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PS1.A: Structure and Properties of Matter

PS1.B: Chemical Reactions

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Statistical Techniques | Statistical Mechanics

The OEC can be thought of as a distorted chair with a Mn3-O4-Mn4-O5 back. Bonds to O5 are longer than the other bonds. What might that imply about the strength of the bonds compared to the other metal-oxygen bonds? What is the expected charge of the oxo ligands in the OEC? If the metal-O5 bond lengths are longer than the others, what might that imply about the charge on O5? Would it be consistent with a ligand other than an oxo ligand? What might it be?

Volcanoes and volcanology | Geology

Systems may evolve in unpredictable ways when the outcome depends sensitively on the starting condition and the starting condition cannot be specified precisely enough to distinguish between different possible outcomes. Core Idea PS3 Energy Interactions of objects can be explained and predicted using the concept of transfer of energy from one object or system of objects to another.

Antarctica :: Antarctic Treaty System

Kilauea; Mount Etna; Mount Yasur; Mount Nyiragongo and Nyamuragira; Piton de la Fournaise; Erta Ale

Three Synechocystis PCC 6803 strains with different levels of phycobilisome antenna-deficiency have been investigated for their impact on photosynthetic electron transport and response to environmental factors (i.e. light-quality, -quantity and composition of growth media). Oxygen yield and P700 reduction kinetic measurements showed enhanced linear electron transport rates—especially under photoautotrophic conditions—with impaired antenna-size, starting from wild type (WT) (full antenna) over ΔapcE- (phycobilisomes functionally dissociated) and Olive (lacking phycocyanin) up to the PAL mutant (lacking the whole phycobilisome). In contrast to mixotrophic conditions (up to 80% contribution), cyclic electron transport plays only a minor role (below 10%) under photoautotrophic conditions for all the strains, while linear electron transport increased up to 5.5-fold from WT to PAL mutant. The minor contribution of the cyclic electron transport was proportionally increased with the linear one in the ΔapcE and Olive mutant, but was not altered in the PAL mutant, indicating that upregulation of the linear route does not have to be correlated with downregulation of the cyclic electron transport. Antenna-deficiency involves higher linear electron transport rates by tuning the PS2/PS1 ratio from 1:5 in WT up to 1:1 in the PAL mutant. While state transitions were observed only in the WT and Olive mutant, a further ~30% increase in the PS2/PS1 ratio was achieved in all the strains by long-term adaptation to far red light (720 nm). These results are discussed in the context of using these cells for future H2 production in direct combination with the photosynthetic electron transport and suggest both Olive and PAL as potential candidates for future manipulations toward this goal. In conclusion, the highest rates can be expected if mutants deficient in phycobilisome antennas are grown under photoautotrophic conditions in combination with uncoupling of electron transport and an illumination which excites preferably PS1.

The shape outlined by O5-Ca-O1-Mn1 and Mn3-O2-Mn2-O3 is similar to what organic molecule? Describe how every two adjacent Mn are linked. Describe the coordination of Ca. Four waters (W1-W4) are coordinated to the OEC. No others were found in the region. What role may some of the waters have in the complex?

Difference between Cyclic and Noncyclic Photophosphorylation

It is a part of photosynthesis where ADP is converted to ATP to ultimately provide energy to a ..

The first structure of OEC above shows the two di-m-oxybridges that connect Mn4 to Mn1 and Mn3. This might give us clues as to the mechanism of water oxidation by the complex. To form O2, two water molecules are required as substrates. Presumably they bind as waters between adjacent Mns . What reaction intermediates may be bound to the Mn as water converts to O2? How many electrons are required for the complete oxidation?

Although cyanobacteria seem to be ideal organisms for producing molecular hydrogen with respect to biotechnology and genetic manipulation, their low PS2/PS1 ratio is one of the key problems. In contrast to higher plants and green algae with a PS2/PS1 ratio of about 1:1, the evolutionary adaptation of cyanobacteria to their environment resulted in a much lower ratio (see Fujita and Murakami ). In consequence, most of the absorbed light energy is used for cyclic electron transport, especially under mixotrophic conditions, and the yield of net electron flow (from water), i.e., the linear electron transport which potentially may be used for hydrogen production beyond PS1, is low. Fortunately, the PS2/PS1 ratio is tunable, as it is affected by many environmental (light quality, nutrient composition) and physiological parameters. Results of Fujita and Murakami () obtained with Synechocystis PCC 6714 cells indicated a higher PS2/PS1 ratio when their linear electron transport was up-regulated. In line with this, our observations with Synechocystis PCC 6803 show that a reduced or missing phycobilisome antenna, photoautotrophic growth conditions, and illumination with far red (PS1) light all result in an increased PS2 population and increased linear electron transport. The combination of these factors (see. Fig. ) probably will contribute to a potentially very high H2-production rate.

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Photosynthetic reaction centre ..

Improved extraction procedures gave oxygen evolving PS II(photosystem II) particles (BBY's). These particles are largepieces of granal membranes, probably lipid depleted (,, ,). Other treatments have been employed to isolatethe core particles from PS II. These core particles contain tworeaction chlorophyll- proteins, CP 47 and CP 43 and several nonchlorophyll binding (D1, D2), but are free fromchlorophyll + complexes. Core particles which retain manganesehave been successfully isolated with the two chlorophyll-proteins and a limited number of other polypeptides. CP 47 andCP 43 can be purified from the other components of PS II by theuse of SDS-PAGE or HPLC (high performance liquid chromatography)but they have no photochemical activity in isolation.

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