sphingomyelin has phosphorus the rest have carbohydrates and thus are called glycosphingolipids or simply glycolipids. The have mainly cerebrosides glucose, galactose and its derivatives (such as N-acetylglucosamine and N-acetylgalactosamine ). The gangliosides contain one or more units of N-acetylneuraminic acid ( sialic acid).
Proteins:
The protein content ranges from 20% in the myelin sheath of neurons and 70% in the membrane 80% mitochondrial inner are intrinsic, while the remaining 20% \u200b\u200bare extrinsic. Proteins are responsible for the dynamic features of the membrane, so that each membrane has a very specific provision of protein intracellular membranes with a high proportion of proteins due to the high number of enzymatic activities that they host. In membrane protein plays several roles: conveyor, connecting (linking the membrane with the extracellular matrix or on the inside), receptors (responsible for cell recognition and adhesion) and enzymes. According to their degree of association to the membrane are classified as:
-> Integral or intrinsic : They have hydrophobic regions, for which you can associate within the membrane and hydrophilic regions that located outward, therefore, are amphipathic. Only be separated from the bilayer if it is destroyed (eg with a neutral detergent). Some of these, presents carbohydrate covalently attached to them (glycoproteins).
-> Peripheral or extrinsic : Neither hydrophobic regions and therefore can not enter into the membrane. They are on the inside of this (inside cell). Separate and join this with ease by ionic-type bonds.
-> Integral or intrinsic : They have hydrophobic regions, for which you can associate within the membrane and hydrophilic regions that located outward, therefore, are amphipathic. Only be separated from the bilayer if it is destroyed (eg with a neutral detergent). Some of these, presents carbohydrate covalently attached to them (glycoproteins).
-> Peripheral or extrinsic : Neither hydrophobic regions and therefore can not enter into the membrane. They are on the inside of this (inside cell). Separate and join this with ease by ionic-type bonds.
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