Functionalities creating specific chemical

Despite the quantitative victory of molecular orbital (MO) theory, much of our qualitative understanding of electronic structure is still couched in terms of local bonds and lone pairs, that are key conceptual elements of the valence bond (VB) picture. VB theory is essentially the quantum chemical formulation of the Lewis concept of the chemical bond [1,2]. Thus, a chemical bond involves spin-pairing of electrons which occupy valence atomic orbitals or hybrids of adjacent atoms that are bonded in the Lewis structure. In this manner, each term of a VB wave function corresponds to a specific chemical structure, and the isomorphism of the theoretical elements with the chemical elements creates an intimate relationship between the abstract theory and the nature of the... 

The chemical transactions of DNA end joining are predictably similar to other DNA repair pathways and even to replication in that all of these processes manipulate base-pairing and phospho-diester bonds to create intact duplex molecules. However, the direct repair of DSBs presents biochemical challenges nniqne to these substrates. In this section, I consider both the general and the specific chemical requirements of nonhomologons DSB repair, how they are manifest in the two main pathways of repair, and the sometimes unusual properties of key enzymes that determine their function in these pathways. 

These reactions are controlled by enzymes, protein catalysts that increase the speed of chemical reactions in the cell without themselves being changed. Each enzyme catalyzes a specific chemical reaction by acting on a specific substrate, or raw material. Each reaction is just one of a in a sequence of catalytic steps known as metabolic pathways. These sequences may be composed of up to 20 enzymes, each one creating a product that becomes the substrate—or raw material—for the subsequent enzyme. Often, an additional molecule called a coenzyme, is required for the enzyme to function. For example, some coenzymes accept an electron that is re-... 

The structural complexity of organic compounds arises from carbon s small size, intermediate EN, four valence electrons, ability to form multiple bonds, and absence of d orbitals in the valence level. These factors lead to chains, branches, and rings of C atoms joined by strong, chemically resistant bonds that point in as many as four directions from each C. The chemical diversity of organic compounds arises from carbon s ability to bond to many other elements, including O and N, which creates polar bonds and greater reactivity. These factors lead to compounds that contain functional groups, specific portions of molecules that react in characteristic ways. 

DNA self-assembly could be used in a variety of ways to solve this problem molecular components (e.g., AND, OR, and NOT gates, crossbars, routing elements) could be chemically attached to DNA tiles at specific chemical moieties, and subsequent self-assembly would proceed to place the tiles (and hence circuit elements) into the appropriate locations. Alternatively, DNA tiles with attachment moieties could self-assemble into the desired pattern, and subsequent chemical processing would create functional devices at the positions specified by the DNA tiles. None of these approaches has yet been convincingly demonstrated, but it is plausible that any of them could eventually succeed to produce two- or three-dimensional circuits with nanometer resolution and precise control of chemical structure. 

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