Thylakoid structure

Allen, J.F. and Forsberg, J. (2001) Molecular recognition in thylakoid structure and function. Trends Plant Sci., 6, 317-326. 

The thylakoids and stroma are the sites of the so-called light and dark reactions of photosynthesis, respectively. This compartmentalization of photosynthetic functions was recognized by Park and Pon when they broke open the chloroplasts, separated the contents into thylakoid and stroma fractions and examined their properties. The specific activities of the thylakoids include photochemical reactions, electron transport, oxygen evolution, ATP synthesis and NADP reduction, while the stroma contains enzymes for CO2 fixation driven by ATP and NADPH and other biochemical reactions in the dark. Our understanding and appreciation of the detailed structure and organization of the thylakoid membranes has increased tremendously in recent years. Further discussion of thylakoid structure will be continued in section VII on page 26. 

Allen, J. F., and Forsberg, J., Molecular Recognition in Thylakoid Structure and Function, Trends PlantSci., 6(7) 317—326,2001. 

J. Barber, Influence of Surface Charges on Thylakoid Structure and Function, Ann. Rev. Plant Physiol 33, 261-295 (1982). 

Barber, J. (1982). Influence of surface charges on thylakoid structure and function. Ann. Rev. Plant Physiol. 33 261-295 Loach, P.A., Parkes, P.S., Bustamante, P. (1984). Regulation of photosynthetic unit structure in Rhodospirillum rubrum whole cells. In Sybesma C. (ed) Adv. Photosynth. Res. vol II. 189-197 Holmes, N.G. and Allen, J.F. (1986). Protein phosphorylation as a control for excitation energy transfer in Rhodospirilium rubrum. FEBS Lett. 200 144-148... 

Barber J. (1982) Influence of surface charges on thylakoid structure and function. Ann. Rev. Plant. Physiol. 33 261-95... 

Plant cells contain a unique family of organelles, the plastids, of which the chloroplast is the prominent example. Chloroplasts have a double membrane envelope, an inner volume called the stroma, and an internal membrane system rich in thylakoid membranes, which enclose a third compartment, the thylakoid lumen. Chloroplasts are significantly larger than mitochondria. Other plastids are found in specialized structures such as fruits, flower petals, and roots and have specialized roles. 

Steponkus, P.L., Garber, M.P., Myers, S.P., Lineberger, R.D. (1977). Effects ofcold acclimation and freezing on structure and function of chloroplast thylakoids, Cryobiol. 14, 303-321. 

Anderson, J.M. (1986). Photoregulation of the composition, function, and structure of thylakoid membranes. Annual Review of Plant Physiology, 37, 93-136. 

Understanding mechanisms controlling metabolon localization in plastids of different membrane architectures Little is known about metabolon structure, assembly, and membrane targeting. The carotenoid biosynthetic pathway exists on plastid membranes. However, plastids have different membrane architectures and therefore tissue- and plastid-specific differences in membrane targeting of the biosynthetic metabolon can be expected. Localization in chloroplasts that harbor both thylakoid and envelope membranes differs from the envelope membranes in endosperm amy-loplasts. In fact, localization on both thylakoid and envelope membranes implies that the carotenoid pathway is really not a single pathway, but a duplicated pathway that may very well have membrane-specific roles with regard to functions in primary and secondary metabolism. 

The photosynthetic apparatus in green plants and algae is located in the chloroplast, which is a flattened, double-membraned structure about 150-200 A thick/4,5 The two flat membranes lie one above the other and are united at their peripheries. These double-membraned structures have been termed thylakoids (from the Greek sacklike )/ Each membrane of the thylakoid consists of a water-insoluble lipoprotein complex which contains the light-absorbing chlorophyll and other pigments utilized in photosynthesis. 

In plants, the photosynthesis reaction takes place in specialized organelles termed chloroplasts. The chloroplasts are bounded in a two-membrane envelope with an additional third internal membrane called thylakoid membrane. This thylakoid membrane is a highly folded structure, which encloses a distinct compartment called thylakoid lumen. The chlorophyll found in chloroplasts is bound to the protein in the thylakoid membrane. The major photosensitive molecules in plants are the chlorophylls chlorophyll a and chlorophyll b. They are coupled through electron transfer chains to other molecules that act as electron carriers. Structures of chlorophyll a, chlorophyll b, and pheophytin a are shown in Figure 7.9. 

The primary photochemical reaction is an electron transfer reaction which occurs within a highly structured reaction-center protein which spans the thylakoid membrane. 

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