Figure 1.

“Feeding without feedback”. In his movie “Modern Times”, Chaplin illustrates the limits of the machine metaphors in biology. (a) A “machine” is supposed to feed the worker without feed-back. (b) The scene showing three workers who, in order to screw in bolts, have to follow the rapid and uncontrollable movement of a conveyor belt illustrates in a suggestive way the difficult task of the three tRNAs (A, P and E) in a "machine" ribosome without any feedback process between the different actors.