China
Africa
Explore chapters and articles related to this topic
The Biosphere
Published in Stanley E. Manahan, Environmental Chemistry, 2022
Molecules of DNA are huge, with molecular masses greater than 1 billion. Molecules of RNA are also quite large. The structure of DNA is that of the famed “double helix” (Figure 21.13). It was figured out in 1953 by James D. Watson, an American scientist, and Francis Crick, a British scientist, aided by structural data from X-ray crystallographer Rosalind Franklin. Watson and Crick received the Nobel Prize for this scientific milestone in 1962. This model visualizes DNA as a so-called double α-helix structure of oppositely wound polymeric strands held together by hydrogen bonds between opposing pyrimidine and purine groups. As a result, DNA has both a primary and a secondary structure; the former is attributed to the sequence of nucleotides (each distinguished by the nitrogenous base in its structure) in the individual strands of DNA and the latter results from the α-helix interaction of the two strands. In the secondary structure of DNA, only cytosine can be opposite guanine and only thymine can be opposite adenine, and vice versa. Basically, the structure of DNA is that of two spiral ribbons “counter-wound” around each other as illustrated in Figure 21.13. The two strands of DNA are complementary. This means that a particular portion of one strand fits like a key in a lock with the corresponding portion of another strand. If the two strands are pulled apart, each manufactures a new complementary strand, so that two copies of the original double helix result. This occurs during cell reproduction.
Helical Symmetry
Published in Mihai V. Putz, New Frontiers in Nanochemistry, 2020
The functionality of various hierarchically structured materials, like solids, biomolecules or supramolecular assemblies is assured by the particular geometry arrangement of their building blocks (Chung et al., 2011). They possess in many cases highly ordered microscopic structures, like crystals (Hoddeson et al., 1992), co-crystals (Braga et al., 2009), dendrimers (Buhleier et al., 1978; Yates et al., 2005) or coiled peptide chains (Pauling et al., 1951) which often exhibit periodic structures by repeating itself in different directions in the space. The discovery in 1953 of the double helix structure of the DNA by James Watson and Francis Crick (Watson et al., 1953) is considered as the starting point of the modern molecular biology. The functionality of biomolecular structures is given by their three-dimensional shapes, therefore knowing their specific physicochemical properties we can elucidate how these specific functionalities are related to the structure of biomolecules.
Toward Understanding the Intelligent Properties of Biological Macromolecules
Published in George K. Knopf, Amarjeet S. Bassi, Smart Biosensor Technology, 2018
The DNA double helix is a regular repeating 3-D structure comprising two right-handed interwound polynucleotide single strands. Each single strand contains a linear string of nitrogenous bases that form complementary hydrogen bonds to the corresponding bases on the opposite single strand. Together, these bases create the A-T and C-G base pairs making up the central core of the double helix. At the time of the original publication by Watson and Crick of the fiber diffraction–based 3-D structure of DNA, and for the following two decades, little structural variability was imagined for the DNA double helix. However, we know today, primarily from numerous determinations of 3-D structures for short DNAs by NMR and x-ray crystallography, that DNA forms a variety of repeating secondary structure types, some of which are interconvertable. We also know that DNA, while still considered an overall rigid structure on the length scale of tens of base pairs and with a persistence length in solution on the order of <200 bp, is known to be capable of considerable generic as well as sequence-based variation in structure and dynamic motion (109,110). The sequence-based properties and dynamics of the DNA double helix underlie its intelligent properties. For emphasis in the discussion that follows, we have italicized the individual intelligent properties of DNA as we discuss them.
Heredity under the Microscope: Chromosomes and the Study of the Human Genome
Published in Annals of Science, 2021
The first time I asked one of the pioneers of medical genetics about the impact of the DNA double helix on their field and he replied, ‘Basically, none’, I was stunned. It was common knowledge that the history of molecular genetics led directly from the double helix, solved in 1953, to the Human Genome Project, with its promise of genetically personalized medicine, announced complete in 2003. But I kept receiving the same answer and eventually the picture clarified. Although the first instance of Mendelian inheritance in humans dates to 1902 – the very origins of genetics as a science – medical genetics, and human genetics more broadly, went nowhere slowly for half a century. While fruit flies, maize, mice, and moulds had their chromosomes stained, counted, and mapped, human chromosomes were just too damned difficult to see and count. In 1953, the biology textbooks all said, mistakenly, that a human cell contained forty-eight chromosomes.
Numerical modeling of the mechanics of the interaction of DNA nucleotides
Published in Mechanics of Advanced Materials and Structures, 2022
The average weight of a nucleotide (in salt solution) = 325 daltons (1 dalton equals the mass of a single hydrogen atom, or 1.66057 · 10−27 kg) [16], which is 325 × 1.6605 · 10−27 = 5.397 · 10−25 kg. The diameter of the DNA double helix is 2.0 nm. DNA has a Young’s modulus of the order of 0.3–1.0 GPa, similar to hard plastic, see [17]. The force acting between nucleotides is based here on an unzipping force AFM measurement, given by Rief et al. [18] (I use this force value, while I do not exclude the possibility that there may be other values). Rief et al. mentioned, that a 10 pN force is acting on a poly-A/T oligonucleotide duplex, while 20 pN on a poly-G/C duplex (A – adenine; G – guanine; C – cytosine, and T – thymine).
Evaluating direct and indirect effects of low-energy electrons using Geant4-DNA
Published in Radiation Effects and Defects in Solids, 2020
Eunae Choi, Kwon Su Chon, Myong Geun Yoon
The biological effect of ionizing radiation is fundamentally determined by nuclear DNA (1–3). DNA consists of two strands forming a double helix and bases bound to each other by hydrogen bonds. Ionizing radiation results in physical and chemical changes in the cell followed by biological changes causing DNA damage. Major DNA damage includes single and double strand breaks (SSB and DSB) and base damages.(4–6) Such DNA damage leads to cell death, mutation, and carcinogenesis if misrepaired or unrepaired. DSB is the most detrimental of all types of DNA damage (7,8).