Biochemistry

Proteins, enzymes, DNA, and the molecular chemistry of life

What is biochemistry?

Biochemistry is the chemistry of living things — it studies the molecules that make up cells and the chemical reactions that keep organisms alive, from the smallest bacterium to the human body.

The major molecules of life

Living things are built from a few major classes of large molecules. Proteins, made from chains of smaller building blocks called amino acids, do most of the actual work inside a cell — some form structural material, others (enzymes) speed up chemical reactions, and others carry signals or transport materials. Carbohydrates (sugars and starches) provide and store energy. Fats (lipids) also store energy and form the membranes that enclose every cell. DNA and RNA carry and use the genetic information that tells a cell how to build all the others.

Enzymes: nature's chemical accelerators

Most chemical reactions inside a living cell would be far too slow to sustain life without help. Enzymes are proteins that dramatically speed up specific chemical reactions (a specialized form of the catalysis introduced in the Physical Chemistry article), often by factors of a million or more, while remaining highly selective about exactly which reaction they speed up.

Metabolism: how cells get and use energy

Metabolism is the sum of all the chemical reactions happening inside a cell, generally divided into two categories: breaking larger molecules down to release energy (catabolism, as in digesting food) and building larger molecules using that energy (anabolism, as in growth and repair). A cell captures usable energy from these reactions primarily in a molecule called ATP, which acts as a kind of universal, portable energy currency used throughout the cell.

Why biochemistry matters

Biochemistry explains, at the molecular level, how the human body actually works — digestion, muscle contraction, immune response, and much more — and it underlies the development of most modern medicines, since understanding a disease's biochemistry is usually the first step toward treating it.