Within the living cell are molecular machines, tiny component parts that are precisely formed to carry out very specific tasks in living cells. Most molecular machines are made up of several component proteins all of which must fit perfectly together in order to work. It is like the key you use to unlock the door to your house. The key must fit the lock exactly in order to work. If the key is the wrong shape however, it will not fit the lock and you will not get into the house. Or suppose you have a box of parts for a new bicycle, but when you try to assemble the bicycle, you find that the parts don’t fit together. If the parts do not fit together, the bicycle does not work. In the case of molecular machine (the word molecular refers to the fact that the machines are extremely microscopic) they are made up of proteins that have to fold into a precise shape in order to work. DNA code (information) determines which proteins are made and how. Without the correct DNA code in the cell, functioning molecular machines could not exist.

Molecular machines therefore carry out precise functions necessary for the cell to survive. There are many molecular machines in cells. All are irreducibly complex in that all the component parts must be present at the same time and all have to fit precisely in order for the machine to function.  The bacterial flagellum is a very famous example of a molecular machine. Other examples are the six different types of secretion systems:  T6SS, T5SS, T4SS, T3SS, T2SS and T1SS. These tiny syringe-like structures inject poisons or hostile DNA or RNA into the cells of victims. Then there is ATP synthetase which forces a phosphate ion onto adenosine diphosphate to form a molecule with high chemical energy content. Kinesin in the eukaryotic cell carries large loads along microtubules, and the eukaryotic flagellum are still other examples of molecular machines. In addition to these, there is DNA polymerase, and RNA polymerase and their associated proteins which manage the replication of DNA and the copying of its information.

Related Resources

• The Workhorse of the Cell: Kinesin (YouTube, 3 min)
• Molecular Machines – ATP Synthase: The power plant of the cell (YouTube, 3 min)