Applications of physical techniques to studies of membrane structure have increased greatly in the past few years and they have begun to provide more precise structural parameters for membranes and also some indication of the physical states of the molecular constituents in the membranes. Direct measurements of membrane features have been made by electron microscopy and by X-ray diffraction methods. Spectroscopic techniques especially infrared absorption, nuclear magnetic resonance absorption and optical rotatory dispersion and circular dichroism measurements have provided additional data relating to the physical states of the molecular components in the membranes.

The initial act for visual perception is the absorption of light in the photo-pigment of the receptor end-organs. Since both light and the nervous message have a quantal structure, any theory of visual information processing should in principle be a digital processing theory. And not only in principle, since we know for certain that in many situations the number of quanta is rather restricted, so that an over-all thermodynamic theory cannot but fail to adequately describe visual facts.

Like DNA and the various forms of RNA, a protein molecule is an information storage system. It contains in fact one or more polypeptide chains which may be regarded as linear sequences of twenty different types of monomer units. It is now clearly established that the chemical information corresponding to a given sequence of a polypeptide chain, containing n amino acid residues, is stored in a segment of one of the two strands of DNA containing 3n nucleotides. The transfer of such information from a gene to a polypeptide chain takes place according to the well-known process involving a transcription and a chemical translation step. This last step leads to a polymer which, in appropriate conditions, takes a three-dimensional conformation or tertiary structure which should correspond to a free-energy minimum of the molecule and its surrounding water solution.