Photosynthesis and the Formation of Carbohydrates

In Chapter 1, it was stated that carbohydrates are produced on the Earth during the process of photosynthesis. A very simple reaction was written (reaction 1.1) in which 6 CO2 combined with 6 H2O to give carbohydrate, C Hj20, and six molecules of molecular oxygen, O2. It was further indicated that the energy necessary to form the carbon-carbon bonds in the synthesis of carbohydrate came from the sun. While all of this is true, the process is far more complex than the simple reaction given in Chapter 1. 

Essentials of Carbohydrate Chemistry Springer-Verlag New York Inc. 1998 

Photosystem I. contains chlorophyll a and other pigments that trap photons, exciting electrons. The excited electrons leave the system and reduce ferredoxin. The system is returned to the ground state by electrons from the electron transport chain. 

The positively charged, excited chlorophyll in Photosystem I is brought back to its ground state by picking up two electrons from an electron transport system. The electron transport system is a series of redox enzymes that pass high-energy 

But nature has chosen the unlikely candidate, water, as the primary reducing agent for most photosynthesizing systems, probably because of its abundance when the process of photosynthesis was evolving. 

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Photosynthesis is the reverse of reaction (30.1) the formation of carbohydrates and oxygen from water and carbon dioxide with solar energy. Photosynthesis occurs in the chloroplasts contained in the cells of green plants. The chloroplasts hold two types of photosynthetic systems, which are called PSl and PS 11. These systems... 

Photosynthesis. The formation of carbohydrates in green plants by the process of photosynthesis is described in ihc entry on Photosynthesis. The synthetic mechanism involves the addition of carbon dioxide to ribulose-1,5-diphosphate and the subsequent formation of two molecules of 3-phosphoglyccric acid which are reduced to glyceraldehyde-3-phosphate. The triose phosphates are utilized to again from ribulose-5-phosphates by enzymes of the pentose phosphate cycle Phosphorylation or ribulose-5-phosphate with ATP regenerates ribulose-1.5-diphosphate to accept another molecule of carbon dioxide. See also Phosphorylation (Photosynthetlc). 

Carbohydrates are formed in green plants by photosynthesis, which is the chemical combination, or fixation, of carbon dioxide and water by utilization of energy from the absorption of visible light. The overall result is the reduction of carbon dioxide to carbohydrate and the formation of oxygen ... 

The end result of the photochemical part of photosynthesis is the formation of 02, NADPH, and ATP. Much of the oxygen is released to the atmosphere, but the NADPH and ATP are utilized in a series of dark reactions that achieve the reduction of carbon dioxide to the level of a carbohydrate (fructose). A balanced equation is... 

From the point of view of organic synthesis, the overall process consists of the formation of carbohydrates (CH20) by the reduction of carbon dioxide. The essence of the process is the use of photochemical energy to split water and concomitantly to reduce C02. Many proteins and small molecules are involved in photosynthetic machinery. Inorganic species are in the centre of photosynthesis as pigments in light harvesting, substrates, products, catalysts, and electron transfer mediators. 

Biosynthesis of carbohydrates from carbon dioxide occurs in the stroma region of the chloroplasts via the Calvin cycle. The formation of a six-carbon sugar molecule requires six complete turns of the Calvin cycle, for each of which three ATP and two NADPH molecules are consumed. The overall biochemistry of photosynthesis for the formation of one glucose molecule from six CO2 molecules may be written as ... 

Apart from fossil raw materials, atmospheric carbon dioxide provides a further source of chemical carbon, via photosynthesis, i.e. the formation of carbohydrates from carbon dioxide and water using energy from the sun. Photosynthesis produces around 2x10" t of biomass annually, with an energy content of 3x10 Joule. 

Although seen only occasional during the first half of this century, winter injury of first-year red spruce needles has become an annual event in the coniferous montane forest area, resulting in the formation of red-brown first year needles that subsequently desiccate and are shed 20, 21). The loss of foliage reduces photosynthesis and the obligatory accumulation of carbohydrate in the twigs and root systems. There is some evidence that this phenomenon involves both natural and anthropogenic causal factors. 

The basis of photosynthesis - consecutive chain of redox reactions, during which electrons are transferred from donor-reducer to acceptor-oxidizer with the formation of reduced compounds (carbohydrates) and oxygen isolation. 

Role of H2S in Some Photosynthetic Bacteria Illuminated purple sulfur bacteria carry out photosynthesis in the presence of H20 and 14C02, but only if H2S is added and 02 is absent. During the course of photosynthesis, measured by formation of [14C]carbohydrate, H2S is converted to elemental sulfur, but no 02 is evolved. What is the role of the conversion of H2S to sulfur Why is no 02 evolved ... 

In plants, stored carbohydrates, mostly in the form of starch, are hydrolyzed to glucose. Glycolysis then produces pyruvate, which is transported into mitochondria, as in animal cells. Mitochondrial oxidation of pyruvate and concomitant formation of ATP occur in photosynthetic cells during dark periods when photosynthesis is not possible, and in roots and other nonphotosynthetlc tissues all the time. I... 

The photosynthetic process in plants can be divided into four stages, each localized to a defined area of the chloro-plast (1) absorption of light, (2) electron transport leading to formation of O2 from H2O, reduction of NADP to NADPH, and generation of a proton-motive force, (3) synthesis of ATP, and (4) conversion of CO2 into carbohydrates, commonly referred to as carbon fixation. All four stages of photosynthesis are tightly coupled and controlled so as to produce the amount of carbohydrate required by the plant. All the reactions in stages 1-3 are catalyzed by proteins in the thylakoid membrane. The enzymes that incorporate CO2 into chemical intermediates and then convert them to starch are soluble constituents of the chloroplast stroma. The enzymes that form sucrose from three-carbon intermediates are in the cytosol. 

Glucose is synthesized naturally in plants and some single-celled organisms through the process known as photosynthesis. In this process, sunlight catalyzes the reaction between carhon dioxide and water that results in the formation of a simple carbohydrate (glucose) and oxygen. The overall reaction can be summarized by a rather simple chemical equation ... 

The overall statements for the energy conversions of biology have been known for more than a century. TTiey are embodied in the expressions for photosynthesis and respiration, as currently written and balanced for the formation and utilization of a carbohydrate such as glucose with six carbon (C) atoms and the equivalent of a molecule of water, H2O, for each carbon atom, consequently, the name carbohydrate. 

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