University of Patras

About: University of Patras is a education organization based out in Pátrai, Greece. It is known for research contribution in the topics: Population & Catalysis. The organization has 13372 authors who have published 31263 publications receiving 677159 citations. The organization is also known as: Panepistímio Patrón.

Control of DNA replication licensing in a cell cycle

Abstract: To maintain genome integrity in eukaryotes, DNA must be duplicated precisely once before cell division occurs. A process called replication licensing ensures that chromosomes are replicated only once per cell cycle. Its control has been uncovered by the discovery of the CDKs (cyclin dependent kinases) as master regulators of the cell cycle and the initiator proteins of DNA replication, such as the Origin Recognition Complex (ORC), Cdc6/18, Cdt1 and the MCM complex. At the end of mitosis, the MCM complex is loaded on to chromatin with the aid of ORC, Cdc6/18 and Cdt1, and chromatin becomes licensed for replication. CDKs, together with the Cdc7 kinase, trigger the initiation of replication, recruiting the DNA replicating enzymes on sites of replication. The activated MCM complex appears to play a key role in the DNA unwinding step, acting as a replicating helicase and moves along with the replication fork, at the same time bringing the origins to the unlicensed state. The cycling of CDK activity in the cell cycle separates the two states of replication origins, the licensed state in G1-phase and the unlicensed state for the rest of the cell cycle. Only when CDK drops at the completion of mitosis, is the restriction on licensing relieved and a new round of replication is allowed. Such a CDK-regulated licensing control is conserved from yeast to higher eukaryotes, and ensures that DNA replication takes place only once in a cycle. Xenopus laevis and mammalian cells have an additional system to control licensing. Geminin, whose degradation at the end of mitosis is essential for a new round of licensing, has been shown to bind Cdt1 and negatively regulate it, providing a new insight into the regulation of DNA replication in higher eukaryotes.

Electronic structure and nonlinear optical rectification in a quantum dot: effects of impurities and external electric field

Abstract: The electronic structure of a spherical quantum dot with parabolic confinement that contains a hydrogenic impurity and is subjected to a DC electric field is studied. In our calculations we vary the position of the impurity and the electric field strength. The calculated electronic structure is further used for determining the nonlinear optical rectification coefficient of the quantum dot structure. We show that both the position of the impurity and the strength of the electric field influence the nonlinear optical rectification process.

The importance of being red when young: anthocyanins and the protection of young leaves of Quercus coccifera from insect herbivory and excess light.

Abstract: Young leaves of many plants are transiently red because of the accumulation of anthocyanins, with the redness disappearing as leaves mature. Among the many hypothetical functions of foliar anthocyanins, two are tested in this field study: the sunscreen photoprotective function against excess visible light and the handicap signal against herbivory. We took advantage of intraspecies variation in anthocyanin concentrations of young leaves of Quercus coccifera L. to compare in vivo chlorophyll fluorescence parameters, reflectance spectra, total phenolics and the extent of herbivory of leaves of red- and green-leaved phenotypes occupying the same habitat. Photosystem II (PSII) photochemical efficiencies obtained at various photon fluence rates of red light were similar in green and red leaves. In white light, PSII efficiencies were slightly higher in red leaves than in green leaves, indicating a slight photoprotective role of anthocyanins in the field. However, compared with red phenotypes, green phenotypes suffered greater herbivore damage, as judged by the number of leaves attacked and the area lost to herbivory. In addition, there was a positive correlation between the concentrations of anthocyanins and total phenolics. We suggest that the importance of a photoprotective anthocyanic screen is low in thin, young leaves with low chlorophyll concentrations because the green light attenuated by anthocyanins is less significant for chlorophyll excitation. However, the decreased reflectance in the green spectral band and the concomitant leveling of reflectance throughout the 400-570 nm spectral range may either make red leaves less discernible to some insect herbivores or make insect herbivores more discernible to predators, or both. Moreover, excessive herbivory may be additionally discouraged by the high phenolic concentrations in red leaves.