Generally, proteins are best studied in pure form. The great enzymologist Efraim Racker once said “Don’t waste clean thinking on dirty enzymes”. It is a central concept of much molecular biology that living processes can be broken down into individual steps that are much easier to study than entire processes. This means that studying the properties of individual proteins can help us to understand the processes in which they participate. Examples of the kinds of studies that can be done with purified or partially purified proteins are many (some are listed below) and, while some of these studies were possible long before molecular biology came along, cloning techniques have greatly enhanced our ability to study and understand proteins. This is mostly because we can now express and purify them in high quantities in organisms which are easily grown in the laboratory.