Poster Biochem - L iving cells are filled with complex...

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OUTSIDE THE CELL Some molecular machines perform their jobs outside of cells. Many are compact, so that they can diffuse quickly to their site of action. This is true of the four hor- mones shown at the top: insulin and glucagon, which together regulate blood sugar lev- els, interferon, which carries signals in the immune system, and human growth hor- mone. The seven digestive enzymes (in yellow) are also small and very stable, so that they can survive the hostile environment in the digestive tract. Each of these enzymes has a small groove (oriented towards the top in each) that binds to a different target molecule and digests it. At the bottom is rhinovirus, the virus that causes the common cold, and an antibody, our major defense against viruses. Antibodies bind to viruses and prevent them from binding to cell surfaces, thus blocking infection. 1 CHEMICAL FACTORIES Cells build a bewildering variety of enzymes—proteins that perform chemical reactions. At the top are the ten enzymes that perform glycolysis, the breakdown of sugar to form ATP. Below that are several enzymes that perform different housekeeping reactions. Dihydrofolate reductase activates a key cofactor molecule and alcohol dehydrogenase breaks down alcohol. Ribulose bisphosphate carboxy- lase/oxygenase is the most common enzyme on the Earth, and performs a key step in the capture of carbon dioxide by plants to form sugar. The three synthases and the transferase make different building blocks for creating new molecules. Nitrogenase performs an essential role in the ecosystem by converting nitrogen gas into a form that living cells can use. 4 TRANSPORT AND STORAGE Of course, a perfectly sealed membrane would be of little use to cells, because nutrients could not get in and wastes could not get out. The box shows a membrane looking face-on. Five proteins that form channels through the membrane are shown. To the right of the box are several soluble proteins involved in transport and storage of molecules. Hemoglobin and myoglobin carry oxygen. Ferritin forms a hol- low shell that stores iron ions. Serum albumin carries many different molecules in the blood. 3 BUILDING NEW PROTEINS New proteins are built by ribosomes—complex molecular factories that read the genetic code and use it to direct construction. Many molecular machines are needed to assist the process. Twenty different aminoacyl-tRNA synthases (six are shown here) load the building blocks onto tRNA, ready to be added to a growing protein chain. Several protein factors, shown below the ribosome, guide each tRNA into the proper spot. The three chaperone pro- teins shown at the bottom help each new protein fold into its proper shape. 6
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This note was uploaded on 02/07/2011 for the course BCMD 3100 taught by Professor Rose during the Spring '11 term at University of Georgia Athens.

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