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It is necessary either to supply an activation energy or to lower the intrinsic activation energy of the system, in order to make most biochemical reactions proceed at a useful rate. Living systems use complex macromolecular structures to lower the activation energies of biochemical reactions.
Under kinetic conditions, such as an enzymatic reaction with RuBisCO, the lighter isotope is favored because of a lower activation energy. Oxygenic photosynthesis is a metabolic pathway facilitated by autotrophs, including plants, algae, and cyanobacteria. This pathway converts inorganic carbon dioxide from the atmosphere or aquatic environment ...
The energized electrons transferred to plastoquinone are ultimately used to reduce NADP + to NADPH or are used in non-cyclic electron flow. [1] DCMU is a chemical often used in laboratory settings to inhibit photosynthesis. When present, DCMU inhibits electron flow from photosystem II to plastoquinone.
Enzymes can accelerate reactions in several ways, all of which lower the activation energy (ΔG ‡, Gibbs free energy) [46] By stabilizing the transition state: Creating an environment with a charge distribution complementary to that of the transition state to lower its energy [47] By providing an alternative reaction pathway:
The electron in the higher energy level is unstable and will quickly return to its normal lower energy level. To do this, it must release the absorbed energy. This can happen in various ways. The extra energy can be converted into molecular motion and lost as heat, or re-emitted by the electron as light (fluorescence).
Photorespiration involves a complex network of enzyme reactions that exchange metabolites between chloroplasts, leaf peroxisomes and mitochondria. The oxygenation reaction of RuBisCO is a wasteful process because 3-phosphoglycerate is created at a lower rate and higher metabolic cost compared with RuBP carboxylase activity.
The following is a breakdown of the energetics of the photosynthesis process from Photosynthesis by Hall and Rao: [6]. Starting with the solar spectrum falling on a leaf, 47% lost due to photons outside the 400–700 nm active range (chlorophyll uses photons between 400 and 700 nm, extracting the energy of one 700 nm photon from each one)
Since bulk molecules can be excluded from the active site this energy output can be minimised. Next, the active site is designed to reorient the substrate to reduce the activation energy for the reaction to occur. The alignment of the substrate, after binding, is locked in a high energy state and can proceed to the next step.