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Animation: Functions of the Plasma Membrane

by Pearson
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Transport proteins may be carrier proteins that shuttle a molecule, such as glucose, across the membrane by changing shape. Other transport proteins provide channels through which specific molecules or ions, such as sodium, can diffuse. Some transport proteins act as pumps, using the energy of ATP to actively move molecules against their concentration gradient. What other types of functions do membrane proteins perform? Some transfer information. Signaling molecules outside a cell may bind to receptor proteins, which transmit the message into the cell. For example, when insulin binds to receptors on a cell, it signals the cell to take up glucose. Attachment proteins provide support by connecting to the cell's cytoskeleton and to the extracellular matrix. These attachments can also relay information about external and internal conditions. Glycoproteins enable cells to recognize each other. The prefix glycol- refers to short chains of sugar molecules extending from the protein. Other membrane proteins can recognize these ID tags. The sorting of cells within a developing embryo relies on such cell-to-cell recognition. Junction proteins form long-lasting connections between cells. For example, anchoring junctions hold muscle cells together. Tight junctions create a leak-proof barrier between the cells lining the intestine. And finally, some membrane proteins are enzymes, which may be arranged in clusters that carry out sequential reactions. In addition to its plasma membrane, a eukaryotic cell is packed with membranes enclosing a variety of organelles. Looking at these diagrams of an animal cell and plant cell, what might you conclude about the importance of membranes in the life of a eukaryotic cell? These internal membranes share many of the functions of the plasma membrane.
Transport proteins may be carrier proteins that shuttle a molecule, such as glucose, across the membrane by changing shape. Other transport proteins provide channels through which specific molecules or ions, such as sodium, can diffuse. Some transport proteins act as pumps, using the energy of ATP to actively move molecules against their concentration gradient. What other types of functions do membrane proteins perform? Some transfer information. Signaling molecules outside a cell may bind to receptor proteins, which transmit the message into the cell. For example, when insulin binds to receptors on a cell, it signals the cell to take up glucose. Attachment proteins provide support by connecting to the cell's cytoskeleton and to the extracellular matrix. These attachments can also relay information about external and internal conditions. Glycoproteins enable cells to recognize each other. The prefix glycol- refers to short chains of sugar molecules extending from the protein. Other membrane proteins can recognize these ID tags. The sorting of cells within a developing embryo relies on such cell-to-cell recognition. Junction proteins form long-lasting connections between cells. For example, anchoring junctions hold muscle cells together. Tight junctions create a leak-proof barrier between the cells lining the intestine. And finally, some membrane proteins are enzymes, which may be arranged in clusters that carry out sequential reactions. In addition to its plasma membrane, a eukaryotic cell is packed with membranes enclosing a variety of organelles. Looking at these diagrams of an animal cell and plant cell, what might you conclude about the importance of membranes in the life of a eukaryotic cell? These internal membranes share many of the functions of the plasma membrane.