Comparative biochemistry can be a vague concept with multiple meanings, though it can reveal fascinating interactions between organisms and their biologies. At the very least, scientists call it an interdisciplinary field of science that seeks to gain insight into unanswered questions by finding connections between seemingly unrelated topics. In practice, it is most commonly understood as either the study of evolutionary relationships between organisms and how those relationships shed light on deeper questions of how biological life forms function.
TL;DR (Too Long; Didn't Read)
An interdisciplinary study, comparative biochemistry aims to bridge the gap between disparate fields in science. Most commonly, it refers to the study of how life forms live, and how their constituent pieces, down to a cellular level, work.
An Integrated Field of Study
The University of California at Berkeley has a graduate program called Comparative Biochemistry. Its faculty members come from diverse fields of science, including molecular biology, cell biology, chemistry, plant biology, nutrition and public health. This diversity attests to the broad scope of comparative biochemistry as a discipline. It also underscores the commonalities that pervade these fields of study, indicating that seemingly disparate fields may actually provide insight for solving problems addressed by individual fields. Journals also exist under the name of comparative biochemistry, and the scope of their publications further underscores the theme of interdisciplinary scholarship.
A common definition of comparative biochemistry is the study of evolutionary relationships between organisms. All living organisms share a common genetic code in the form of DNA, which provides information for making the protein machines that do the day-to-day work of cells. Comparative biochemistry studies protein machines and enzymes, but both are encoded by DNA sequences. By comparing similarities and differences in these genes, scientists can piece together evolutionary relationships between organisms. The purpose of this is to better understand the history of life, but to also find animal research models that may shed light on human disease.
Comparing Related Genes
Different species of organisms may contain the same genes, but with slightly or very different sequences. These genes may do similar things in each organism, or they may do very different things. This happens because of the differences in their DNA sequences, which manifest as similar proteins with slightly different three-dimensional shapes, and thus different functions. The advantage of studying similar genes in two species is that the structure and function of a gene in one species often gives insight into its role in the other species.
Just as one gene in an organism can help a scientist understand a similar gene in another organism, insights can be gleaned through comparative biochemistry about the level of interaction of many proteins. Proteins often form complexes, or clusters of proteins, with their partner proteins when doing their job. Learning who interacts with whom in one species to complete a cellular function helps a scientist to guess the interacting partners for a certain gene in another species. This approach helps scientists make educated guesses as to which unknown proteins are yet to be identified as partners in other species.