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The Structure and Funtion of the Cell Membrane

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The Structure and Funtion of the Cell Membrane The cell is recognized as the basic unit of all living things. There are two main types of cell in the living world and they are prokaryotic and eukaryotic. One thing which these cells have in common is the cell membrane. Cells probably would never have existed if it was not for the cenll membrane. The life of the cell depends on precise compartmentalization and organization of the proteins, nucleic acids, carbohydrates and small molecules. Membranes are found inside cells as well as around them defining the external boundary and they regulate the molecular traffic across that boundary, achieving compartmentalization. The membrane divides organelles such as the nucleus, endoplasmic reticulum, mitochondria and lysosomes into specialized compartments and thereby separate components and biochemical processes.(1) Membranes are central to cell-cell communication and cell movement and also organize complex reaction sequences such as the electron transport chain in mitochondria and photosystems in chloroplasts. ...read more.


There are not many strong chemical bonds holding membranes together. Instead membranes get their strength, great flexibility and mobility by a large number of weak interactions resulting from the properties of lipids. Permability studies showed that lipids could move easily between the interior of cells therefore it was decided that the cell membrane must contain lipids to allow fat soluble materials such as glucose, amino acids and ions to move across the membrane by being transported in it. In membranes the lipids are of a special kind called amphipathic lipids. The second type is the lipids bilayer or a `micelle' which is a single layer circle of phospholipids with the fatty acyl tails pointing inwards. The basic structural unit of virtually all biomembranes is the phospholipid bilayer. The bilayer is a sheet like structure composed of two layers of phospholipid molecules whose polar head groups face the surrounding water and whose fatty acyl chains form a continuous hydrophobic interior. ...read more.


The smaller molecules between the phospholipids is cholestrol. Cholesterol and its derivatives constitute another importat class of membrane lipids, the steroids. Cholesterol is the major constiuent of animal tissues. Although cholesterol is almost entirely hydrocarbon in composition it is amphipathic because it contains a hydroxyl group that interacts with water. Cholesterol in the membrane interacts with adjacent phospholipids making the membrane more rigid or stable. Another impritant but minor constituent of membranes is carbohydrate. When carbohydrate is attached to proteins it forms glycoprotein and when it is attached to lipids it forms glyclipid. In the plasma membrane, all the O- and N- lined oligosacharides in glycoproteins and all of the oligosacharides in glycolipids are on the exoplasmic surface. In the endoplasmic reticulum they are found on the interior membrane surface. Surface carbohydrates are known collectibely as glycocalyx and are usually oligosacharides which are positioned to aid in cell recognition functions. Glycocalyx act as antigens and are important in immune response. ...read more.

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