Abstract: Abstract Deoxyribonucleic acid (DNA), the biological molecule that determines the evolutionary architecture of all known life forms has been largely ignored as regards its own evolution from the prokaryotic cell (cells without nuclear membranes), to the eukaryotic cell (cells with nuclear membranes). In addition, the properties of prokaryotic DNA, have in some cases, been imposed on eukaryotic DNA resulting in the loss of evolutionary continuity of DNA. Regardless of the source of DNA, only small sections are usually examined as a salt extract. It is devoid of its associated proteins, which in the eukaryotic cell are responsible for the packing of DNA into chromosomes, and from its intimate connections with the nuclear membrane. From such studies various structures for DNA have been proposed which have not found general acceptance. Thus, any hypothesis on the structure of DNA must be able to incorporate most, if not all, other reported structures. Similarly, any structure proposed for DNA must be considered in terms of its own evolution as distinct from its phenotypic evolutionary expression. A single strand of DNA has opposite terminal ends, a 3′OH group and a 5′ phosphate group. These ends may join by a 5′ - 3′ phosphate linkage forming circular DNA. Both these single stranded linear and circular forms of DNA are considered to belong to primitive prokaryotic cells. A higher order of circular prokaryotic DNA may be formed if at one end, a single strand of DNA is turned through 180°, resulting in the 3−OH and 5′ phosphate groups being diagonally opposite each other (3′5′). This circular DNA has a continuous phosphate backbone and a discontinuous base sequence, Mobius circular DNA. The discontinuous base sequence may provide a start/stop signal for DNA and RNA polymerase. This Mobius DNA (M. 1.) may give rise to single circular, double linear or double circular DNA. During the replication of M. 1. DNA it may be possible for the two complementary strands to form one continuous Mobius DNa circle (M. 2. DNA) by two 5′3′ phosphate linkages. Thus, there are two start/stop signals for DNA and RNA polymerase, therefore DNA replication would occur as two separate strands and require splicing together. In addition, M. 2. DNA may be the first example of gene duplication and represent the first primitive eukaryotic DNA. Another form of Mobius DNA may be derived from M. 1., which represents the higher order in eukaryotic cells. This may be formed by two complementary strands of M. 1. forming a Mobius DNA circle (M. 3. DNA) by 5′ - 3′ and 5′3′ phosphate linkages. This will result in a double right handed α helical configuration which can be formed into a linear side-by-side configuration with a double loop at one end, which is a left handed helix. The side-by-side configuration allows base pairing, but in the double loop, the bases are facing in the same direction and are displaced, therefore they cannot base pair. Thus, single stranded DNA is existing with based paired DNA. It is proposed that the single stranded DNA represents unique copy and the base paired DNA repetitive copy, and that a number of these M. 3. DNA's constitute a gene. The DNA of eukaryotic cells is wound around a number of histone cores. Between each core there is a linking region of DNA upon which the histone H1 is attached. The core plus linker, represents a nucleosome, and under the electronmicroscope resembles beads on a string. A number of configurations have been proposed for these core histones which enable DNA to be packed to form chromosomes. The various configurations proposed for the histones can be achieved by considering each histone as a Mobius circle. The association of these Mobius histones results in the formation of cores in the form of wedge-shaped cylinders, which associate to form an helical spring-like solenoid with a central hole, when M. 3. DNA undergoes compaction.
Publication Year: 1981
Publication Date: 1981-03-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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