Membranes160 - Membrane Structure and Function - 1 The Cell...

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Membrane Structure and Function - 1 The Cell Membrane and Interactions with the Environment Cells interact with their environment in a number of ways. Each cell needs to obtain oxygen and other nutrients (carbohydrates, amino acids, lipid molecules, minerals, etc.) from the environment, maintain water balance with its surroundings, and remove waste materials from the cell. The boundary between any cell and its environment (through which substances must pass) is the plasma membrane, composed of phospholipid and protein molecules. Plasma Membrane The plasma membrane has a number of functions for a cell. Serves as the boundary between the cytoplasm of the cell and the external environment, and selectively isolates the cell from the external environment. Maintains the cell's environment by regulating materials that enter or leave the cell. (Anything that enters or leaves the cell must pass through the membrane). We often say that a membrane is selectively or differentially permeable for this reason. Provides mechanisms for cell-to-cell communication. Provide mechanisms for cell-to-cell and within the cell attachments. Genetically unique cell recognition markers embedded in the plasma membrane provide mechanisms for a cell to recognize itself and other cells of its particular individual organism versus non-self (foreign materials). This is important to the immune system and defense of the organism. Although the plasma membrane forms the boundary of the cell, and surrounds the cell, many internal structures of most cells also have their own membrane boundaries. Much of what we say about membrane structure and function at this time applies to all membranes. The Fluid Mosaic Membrane Structure The typical membrane structure consists of a phospholipid bilayer with a number of proteins scattered throughout, along with some carbohydrates (glycoproteins), glycolipids and sterols, similar to the way in which one does a mosaic tile, hence the name.
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Membrane Structure and Function - 2 Phospholipid Bilayer A phospholipid has both polar and non-polar regions. The fatty acid "tails" of the two phospholipid layers are oriented towards each other so that the hydrophilic "heads", which contain the phosphate portion, face out to the environment as well as into the cytoplasm of the cell's interior, where they form hydrogen bonds with surrounding water molecules. Because the individual phospholipid molecules are not bonded to each other, a membrane is flexible (or “fluid”), something which is pretty important to its functions. The fluidity of a membrane is crucial to its function. In caribou, circulation is reduced in the lower legs to prevent excess heat loss during cold winters. The membranes of the lower legs have more unsaturated fatty acids than those of the upper legs to retain more fluidity in reduced temperatures. Brain cell membranes in ground squirrels become more solid during hibernation. Phospholipids containing more polyunsaturated fatty acids are more fluid than those with fewer
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This note was uploaded on 01/06/2012 for the course BIOLOGY 106 taught by Professor Rosemaryrichardson during the Fall '08 term at Bellevue College.

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Membranes160 - Membrane Structure and Function - 1 The Cell...

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