Lipids biological polynucleotides

MISCELLANEOUS COMPOUNDS (including biologically useful reagents, low-molecular-weight bioactive substances, antibiotics, coenzymes, vitamins, lipids, phospholipids, nucleosides, nucleotides and polynucleotides)... 

From these and many other studies there was by 1950 plenty of evidence pointing to the possible importance of liquid crystals in tissue. Since then the subject has been explored by direct and experimental methods. My purpose is to examine the chemical forms in which liquid crystals occur and to identify more closely their precise structure and integration into protoplasm and biological fluids. This is often a matter of great difficulty for obvious technical reasons. My own work in this respect has been concerned mainly with lipids and lipoproteins, so I shall refer mainly to these though several other important classes of substances, especially certain proteins and polynucleotides, can exist in the liquid crystalline state and may be present as such in living tissue. 

These molecules — proteins, polynucleotides, polysaccharides, lipids — are not necessarily any different from molecules we study in other branches of chemistry. However, there are some additional factors, arising from their biological origin, that we need to be aware of ... 

Some polymers such as poly(acrylic acid) or polyacrylamide precipitate from aqueous solutions when cooled (normal solubility behavior) whereas others such as poly(ethylene oxide), poly(propylene oxide), or poly(methacrylic acid) phase separate when heated (inverse solubility behavior). Solution turbidimetiy is often used to obtain plots of phase-separation temperatures termed cloud point vs concentration for fixed solvent conditions. Changes in ionic strength, molecular weight, and addition of co-solvents or structure breakers affect the shapes of phase behavior curves. The important conclusion of such studies is that the total free energy of the polymer and water must be considered to predict phase behavior. The structin-e and dynamics of water surroimding polynucleotides, proteins, polysaccharides, and lipids are also major determinants of biological activity (8-10). 

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