Details of Photosynthesis Coming to Light

first_img1Amuntz, Drory and Nelson, “The structure of a plant photosystem I supercomplex at 3.4-angstrom resolution,” Nature 447, 58-63 (3 May 2007) | doi:10.1038/nature05687.2Skourtis and Beratan, “Photosynthesis from the Protein’s Perspective,” Science, 4 May 2007: Vol. 316. no. 5825, pp. 703-704, doi: 10.1126/science.1142330.3The second paper also spoke of the efficient use of quantum mechanical properties of light: “The experimental data reported by Wang et al. also encourage renewed theoretical attention to the early events in photosynthesis.  Models that include quantized nuclear dynamics seem particularly important, because high-frequency quantum modes influence fast electron transfer, producing nonexponential kinetics and unusual temperature dependence.”4“Wang et al. suggest that the slow protein dynamics discussed above may help to overcome reaction barriers produced by membrane potentials or by environmental factors that perturb the photosynthetic reaction center and potentially slow down the electron-transfer rate.  Thus, protein motion could overcome reaction barriers produced by cellular factors that might otherwise perturb the electron-transfer kinetics.”Those who studied high school biology decades ago can revel in these facts about photosynthesis that are now coming to light (pardon the pun).  At the time, our teachers and professors saw light going in, and sugars coming out, but were nearly clueless about what magic was going on inside.  The black box is now opening, and we’re finding out that highly efficient molecular machines were there all along.  So that’s how it’s done!(Visited 14 times, 1 visits today)FacebookTwitterPinterestSave分享0 New tools of science are unveiling the secrets of what was long a “black box” in biology: photosynthesis.  A paper in Nature last week1 described the structure of the plant PhotoSystem I complex (PSI) in near-atomic resolution.  Next day, a paper in Science2 described some of the protein interactions that occur when plants turn light into energy for work.  Both papers praised the exceptional efficiency of “the most efficient nano-photochemical machine in nature.”    As is common in the scientific literature, the paper in Nature used engineering language when discussing photosynthesis.  It referred to the “reaction centre” as a “light-harvesting complex” and to certain parts as “antennas.”  The authors used the root efficient eight times in the paper: for example, “This highly efficient nano-photoelectric machine is expected to interact with other proteins in a regulated and efficient manner” – there are two instances in the same sentence.  The paper ended:The complexity of PSI belies its efficiency: almost every photon absorbed by the PSI complex is used to drive electron transport.  It is remarkable that PSI exhibits a quantum yield of nearly 1 (refs 47, 48), and every captured photon is eventually trapped and results in electron translocation.  The structural information on the proteins, the cofactors and their interactions that is described in this work provides a step towards understanding how the unprecedented high quantum-yield of PSI in light capturing and electron transfer is achieved.The authors only referred to evolution once: “The two principal subunits of the reaction centre, PsaA and PsaB, share similarities in their amino acid sequences and constitute a pseudosymmetric structure that evolved from an ancient homodimeric assembly.”  Yet this was stated dogmatically without any explanation of how that could have occurred.    The paper in Science explored photosynthesis from the protein’s perspective.  The authors of this paper also spoke of the “efficient transfer of electrons across biomembranes” and the “high efficiency of the reaction (an electron is transferred for each photon absorbed)” – i.e., there is no loss or waste of input.    The authors discussed how certain protein parts physically move in response to their inputs.  These movements among the chlorophylls and other parts modulate the speed of the downstream reactions.  Rather than quote their jargon about biomechanics and biomolecular dynamics, let’s attempt an analogy that suggested itself from one of the illustrations: it’s like catching eggs dropping out of the sky into a soft, gentle net, where they can be safely transported to the kitchen.  Those who prefer the original jargon can see the footnote.4last_img read more

Four labourer buried alive while repairing tunnel in Rajasthan

first_imgFour labourers, repairing a tunnel in Rajasthan’s Sirohi district, died after being buried alive under debris, the police said on Saturday.The victims were trapped under the debris on Friday which fell due to vibrations generated by a poclain machine at the site on Beawar-Pindwara national highway, they said.The family members of the deceased, identified as Devi Singh, 32, Uttam Kumar, 23, Mahendra Kumar Meena, 27, and Mahendra Hiragar, 30, have refused to accept the bodies till they are provided compensation by the private firm which was carrying out the repair work, Sirohi collector Babu Lal Meena said.The bodies have been kept at a mortuary. The State government has announced ex-gratia for the kin of the deceased. A case has been registered against the company and the driver of the poclain machine, the police said.last_img read more

‘Nexus between Haryana officials and illegal stone crushing units exposed’

first_imgAfter the National Green Tribunal ordered an immediate closure of all illegally operating polluting stone crushers in Mahendergarh district of Haryana, political party Swaraj India on Saturday hit out at the BJP government, saying the nexus between officials and those involved in running the crushers had been exposed. “This order of the NGT exposes the collusion between the owners of the illegal crushers and the government machinery,” said party president Yogendra Yadav. “We should hope that now the State government and the local administration will respect the order and spirit of the NGT, take strict action against erring officials and others.”The NGT had on July 24 also directed the Deputy Commissioner of Mahendergarh to ensure immediate initiation of action by way of prosecution and recovery of compensation which must be deterrent and relatable to the cost of restoration so that the illegal activity was not profitable. The orders came on the petition of Mahender Singh and Tejpal Yadav, who made a submission that the location of the crushers was close to the plantation, reserved forest and an educational institution. Besides, the area is over exploited in terms of the ground water resulting in scarcity of water even for drinking purposes.The NGT, which had sought factual and action taken report from a joint committee comprising representatives of the Deputy Commissioner Mahendergarh, district Town and Country Planning, Haryana Pollution Control Board and the Divisional Forest Officer, pointed out in its order that two reports earlier submitted were found without application of mind and were rejected. The third report had been submitted which was also inadequate to deal with the matter.The NGT observed, “The report shows the State administration in poor light. There is no explanation how potable water has been continued to be drawn without any restriction by the State administration though the area is critical in terms of ground water and in spite of such illegality brought to notice. It is also not clear how blatant violation of air quality norms is being allowed for permitting operation of the units at the cost of public health and environment. The report does not clarify how many stone crushers, if any, are legitimate which do not conflict with the environment. It appears that the State administration has not cared to fully verify the compliance of environment norms while permitting continuation of the stone crushers, even after proceedings before this Tribunal.”The order also added that the Haryana Chief Secretary may look into the conduct of the officers, who gave the earlier reports, in withholding the information which had now been given.last_img read more