Biochemists study biochemistry, which is the chemistry of living organisms.
* To go a little further back in history: biochemistry is a relatively new science.*
In former times, "organic" chemistry was thought to be the chemistry of living organisms, and exclusively possible within living organisms up to the time when the German chemist Friedrich Whler managed to synthesize an "organic" compound, urea, in the laboratory (1828). Nowadays, the distinction is made between
- organic chemistry (now defined as chemistry of compounds containing the element carbon)
- inorganic chemistry (of compounds not containing carbon) and
- biochemistry (chemistry of living organisms).
The major constituents of living organisms do contain carbon, but the term bio-chemistry now refers to the exact chemical reactions how they occur inside the organism, notwithstanding the fact that some of them can also be reproduced in the test tube.
* Biochemistry is a fascinating science:*
The periodic table contains around 120 elements, but only 6 of them (H, C, N, O, P and S) constitute the major classes of biochemical molecules: nucleic acids, proteins, lipids and carbohydrates. In addition to these elements, others are needed in smaller amounts to assure a proper function of the organism. These are known as minerals (like, for example, Ca) and trace elements (needed in extremely small amounts, such as Se). Chemical reactions and interactions between this small group of elements finally results in the astounding phenomenon that we know as "life"!
* So if you read a biochemistry book, what do you learn? *
You read how the above-mentioned classes of molecules are made and what they do.
1. Proteins: They are made from amino acids, using a system of enzymes that can decipher the genetic code. The question what they do opens a large box of answers: They work as enzymes, as transporters, as ion channels, as signal transducers, as hormones, and so on.
2. Nucleic acids: They are made from nucleotides (and these from sugars, inorganic phosphate, and small organic basic molecules). Desoxyribonucleic acid (DNA) constitutes the genetic code, and ribonucleic acid (RNA) provides a means to translate it into proteins.
3. Lipids: They can be made from breakdown-products of sugars. Some lipids are part of cell membranes, some serve as energy reservoir, some as hormones.
4. Carbohydrates: Can be made "from the scratch" (from carbon dioxide) by plants in the process of photosynthesis. These astounding organisms literally can live on air, water and sunlight! Animals take up carbohydrates by eating plants, and if needed they can make them themselves, but only from breakdown-products of amino acids. (By the way, they cannot make them from lipids! So if you are on an extreme diet, not the fat helps restore the energy reservoirs, but the proteins.) The controlled degradation of carbohydrates is the most important process of which the cells derive their energy. Furthermore, single units of carbohydrates can be connected to form chains, which serve for example as structural elements or as long-term energy reservoir.
These explanations can only give an overview. They miss, for example, the role of vitamins (compounds that are indispensable for life but can NOT be produced by the organism itself and have to be taken in from outside). They also miss to explain the role of inorganic elements, and the multiple interactions and connections between all these groups of molecules.
* Biochemists try to understand life from the scratch.*
Biochemistry is exactly this: It starts with the elements, with chemistry, and connects it to biology.
How is an amino acid made from its elements? How is a protein made from amino acids? What does this protein do? Which function does it fulfil in the organism and how does it interact with other molecules? Somebody doing pure biochemical research would study metabolic pathways (such as the synthesis or degradation of biomolecules) or the structure and modifications of biomolecules.
But this is not the end point, and many basic questions being solved, biochemists nowadays go many steps further. Understanding biology in such detail can help to solve very important questions, such as: What happens if the function of a certain protein is disturbed? (This could mean disease such as cancer, diabetes or Alzheimer's disease.) Can the function of a protein be inhibited or enhanced? (This could be a possible cure.) Just an example!
But can we ever understand life? I remember a joke about a man who wanted to know about the important and frequently discussed ethical question "when does human life start"? He asked a biochemist who should really know what is life. And he said: "Human life starts when the children have grown up and left home, and the dog has died." Not a stupid answer! I think there are questions that science cannot answer.