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Discuss the structure and functions of the cell membrane.

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Discuss the structure and functions of the cell membrane. The cell membrane surrounds all living cells. It controls how substances can move in and out of the cell and is responsible for many other properties of the cell as well. The membranes that surround the nucleus and other organelles are almost identical to the cell membrane. Membranes are composed of phospholipids, proteins cholesterol, glycoproteins and glycolipids arranged in a fluid mosaic structure. The phospholipids are arranged in a bilayer, with their polar, hydrophilic phosphate heads facing outwards, and their non-polar, hydrophobic fatty acid tails facing each other in the middle of the bilayer. This hydrophobic layer acts as a barrier to all but the smallest molecules, effectively isolating the two sides of the membrane. ...read more.


This enables cells to recognise other cells, and behave in an organised way, for example during development of tissues and organs in multicellular organisms. It also means that foreign antigens can be recognised and attacked by the immune system. Glycolipids also have branching carbohydrate side chains and are involved in cell-cell recognition. They may act as receptor sites for chemical signals. With glycoproteins they are also involved in sticking the correct cells together in tissues. The cell membrane also have several functions which include: osmosis, diffusion, active transport and exocytosis and endocytosis. Besides specialised cell membranes are the sites of important chemical reactions such as photosynthesis and respiration. ...read more.


The pump operates to maintain the concentrations of sodium and potassium in such a way that it replaces 2 potassium ions for every 3 sodium ions found in the cell. Secondary active transport does not use ATP directly but takes advantage of a previously existing concentration gradient but still can move materials against the concentration gradient. For example a glucose molecule bind with a sodium ion to cross the cell membrane. Endocytosis is the transport of materials into a cell. Materials are enclosed by a fold of the cell membrane, which then pinches shut to form a closed vesicle. Exocytosis is the transport of materials out of a cell. It is the exact reverse of endocytosis. Materials to be exported must first be enclosed in a membrane vesicle. ...read more.

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