Biochemistry is the study of the chemistry of the living world. Biochemists study organisms at the molecular level in order to understand how they carry out life processes. In laboratory experiments, the biochemist separates substances isolated from living cells and determines their chemical structures and properties. Then these substances are put back together under controlled conditions to find out how they interact.
What does all this mean? Let's illustrate by example. The fermentation process by which sugar from cellulosic plant wastes is chemically changed into alcohol underlies the production of gasohol. Yet the fermentation of sugars in fruit juice is one of the oldest cottage industries, having been practiced long before the word "biochemistry" ever existed. The origins of biochemistry lie in the study of these fermentation processes.
Louis Pasteur discovered that transformation of sugar to alcohol is caused by a living organism, yeast. Eduard Buchner later expanded upon that conclusion by grinding up yeast cells and extracting a water-soluble, cell-free "juice" that could ferment sugar to alcohol in the absence of living cells. Pasteur had done a biology experiment. He showed that fermentation was a life process that occurred in a living organism. Buchner had done a biochemistry experiment. He showed that living cells could be taken apart. A mixture of dissolved substances, lifeless molecules, could still carry out the "life process" of fermentation.
Biochemists study how living organisms extract food and energy from their environment and how they use the extracted molecules to make more of themselves. Buchner, by taking apart yeast cells, had opened the way to ask biochemical questions like: What kinds of molecules cause fermentation? How many different molecules are necessary? Why does the yeast cell undertake the process of fermentation? Why does fermentation only happen if you keep oxygen out? These are questions that can be answered by separating the "dissolved substances" in the "juice" and asking what they are, how they interact with each other, and how their properties are related to their chemical nature.
By using this type of investigative approach, biochemists have discovered that...
Although too much cholesterol can cause heart disease, our bodies make cholesterol because it is an essential component of the membranes of our cells.
Cells distinctively mark themselves by putting specific groups of sugars, linked together in recognizable patterns, on their surfaces. Your body will reject transplanted tissue if the cells of that tissue have the wrong pattern of sugar groups on their surfaces.
One of the reasons plants require the mineral nutrient magnesium is because it forms part of the structure of chlorophyll, the molecule plants use to trap solar energy.
Penicillin kills bacteria by preventing them from putting together the chemical structure of their cell walls.
The molecular modification of chromatin that comprises the "epigenetic code" contributes to differentiation of embyronic stem cells and supression of tumor formation.