flow of electrons during photosynthesis? | Yahoo Answers
(4) Photooxidation: Transfer of an electron to an acceptor molecule. In photosynthesis, an excited chlorophyll molecule, Chl*, donates an electron, thereby becoming oxidized to the cationic free radical, Chl+.
of electron flow that occurs during photosynthesis?
(1) Fluorescence: Light (photons) emitted when an electronically excited molecule decays to a lower state of the same multiplicity. About 3-6% of the light absorbed by plants is dissipated in this way.
The reaction is energetically uphill and is driven by the transmembrane proton electrochemical gradient. The ATP synthase enzyme is a molecular rotary motor. Protons move through a channel in the ATP synthase protein (from the inner water phase to the outer water phase of the vesicle) providing the energy for ATP synthesis. However, the protons are not involved in the chemistry of adding phosphate to ADP at the catalytic site. Although it has not been proven, it appears that proton flow drives the rotation part of the ATP synthase at rates as high as one hundred revolutions per second (Figure 4). The rotation of ATP synthase can be thought of as pushing ADP and Pi together to form ATP and water.
Electron Transport in Photosynthesis
Plants have evolved a great ability to absorb light over the entire visible range of the spectra. Can they absorb to much energy? The answer is yes, so plants have developed many ways to protect themselves. IF too much light is absorbed, the pH gradient developed across the thylacoid membranes becomes greater. This is sensed by a protein, PsbS, and through subsequent conformational changes transmitted through the light-harvesting antennae, the excess light energy is dissipated as thermal energy. Mutants lacking PsbS showed decreased seed yield, a sign that it became less adaptable under conditions of stress (such as exposure to rapidly fluctuating light levels). Molecules called xanthophylls (synthesized from carotenes - vit A precursors) such as zeaxanthin are also important in excess energy dissipation. These molecules appear to cause excited state chlorophyll (a singlet like excited state dioxygen) to become deexcited. Without the xanthophylls, the excited state chlorophyll could deexcite by transfer of energy to ground state triplet dioxygen, promoting it to the singlet, reactive state, which through electron acquisition, could also be converted to superoxide. These reactive oxygen species (ROS) can lead to oxidative damage to proteins, lipids and nucleic acids, alteration in gene transcription, and even programmed cell death. Carotenoids can also acts as ROS scavengers. Hence both heat dissipation and inhibition of formation of ROS (by such molecules as vitamin E) are both mechanism of defense of excessive solar energy
Electron Transport in Photosynthesis This is an active graphic
Now what are the "Dark Phase Reactions" (aka CalvinCycle)? This is the cycle that converts CO2 into glucose. Sinceit utilizes the chemical energy in the ATP and NADPH, it does notrequire sunlight (hence the name). It is a complex cycle ofmostly phosphorylation (adding or removing phosphate) andoxidative (electron removal) chemical reactions whereby 6molecules of CO2 are converted into one molecule of glucose. Itrequires the energy-releasing cleavage of high energy bonds of 18ATPs and 12 NADPHs . The resulting 18 ADPs and 12 NADP+s are thenrestored by the Light Phase process to their high energy forms(ATP and NADPH).
(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.