The Role of ATP in the Reaction of Photosynthesis
Photosynthesis uses light, water and carbon dioxide to create sugar. This process is divided into two stages, the light-dependent process (light reactions) and the light-independent process (dark reactions). The light reactions store light energy into ATP, or adenosine triphosphate, which is then consumed in the dark reactions to create sugar molecules.
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Structure of ATP
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ATP consists of an adenosine nucleotide attached to a ribose sugar, which is then attached to a series of three phosphate groups.
Energy in ATP
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Energy is stored in the phosphate bonds of ATP. Removing the phosphate group from ATP releases energy and produces ADP, or adenosine diphosphate, and a free phosphate group. Conversely, to add a phosphate group to ADP requires the input of energy.
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Generation of ATP in the Light Reactions
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In the light reactions, a process called photophosphorylation uses light energy to attach a phosphate to ADP, creating ATP thorough the use of a series of reactions. A second energy molecule known as NADPH is also created in the light reactions.
Photophosphorylation
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Photophosphorylation removes an electron from water, releasing oxygen in the process, which is carried down a series of redox reactions, creating a proton gradient across the thykaloid membrane by pumping protons into the thykaloid space. This proton gradient allows the enzyme ATP synthase to create ATP as protons return across the membrane.
Consumption of ATP in Dark Reactions
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In the light-independent reactions of photosynthesis, the ATP and NADPH generated during photophosphorylation are utilized to create sugar molecules.
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