Photosynthesis electron movement

They are the basis of many products and processes, from batteries to photosynthesis and respiration. You know redox reactions involve an oxidation half-reaction in which electrons are lost and a reduction half-reaction in which electrons are gained. In order to use the chemistry of redox reactions, we need to know about the tendency of the ions involved in the half-reactions to gain electrons. This tendency is called the reduction potential. Tables of standard reduction potentials exist that provide quantitative information on electron movement in redox half-reactions. In this lab, you will use reduction potentials combined with gravimetric analysis to determine oxidation numbers of the involved substances. 

The thylakoid lumen is the part of the chloroplast enclosed by the thylakoid membrane (Figure 17.15). During photosynthesis, electrons are pumped into the thylakoid lumen from the stroma, forming a proton gradient. Movement of the protons out of the thylakoid lumen through the CFO-CFl complex back to the stroma provides the driving force for photophosphorylation, the process of making ATP in photosynthesis. A similar mechanism is responsible for ATP synthesis in oxidative phosphorylation. 

Origins of metal-free spectra Owing to the central importance of porphyrins and related compounds in biology, there have been many attempts over the years to derive from theory the main facts of porphyrin UV-visible spectra, i.e. the positions and multiplicities of the B and Q bands. Foremost in this search has been the American theoretical chemist, Martin Gouter-man. He developed a theory of metal-free porphyrin spectra that allows an intuitive appreciation of the light-induced electronic movements that occur inside porphyrins and related molecules. Ultimately, this begins to answer questions such as why chlorins are used as sensitisers of photosynthesis. 

The photochemical reaction of photosynthesis involves the removal of an electron from an excited state of the special chlorophyll that acts as an excitation trap. The movement of the electron from this trap chi to an acceptor begins a series of electron transfers that can ultimately lead to the reduction of NADP+. The oxidized trap chi, which has lost an electron, can accept another electron from some donor, as in the steps leading to O2 evolution. Coupled to the electron transfer reactions in chloroplasts is the formation of ATP, a process known as photophosphorylation. In this section we will consider some of the components of chloroplasts involved in accepting and donating electrons a discussion of the energetics of such processes will follow in Chapter 6 (Section 6.3). 

When investigating the electron transport processes in mitochondria and chloroplasts and bacteria, it is simplest to assume that the interaction of the chain components follows the mass action law.11-14 That would mean that the free movement of individual elements of the chain in the membrane is possible and also transfer of the charge by accidental collisions. However, transfer of electrons during both respiration and photosynthesis passes along the electron transfer chain organized into definite structural complexes. Consequently a molecule possessing an electron can donate it to a... 

Electron transfer reactions are coupled to the movement of protons across membranes. Photophosphorylation uses the energy stored in the transmembrane proton gradient to phosphorylate ADP to ATP in H -ATPases (Fig. 5.15). We see that plant photosynthesis uses an abundant source of electrons (water) and of energy (the Sun) to drive the endergonic reduction of NADP, with concomitant synthesis of ATP. Experiments show that for each molecule of NADPH formed in the chloroplast of green plants, one molecule of ATP is synthesized. 

Redox reactions are involved in combustion, rusting, photosynthesis, respiration, the movement of electrons in batteries, and more. I talk about redox reactions in some detail in Chapter 8. 

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