After reaching the primary electron acceptor…
(2) QB- does accept a second electron before the next step, though, to become QB-2, which then accepts two protons from the cytoplasmic side of the membrane to form QBH2. The net effect, then, is that two electrical excitation events have been transduced to a two-electron chemical reduction event.
chemical equation for photosynthesis:
Light energy (a photon of light) is absorbed by PSII, exciting P680 and making it into a good electron donor that reduces the first member of the electron transport chain, pheophytin.
You have already studied the "dark reaction" and I will refer you to Dr. Diwan's notes on the subject. As the overall process of photosynthesis involves a series of electron transfer reactions, we are in the realm of oxidation-reduction chemistry, and it would help to review the basics of these processes because we will be going into this topic in greater depth. There is a direct analogy to electron transfer in the mitochondrion, in which clumps of energy are transferred from one electron carrier to another along a "chain" and H+ ions are translocated out, across the mitochondrial membrane, thus generating an electrochemical gradient. The energy inherent in this gradient is used to synthesize ATP in the process of "oxidative phosphorylation." The same processes occur in photosynthesis and the chloroplast, the site of photosynthesis in plants and blue-green algae (but not in photosynthetic bacteria), is the analog of the mitochondrion in eukaryotes.
Terminal electron acceptor - Biology-Online Dictionary
Oxygenic photosynthesis occurs in, among others, eukaryotic microorganisms like algae and in bacteria such as cyanobacteria; the same mechanism is at work in both. Electron flow happens through two different electron transport chains that are connected; together, these electron transport chains are called the . The stars of each chain are photosystem I (PSI) and photosystem II (PSII), each containing chlorophyll reaction centers surrounded by antenna pigments.
Cyclic Electron Transport in Photosynthesis
Because electrons don’t cycle back to reduce the original electron donor, this pathway is called If things are ideal and enough reducing power (extra electrons) is available, some of the electrons do travel back to reduce P700 and in the process add to the proton motive force that generates ATP (or ). When this happens, it’s called
The Chemical equation of photosynthesis: ..
The cool thing about microbes is how resistant they are to extenuating conditions. For example, when PSII is blocked, some oxygenic phototrophs can use cyclic photophosphorylation with PSI alone in a similar way to how anoxygenic phototrophs do it. Instead of oxidizing water, they use either H2S or H2 as the electron donor to provide the reducing power (the electrons) for CO2 fixation.
P700 is First electron donar and Last electron acceptor
Many of the steps in anoxygenic photosynthesis are the same as those for oxygenic photosynthesis (see the preceding section). For example, light excites the photosynthetic pigments, causing them to donate electrons to the electron transport chain and ATP is again generated from the proton motive force created by electron transport.
accepted equation of photosynthesis; ..
The purpose of photosynthesis is to harness light energy and use it to move electrons through an electron transport chain. Electron carriers are arranged, in order of increasing electropositivity within a membrane. Through this process, a proton motive force is created that is used to produce ATP.