Condensation nuclei necessary

In Robinson s now well-known suggestions, regarding the processes by which alkaloids may be produced in plants, two main reactions are used j the aldol condensation and the similar condensation of carbinol-amines, resulting from the combination of an aldehyde or ketone with ammonia or an amine, and containing the group. C(OH). N., with substances in which the group, CH. CO. is present. By these reactions it is possible to form the alkaloid skeleton, and the further necessary changes postulated include oxidations or reductions and elimination of water for the formation of an aromatic nucleus or of an ethylene derivative. 

This reaction furnishes the best means of preparation of hundreds of cyclic olefinic compounds, most of which are beyond the scope of this book. In its simplest form, the reaction may be looked upon as a 1,4-addition of an olefinic compound to a conjugated diene. The scope of the reaction is inadequately tepiresented by the above equation. The diene system may be a part of an aromatic or heterocyclic nucleus such as a-vinylnaphthalene or furan, or the double bonds may be parts of two independent molecules. The olefinic compound (dienophile) usually contains one or mote groups (Z) which activate the double bond, although this is not necessary e.g., ethylene is condensed with butadiene at 200° to give cyclohexene (18%). Triple bonds may replace double bonds in both the diene and dienophile. Excellent reviews of the reaction have been published. Cis addition of the dienophile to the diene occurs, and several of the reactions have been shown to be truly reversible. Butadiene is conveniently prepared in the laboratory by passing the vapors of cyclohexene over a hot filament. ... 

Thus, in addition to the intact basic ring structure of the ABC system, one has attained both regioisomeric differentiation of the phenol necessary for the vonPech-mann condensation, and provision for the vinyl ether insertion in the form of the C-15 hydroxyl (or a possible derivative thereof). Indeed, it is evident that any of several directions may be taken in this route by variations in (a) the nature of the functional groups on the phloroglucinol nucleus and C-15 hydroxyl, (b) the timing of their introduction and removal and, (c) the timing for the introduction of the vinyl ether moiety. 

At the end of the S period, the cell enters in the G2 period. It is believed that condensation of chromosomes occurs as a result of synthesis of a number of uncharacterized factors as the cell enters the D phase from the G2 phase. This is the beginning of the prophase of mitosis. The HeLa cell in mitosis can cause premature chromosome condensation (chromosomal pulverization) of an interphase nucleus that enters the cell by cell fusion (Johnson and Rao, 1970 Matsui et al., 1972). The chromosomal condensation factor is not species specific (Johnson et al., 1970). Arrest of the G2 phase may occur but usually involves only a few percent of the cells. It has been studied best in the mouse ear epidermis (Gelfant, 1963). Cyclic AMP may mediate the reversible arrest of cells in the G2 phase (Nose and Katsuta, 1975 Willingham et al., 1972). Fusion of a HeLa cell in the G2 phase with a cell in an earlier phase can arrest the G2 phase and prevent progression into the D phase (Rao et al., 1975 Rao and Johnson, 1970). Protein synthesis is necessary until 10 min before prophase in order for cells to enter into mitosis (Tobey et al., 1966). RNA synthesis is also required but is completed before the protein synthesis requirement (Tobey et al., 1966). 

DNA is an extremely large molecule. The chromatin of a typical human chromosome would be about 1 mm in length if it were extended and would therefore span the nucleus more than 100 times . In its normal state it is condensed by various cellular proteins, such as the histone proteins, that allow such a large molecule to fit inside the cell nucleus. Even a plasmid DNA molecule of around 6 kb in size has an extended stmcture several hundred nanometers in diameter. In order to efficiently deliver plasmid DNA into cells it is necessary to condense them to a much smaller size. 

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