9: Single Molecules Check Access

We rarely get the opportunity to see how individual molecules behave. Mostly what we see are the average effects of large numbers of molecules. Molecular structures determined by crystallographic or NMR methods are time- and number-averages of a large population of molecules. Yet the behaviour of a living cell may be the result of just single molecule interactions; for example, the binding of just one repressor protein to a single DNA site can affect the entire behaviour of the cell. How might we study this? Molecules are always in motion and it is very hard to pin down individuals. This chapter covers some of the methods now being developed to tackle this problem.