Abstract
Photosynthesis sustains virtually all life on planet Earth providing the oxygen we breathe and the food we eat; it forms the basis of global food chains and meets the majority of humankind's current energy needs through fossilized photosynthetic fuels. The process of photosynthesis in plants is based on two reactions that are carried out by separate parts of the chloroplast. The light reactions occur in the chloroplast thylakoid membrane and involve the splitting of water into oxygen, protons and electrons. The protons and electrons are then transferred through the thylakoid membrane to create the energy storage molecules adenosine triphosphate (ATP) and nicotinomide–adenine dinucleotide phosphate (NADPH). The ATP and NADPH are then utilized by the enzymes of the Calvin–Benson cycle (the dark reactions), which converts CO2 into carbohydrate in the chloroplast stroma. The basic principles of solar energy capture, energy, electron and proton transfer and the biochemical basis of carbon fixation are explained and their significance is discussed.
Highlights
Photosynthesis is the ultimate source of all of humankind’s food and oxygen, whereas fossilized photosynthetic fuels provide ∼87 % of the world’s energy
The light reactions of photosynthesis involve light-driven electron and proton transfers, which occur in the thylakoid membrane, whereas the dark reactions involve the fixation of CO2 into carbohydrate, via the Calvin–Benson cycle, which occurs in the stroma (Figure 3)
The light reactions involve electron transfer from water to NADP + to form nicotinomide–adenine dinucleotide phosphate (NADPH) and these reactions are coupled to proton transfers that lead to the phosphorylation of adenosine diphosphate (ADP) into adenosine triphosphate (ATP)
Summary
Photosynthesis is the ultimate source of all of humankind’s food and oxygen, whereas fossilized photosynthetic fuels provide ∼87 % of the world’s energy. Most living organisms use the complex organic compounds derived from photosynthesis as a source of energy The breakdown of these organic compounds occurs via the process of aerobic respiration, which requires the oxygen produced by photosynthesis. Aerobic respiration is an exergonic process (negative G◦) with the energy released being used by the organism to power biosynthetic processes that allow growth and renewal, mechanical work (such as muscle contraction or flagella rotation) and facilitating changes in chemical concentrations within the cell (e.g. accumulation of nutrients and expulsion of waste). Cyanobacteria themselves are thought to c 2016 The Author(s) Have evolved from simpler photosynthetic bacteria that use either organic or inorganic compounds such a hydrogen sulfide as a source of electrons rather than water and do not produce oxygen
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