Up In Arms About Essays Process Photosynthesis?
This chapter provides an overview of oxygenic photosynthesis, with primary focus on the oxygen-evolving complex (OEC) of photosystem II (PSII). The introduction includes a general discussion of photosynthesis and a brief overview of the metals involved. This is followed by an in-depth description of the metal centers within PSII, in which the structural and electronic characterizations of the OEC are reviewed in detail. The role of chloride in PSII and the proton exit pathway are discussed. Several mechanisms proposed for the O. O bond formation in the OEC are presented, along with a few detailed mechanisms for the complete catalytic cycle obtained from quantum mechanics/molecular mechanics and density functional theory calculations. Model complexes that are functional mimics of the OEC are also briefly discussed. General discussion on plastocyanin, iron-sulfur centers, [FeFe] and [NiFe] hydrogenases, and ribulose-1,5-bisphosphate carboxylase-oxygenase is included. The chapter concludes with the implications of natural photosynthesis on the development of an artificial photosynthetic framework.
KW - Oxygen-evolving complex (OEC)
The oxygen-evolving complex of PSII is a Mn4CaO5 cluster embedded in a well-defined protein environment in the thylakoid membrane.
People are usually surprised to hear that grass is a relatively recent plant innovation. and only became common in the late Cretaceous, along with flowering plants. With grass, some , and grazers have been plentiful Cenozoic herbivores. According to , carbon dioxide levels have been falling nearly continuously for the past 150-100 million years. Not only has that decline progressively cooled Earth to the point where we live in an ice age today, but is currently considered the key reason why complex life may become extinct on Earth in several hundred million years. In the Oligocene, between 32 mya and 25 mya some plants developed a during photosynthesis known as . It allowed plants to adapt to reduced atmospheric carbon dioxide levels. C4 plants became in the Miocene, and grasses are today’s most common C4 plants and . The rest of Earth’s photosynthesizers use or , which is a water-conserving process used in arid biomes.
Models of the Oxygen-Evolving Complex of …
The ecosystems may not have recovered from Olson’s Extinction of 270 mya, and at 260 mya came another mass extinction that is called the mid-Permian or extinction, or the , although a recent study found only one extinction event, in the mid-Capitanian. In the 1990s, the extinction was thought to result from falling sea levels. But the first of the two huge volcanic events coincided with the event, in . There can be several deadly outcomes of major volcanic events. As with an , massive volcanic events can block sunlight with the ash and create wintry conditions in the middle of summer. That alone can cause catastrophic conditions for life, but that is only one potential outcome of volcanism. What probably had far greater impact were the gases belched into the air. As oxygen levels crashed in the late Permian, there was also a huge carbon dioxide spike, as shown by , and the late-Permian volcanism is the near-unanimous choice as the primary reason. That would have helped create super-greenhouse conditions that perhaps came right on the heels of the volcanic winter. Not only would carbon dioxide vent from the mantle, as with all volcanism, but the late-Permian volcanism occurred beneath Ediacaran and Cambrian hydrocarbon deposits, which burned them and spewed even more carbon dioxide into the atmosphere. Not only that, great salt deposits from the Cambrian Period were also burned via the volcanism, which created hydrochloric acid clouds. Volcanoes also spew sulfur, which reacts with oxygen and water to form . The oceans around the volcanoes would have become acidic, and that fire-and-brimstone brew would have also showered the land. Not only that, but the warming initiated by the initial carbon dioxide spike could have then warmed up the oceans enough so that methane hydrates were liberated and create even more global warming. Such global warming apparently warmed the poles, which not only melted away the last ice caps and ended an ice age that had , but deciduous forests are in evidence at high latitudes. A 100-million-year Icehouse Earth period ended and a 200-million-year Greenhouse Earth period began, but the transition appears to have been chaotic, with wild swings in greenhouse gas levels and global temperatures. Warming the poles would have lessened the heat differential between the equator and poles and further diminished the lazy Panthalassic currents. The landlocked Paleo-Tethys and Tethys oceans, and perhaps even the Panthalassic Ocean, may have all become superheated and anoxic as the currents died. Huge also happened, which may have and led to ultraviolet light damage to land plants and animals. That was all on top of the oxygen crash. With the current state of research, all of the above events may have happened, in the greatest confluence of life-hostile conditions during the eon of complex life. A recent study suggests that the extinction event that ended the Permian may have lasted only 60,000 years or so. In 2001, a bolide event was proposed for the Permian extinction with great fanfare, but it does not appear to be related to the Permian extinction; the other dynamics would have been quite sufficient. The Permian extinction was the greatest catastrophe that Earth’s life experienced since the previous supercontinent existed in the .