Lesson #15 of 18 in the Brain Makeover collaboration with Professor James Trefil/George Mason University, the 76ers Cheerleaders and the Science Cheerleader. See Brain Makeover Series.
All living things are made from cells, the chemical factories of life.

One of the most important discoveries of nineteenth century science was that life is based on chemical reactions, and that these reactions take place in complex structures called cells. In the twentieth century we learned that the instructions for carrying that chemistry are carried in DNA.
The best analogy for a cell is a complex factory—think of a big refinery. There is a front office where instructions for carrying out the factory’s activities are kept. DNA in the nucleus of cells plays this role. In a factory there is a place where energy is generated. In cells, this happens when complex molecules are combined with oxygen in organelles called mitochondria. There is a wall that separates the factory from its surroundings, and in a cell there is a flexible cell membrane that carries out this function. There must also be a way for material to enter and leave the factory, a function that in the cell is the job of large protein molecules called receptors in the cell membrane. The shape of these membranes matches that of molecules outside the cell.
The chemical reactions in a cell are run by protein molecules that serve as enzymes, and the information for building those molecules is coded in stretches of DNA called genes. Understanding how genes operate remains a major area of research in the sciences.
(Image credit.)

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