Structural View of Biology
Structures in the PDB reveal how cells use chemical energy, light energy, electrical energy and mechanical energy to power the processes of life. Cells must continually interconvert different forms of energy. Energy is obtained from many sources, including light and food. Molecular machines then use this energy to build new molecules, to power motion, to transport molecules to the proper place, to generate heat and light, and to regulate all of the processes occurring in the cell.
Cells build molecular motors that walk and rotate. Molecular motors are used to move things ranging from individual molecules to entire organisms.
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ATP synthase is one of the wonders of the molecular world. ATP synthase is an enzyme, a molecular motor, an ion pump, and another molecular motor all wrapped together in one amazing nanoscale machine. It plays an indispensable role in our cells, building most of the ATP that powers our cellular processes. The mechanism by which it performs this task is a real surprise.
Our cells rely on three main types of motors to move things around, all powered by ATP. Myosin moves along filaments of actin, and is the engine that powers muscle contraction as well as many more molecule-sized transport tasks inside the cell. Kinesin and dynein move along microtubules, in most cases transporting their cargo in opposite directions along the tubule. Together, these tiny molecular motors make sure that everything is in the right place at the right time.
Because cells are so tiny, many cellular processes use simple random diffusion to get materials from one place to another. For instance, when a molecule of glucose is broken down in glycolysis, the ten enzymes and all the intermediate pieces are thrown together in the cytoplasm, and by randomly bumping around, everything manages to find its proper place. For small molecules and proteins, random diffusion is fast enough to get the job done, but for some larger tasks, cells have to take a more active approach. This is where molecular motors come in. Cells make a variety of motors that drag large cellular objects to their proper destinations.
All of the different movements that you are making right now--your fingers on the computer keys, the scanning of your eyes across the screen, the isometric contraction of muscles in your back and abdomen that allow you to sit comfortably--are powered by myosin. Myosin is a molecule-sized muscle that uses chemical energy to perform a deliberate motion. Myosin captures a molecule of ATP, the molecule used to transfer energy in cells, and breaks it, using the energy to perform a "power stroke." For all of your voluntary motions, when you flex your biceps or blink your eyes, and for all of your involuntary motions, each time your heart beats, myosin is providing the power.
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