2 - The molecules of life – an idiot’s guide

Summary

MOLECULE, n. The ultimate, indivisible unit of matter. It is distinguished from the corpuscle, also the ultimate, indivisible unit of matter, by a closer resemblance to the atom, also the ultimate, indivisible unit of matter. Three great scientific theories of the structure of the universe are the molecular, the corpuscular and the atomic. A fourth affirms, with Haeckel, the condensation or precipitation of matter from ether – whose existence is proved by the condensation or precipitation. The present trend of scientific thought is toward the theory of ions. The ion differs from the molecule, the corpuscle and the atom in that it is an ion. A fifth theory is held by idiots, but it is doubtful if they know any more about the matter than the others.

(The Collected Works of Ambrose Bierce (1911), Vol. 7, The Devil’s Dictionary, pp. 220–221)

GENERAL IDEA

Here we outline some of the key concepts and terminology in cell and molecular biology to orientate readers from a more physical science background.

Introduction

The classical biological view is that living organims are typically structured in a hierarchical manner in terms of physiological function relating to length scale. For example, a complex multi-cellular organism is composed of smaller units called organs which appear to be dedicated primarily to a subset of biological processes, and these may be further deconstructed into different tissues, and these tissues may be further sub-divided into smaller structural features consisting ultimately of individual cells, or some structural matrix secreted by cells. Single cells, whether part of a multi-cellular organism as in the human body or simply the organism itself as for unicellular life forms such as bacteria, can in turn be broken up conceptually into smaller subunits. In essence these are structural sub-cellular features which appear to work together to perform a narrow subset of biological functions, for example cell organelles such as the nucleus in certain cell types. Ultimately, smaller sub-cellular feautures can be perceived as collections of single biological molecules.