Cell cycle control and cancer

This review consists of two parts. In the first part normal mechanisms regulating the progression of cells through the cell cycle are briefly reviewed. Besides mitogenic stimulation, cyclin kinase inhibition, the G1 restriction point and the prb pathway, accuracy of DNA replication and DNA repair, the G2 to M transition, apoptosis and the p 53 pathway, proteolytic, in particular ubiquitindependent mechanisms involved in the initiation of DNA synthesis in the separation of sister chromatids and in the telophase to GO/G1 transition, are discussed. In the second part oncogene and tumor suppressor gene products are briefly characterized. Aberrations of cell cycle control mechanisms associated with cancer are grouped as follows : deregulation of protooncogenes by translocations juxtaposing protooncogenes to immunoglobulin — or T cell receptor genes; translocations producing chimeric proteins unique to cancer cells; inversions and amplifications resulting in over expression of regulator genes; and deletions and mutations of tumor suppressor genes. It is emphasized that cancer is the result of a multistep process and that uncontrolled cell production and other alterations are, as a rule, late phenomen

Symmetry and structure of carbon-nitrogen complexes in gallium arsenide from infrared spectroscopy and first-principles calculations

Molecular-like carbon-nitrogen complexes in GaAs are investigated both experimentally and theoretically. Two characteristic high-frequency stretching modes at \num{1973} and \SI{2060}{cm^{-1}}, detected by Fourier transform infrared absorption (FTIR) spectroscopy, appear in carbon- and nitrogen-implanted and annealed layers. From isotopic substitution it is deduced that the chemical composition of the underlying complexes is CN$_2$ and C$_2$N, respectively. Piezospectroscopic FTIR measurements reveal that both centers have tetragonal symmetry. For density functional theory (DFT) calculations linear entities are substituted for the As anion, with the axis oriented along the \hkl direction, in accordance with the experimentally ascertained symmetry. The DFT calculations support the stability of linear N-C-N and C-C-N complexes in the GaAs host crystal in the charge states ranging from $+3$ to $-3$. The valence bonds of the complexes are analyzed using molecular-like orbitals from DFT. It turns out that internal bonds and bonds to the lattice are essentially independent of the charge state. The calculated vibrational mode frequencies are close to the experimental values and reproduce precisely the isotopic mass splitting from FTIR experiments. Finally, the formation energies show that under thermodynamic equilibrium CN$_2$ is more stable than C$_2$N

[μ-3,3′-Bis(tri­hydro­bor­yl)[3]ferroceno­phane]bis­(chlorido­zirconocene)

The title compound, [FeZr2(C5H5)4Cl2(C13H18B2)], is a heteronuclear complex that consists of a [3]ferrocenophane moiety substituted at each cyclo­penta­dienyl (Cp) ring by a BH3 group; the BH3 group is bonded via two H atoms to the Zr atom of the zirconocene chloride moiety in a bidentate fashion. The two Cp rings of the [3]ferrocenophane moiety are aligned at a dihedral angle of 8.9 (4)° arising from the strain of the propane-1,3-diyl bridge linking the two Cp rings. [One methyl­ene group is disordered over two positions with a site-occupation factor of 0.552 (18) for the major occupied site.] The dihedral angles between the Cp rings at the two Zr atoms are 50.0 (3) and 51.7 (3)°. The bonding Zr(...)H distances are in the range 1.89 (7)–2.14 (7) Å. As the two Cp rings of the ferrocene unit are connected by an ansa bridge, the two Zr atoms approach each other at 6.485 (1) Å. The crystal packing features C—H(...)Cl inter­actions

Zur Verbreitung von Cyperus fuscus L. in Westniedersachsen

Cyperus fuscus L., das braune Cypergras, ist eine einjährige Nanocyperion-Art, die in den vergangenen 40 Jahren in Westniedersachsen sehr selten geworden ist. Ihre aktuelle Verbreitung in diesem Gebiet und ein neuer Standort werden dargestellt

Ergänzungen zur Flora von Südwest-Niedersachsen und dem benachbarten Westfalen : Taraxacum lacistophyllum (Dahlst.) Raunk. und Taraxacum subundulatum Dahlst. ; Herrn Prof. Dr. Dr. H. E. Weber in großer Dankbarkeit zum 65. Geburtstag gewidmet

Zwei in Südwestniedersachsen erstmals beobachtete Taraxacum-Arten, T. lacistophyllum und T. subundulatum, werden vorgestellt.For the first time, two species of the genus Taraxacum, T. lacistophyllum and T. subundulatum have been found in the southwest of Lower Saxony. They are shown in a short presentation

Erste Übersicht über die Armleuchteralgen (Characeae) des Raumes Osnabrück

Aus Anlaß des Wiederfundes von Chara contraria A. Sr., die zületzt 1897 in Niedersachsen festgestellt worden war, werden die derzeit bekannten Arten der Armleuchteralgen (Characeae) und ihre Verbreitung im Raum Osnabrück vorgestellt. Ein Sestimmungsschlüssel ist beigegeben.On the occasion of the rediscovery of Chara contraria A. Sr., which was found for the last time in 1897 in Lower Saxony, the known species of the Characeae and their distribution in the area of Osnabrück (Lower Saxony, Germany) is shown. A key to the species is enclosed

The dehydration of alcohols in the presence of chloroform and alkali

M.S.Jack Hin