Condensed form, organic structures

Carbonyl condensation reactions occur with great facility over zeolite catalysts (26, 62, 63). From the organic structural standpoint, the common feature—and usually the primary event—is the attack of a nucleophile. A, on the positive end of the dipole of a C=0 bond, forming a new C—A bond and a hydroxyl group. In Equation 9, the carbonyl... 

The reactions are analogous to the one by which methane is made from methyl iodide and the zinc-copper couple. In the case of these iodides, however, zinc alone is capable of bringing about the reaction. Such formulas as the above are usually written, for convenience, in a more condensed form. In the molecule represented by the formula (1) there is one carbon atom to which are joined three methyl groups and an iodine atom. This fact is shown by the formula (CH3)3CI. Formula (2) can be written (CH3)2CH.CH2l. It is important that the student should understand clearly the significance of these condensed formulas, as such formulas are generally used to express the structure of organic compounds. 

The main protein component of chromatin is histones, which are basic proteins associated with the DNA in the form of structures called nucleosomes (Fig. 6.3) (12). The DNA can be stored in very small, compact forms called condensed DNA, which is 10 - to 106-fold less in volume than uncondensed DNA. The main force that must be overcome in the condensation process is charge repulsion because of the negatively charged phosphates in the polyanion. This repulsion may be overcome by DNA interaction with multivalent organic and inorganic cations. The histones, which are the major components of the nucleosome, are cationic organic proteins that interact with DNA in the compact nucleosome structure. 

The survey of physical chemistry has revealed the existence of a whole hierarchy of structure and patterns, those of the nuclear components, those of the electrons in the atom, of the atoms in molecules, and of atoms, molecules, and electrons in all the varied gaseous and condensed forms of matter as we ordinarily know it. But this is not the end. Rocks and mountains, lakes and rivers, winds and snowstorms are large-scale versions of things which might exist in test-tubes, but the world of living organisms is of a different kind. It is ordered, it is differentiated, it grows and reproduces itself, it is purposive it adapts itself and it evolves. Einally it becomes the seat of consciousness. 

Other forms of DNA such as the compacted O form have also been described [33, 34]. This form occurs in association with positively charged proteins or polypeptides such as histones. A pertinent point here is that in nuclei of eukaryotic cells, DNA does not occur unassociated as in bacteria. Instead, it is present in the highly condensed form of chromatin this essentially consists of periodic aggregates of histone proteins that package the DNA helix into particles called nucleosomes, which are considered to be the primary level of structural organization within the chromatin fibrils [35]. 

---