It has been a tremendous honour being asked by Keith Wilson, John Walker and Cambridge University Press to take on the role of editorship for this eighth edition of Principles and Techniques. In designing the content, we extend the long and successful tradition of this text to introduce relevant methodologies in the biochemical sciences by uniquely integrating the theories and practices that drive the fields of biology, biotechnology and medicine. Methodologies have improved tremendously over the past ten years and new strategies and protocols that once were just applied by a few pioneering laboratories are now applied routinely, accompanied by ever more fluent boundaries between core disciplines – leading to what is now called the life sciences.

In this eighth edition, all core methodologies covered in the previous edition have been kept and appropriately updated and consolidated. New chapters have been added to address the requirements of today's students and scientists, who operate in a much broader area than did the typical biochemists one or two decades ago. The contents of this text are thus structured into six areas, all of which play pivotal roles in current research: basic principles, biochemistry and molecular biology, biophysical methods, information technology, -omics methods and chemical biology. Of course, due to space restraints that help to keep this text accessible, the addition of new material required us to consolidate and carefully select content to be kept from the previous edition. These decisions have been guided by the over-arching theme of this text, namely to present principles and techniques. Importantly, our experience as teachers has always been that many undergraduates are challenged by quantitative calculations based on these principles, and hence we have continued the tradition of this text by including relevant mathematical and numerical tools as well as examples.

Indeed, new chapters on data processing, visualisation and Python have example applications that can be accessed from the CUP website to aid understanding.

Sadly, two authors of previous editions have passed away: John Fyffe died shortly after the seventh edition was launched and Alastair Aitken passed away in 2014. Also, Keith Wilson, John Walker and Robert Burns decided to retire, and we thus invited several new authors to contribute to this eighth edition.

INTRODUCTION

The term preparative biochemistry describes the purification of biological molecules such as proteins, viruses and nucleic acids to a sufficiently high concentration so as to be useful for a range of processes. Preparative biochemistry can be contrasted with analytical biochemistry that can be summarised as the application of small quantities of analyte to determine the composition or content of the biochemical sample.

At first sight, the purification of one protein from a cell or tissue homogenate that will typically contain 10 000–20 000 different proteins may seem a daunting task. However, in practice, on average, only four different fractionation steps are needed to purify a given protein.

The reason for purifying a protein can be to provide material for structural or functional studies; the final degree of purity required depends on the purpose for which the protein will be used. For some applications, protein samples are not required to be of highest purity, but for pharmaceutical use, the desired purity is typically close to 100%.

Theoretically, a protein is pure when a sample contains only a single protein species, although in practice it is almost impossible to achieve this stage. Fortunately, many studies on proteins can be carried out on samples that contain as much as 5–10% or higher contamination with other proteins. This is an important point, since each purification step necessarily involves loss of some of the protein that is the target of purification. An extra (and potentially unnecessary) purification step that increases the purity of the sample from, say, 90% to 98% may result in a protein sample of higher purity, but insufficient sample material for the planned studies.

For example, a protein sample of 90% purity is sufficient for amino-acid sequence determination studies as long as the sequence is analysed quantitatively to ensure that the deduced sequence does not arise from a contaminant protein. Similarly, immunisation of a rodent to provide spleen cells for monoclonal antibody production (Section 7.2.2) can be carried out with a sample that is considerably less than 50% pure. As long as the protein of interest raises an immune response, the fact that antibodies may also be produced against the contaminating proteins is typically ignored.

FROM BIOCHEMISTRY AND MOLECULAR BIOLOGY TO THE LIFE SCIENCES

Biochemistry is a discipline in the natural sciences that is chiefly concerned with the chemical processes that take place in living organisms. Starting in the 1950s, a new stream evolved from traditional biochemistry, which, until then, mainly investigated bulk behaviour and macroscopic phenomena. This new stream focussed on the molecular basis of biological processes and since it put the biologically important molecules into the spotlight, the term molecular biology was coined. Importantly, molecular biology goes beyond the mere characterisation of molecules. It includes the study of interactions between biologically relevant molecules with the clear goal to reveal insights into functions and processes, such as replication, transcription and translation of genetic material.

Major technological and methodological advances made during the 1980s enabled the development and establishment of several specialised areas in the life sciences. These include structural biology (in particular the determination of three-dimensional structures), genetics (for example DNA sequencing) and proteomics. The refinement and improvement of methodologies, as well as the development of more efficient software (in line with more powerful computing resources), contributed substantially to specialist techniques becoming more accessible to researchers in neighbouring disciplines. What once had been the task of a highly specialised scientist who had been extensively trained in that particular area has consistently been transformed into a routinely applied methodology. These tendencies have pushed the feasibility of cross-disciplinary studies into an entirely new realm, and in many contemporary laboratories and research groups, methods originally at home in different basic disciplines are frequently used next to each other.

It is thus not surprising, that in the past 15–20 years, the term ‘life sciences’ has been used to describe the general nature of studies and research areas of a scientist working on studies related to living organisms.

THE EDUCATION OF LIFE SCIENTISTS

The life sciences embrace different fields of the natural and health sciences, all of which involve the study of living organisms, from microorganisms, plants and animals to human beings. Importantly, even satellite areas that are methodologically rooted outside natural or health sciences, for example bioethics, have become a part of the life sciences.