Dan Levitt in Time:
Our cells, each composed of 100 trillion atoms made of particles from the Big Bang, are filled with all kinds of structures. These include organelles—little factories like energy-producing mitochondria—and tiny molecular machines like ATP synthase, whose rotor and shaft spin at up to 300 rpm to produce ATP, the molecules that transmit energy in our cells. The interior of our cells are also filled with all kinds of molecules randomly colliding at tremendous speeds. Water molecules, for example, zigzag at the astonishing speed of over 1 thousand miles an hour (although they only go about 4 billionths of an inch before they smack into another molecule). In addition to collisions, cells face a myriad of other threats from within and without. You might expect them to suffer the same fate as our cars and dishwashers and constantly break down. But they don’t. Your body has an ingenious three-part strategy to keep you out of the junkyard.
The biophysicist Dan Kirschner told me that just thinking about everything that could go wrong in cells used to keep him awake at night. He was learning about cell development in a graduate school course just as his wife was about to have a baby. He was so overwhelmed by the many opportunities for mistakes that he feared his daughter would be born with a neck like a giraffe.
More here.