2.2 Biochemistry and Cell Biology
KEY CONCEPTS
By the end of this section, you will be able to do the following:
- Explain the role of biochemistry in characterizing cell function, helping make the link between cell structure and function
- Evaluate the importance of the discovery of enzymes for cell biology
- Describe techniques that are useful for isolating cellular components, including molecules and organelles, and why these techniques are helpful in biochemistry
At about the same time that cell structure was being explored by microscopists, others were more focused on how cells functioned. What were chloroplasts and mitochondria doing, or the Golgi apparatus for that matter? What were chromosomes made of? How did cells stay alive? In the early 1800s, it was widely believed that living organism had some unique “vital essence” and were not subject to the laws of physics and chemistry. Biochemistry changed that by helping us understand what cells are made of and how they function. In this chapter, we will explore some of the key biochemical discoveries and techniques that helped move cell biology forward.
Enzymes and Biochemical Pathways
At around the same time that Schleiden and Schwann were articulating Cell Theory (Ch 1.1) in the early 1800s, a German chemist named Friedrich Wöhler demonstrated that the biological compound urea (found in urine of humans and many other animals) could be synthesized in the laboratory. This showed that a biological compound could be made from inorganic starting material, contradicting the idea that the “vital essence” of living organisms was somehow unique. This was an important paradigm shift for beginning to understand how the cells within organisms function, because much of that function (we now know) relies on chemical reactions. The field of biochemistry devotes itself to studying chemical reactions (the formation and breakdown of chemicals) in biological systems.
It took about another century to start understanding the importance of enzymes – proteins that help these chemical reactions occur in cells. Much of the early work to discover enzymes was done in yeast – single-celled fungal cells. In the late 1950s, Louis Pasteur showed that living yeast cells converted sugar into ethanol – a fact we still use to this day when making beer and wine (Figure 2.9). Another 40 years later, Eduard and Hans Buchner showed that fermentation could take place after yeast cells were broken open, but their contents were still active. The active agents from these yeast cells eventually became known as enzymes (“zyme” = yeast in Greek). We will learn more about enzymes in Chapter 6.4
Most chemical transformations in cells require multiple steps. The example of alcohol fermentation in Figure 2.9 is a relatively short and simple pathway. In the early- to mid-1900s, various scientists started working out the individual steps in long and complex biochemical pathways. In the 1920s and 1930s, work by Fritz Lipmann showed that adeno