Chloroplasts volume

The Boyle-Van t Hoff relation applies to the equilibrium situation for which the water potential is the same on either side of the two membranes surrounding a chloroplast. When T1 equals T°, net water movement across the membranes ceases, and the volume of a chloroplast is constant. (The superscript i refers to the inside of the cell or organelle and the superscript o to the outside.) If we were to measure the chloroplast volume under such conditions, the external solution would generally be at atmospheric pressure (P° =0). By Equation 2.13a (T = P — H, when the gravitational term is ignored), the water potential in the external solution is then... 

Figure 2-11. Volumes of pea chloroplasts at various external osmotic pressures, 11°. The chloroplasts were isolated from plants in the light or the dark, indicating that illumination decreases chloroplast volume. [Source Nobel (1969b) used by permission.]...

To illustrate the use of Equation 2.18 in interpreting osmotic data, we will consider osmotic responses of pea chloroplasts suspended in external solutions of various osmotic pressures. It is customary to plot the volume V versus the reciprocal of the external osmotic pressure, l/n°, so certain algebraic manipulations are needed to express Equation 2.18 in a more convenient form. After transferring r1 — P1 to the left-hand side of Equation 2.18 and then multiplying both sides by VwrCwf II0 — r1 + / ), can be shown to equal RT -n -/(Jl° — r1 +/>1). The measured chloroplast volume V can be... 

The relatively simple measurement of the volumes of pea chloroplasts for various external osmotic pressures can yield a considerable amount of information about the organelles. If we measure the volume of the isolated chloroplasts at the same osmotic pressure as in the cytosol, we can determine the chloroplast volume that occurs in the plant cell. Cell sap expressed from young pea leaves can have an osmotic pressure of 0.70 MPa such sap comes mainly from the central vacuole, but because we expect n05 10801 to be essentially equal to nvacuole (Eq. 2.14), nce11 8ap is about the same as n05 10801 (some uncertainty exists because during extraction the cell sap can come into contact with water in the cell walls). At an external osmotic pressure of 0.70 MPa (indicated by an arrow and dashed vertical line in Fig. 2-11), pea chloroplasts have a volume of 29 pm3 when isolated from illuminated plants and 35 pm3 when isolated from plants in the dark (Fig. 2-11). Because these volumes occur at approximately the same osmotic pressure as found in the cell, they are presumably reliable estimates of pea chloroplast volumes in vivo. 

The intercept on the ordinate in Figure 2-11 is the chloroplast volume theoretically attained in an external solution of infinite osmotic pressure —a l/n° of zero is the same as a n° of infinity. For such an infinite 11°, all of the internal water would be removed = 0), and the volume, which is obtained by extrapolation, is that of the nonaqueous components of the chloroplasts. (Some water is tightly bound to proteins and other substances and presumably remains bound even at the hypothetical infinite osmotic pressure such water is not part of the internal water, Vwn v). Thus the intercept on the ordinate of a F-versus-l/n° plot corresponds to b in the conventional Boyle-Van t Hoff relation (Eq. 2.15). This intercept (indicated by an arrow in Fig. 2-11) equals 17 pm3 for chloroplasts both in the light and in the... 

C. Suppose that chloroplasts are isolated in 0.3 m sucrose, which has a reflection coefficient of 1.00 for the chloroplasts. If 0.1 mol of glycine is then added per kilogram of water in the isolation medium, and if the chloroplast volume is 23 j.im3, what is the reflection coefficient of glycine for the chloroplast membranes ... 

D. What is the external concentration of glycerol (ay = 0.60) in which the chloroplasts have the same initial volume as in 0.3 m sucrose What is the chloroplast volume after a long time in the glycerol solution ... 

C. The chloroplast volume did not change with the addition of glycine to the external solution hence o-giycjne is zero (see Eq. 3.43). 

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. 

A decade after the discovery of the Rieske protein in mitochondria (90), a similar FeS protein was identified in spinach chloroplasts (91) on the basis of its unique EPR spectrum and its unusually high reduction potential. In 1981, the Rieske protein was shown to be present in purified cytochrome Sg/complex from spinach (92) and cyanobacteria (93). In addition to the discovery in oxygenic photosynthesis, Rieske centers have been detected in both single-RC photosynthetic systems [2] (e.g., R. sphaeroides (94), Chloroflexus (95)) and [1] (Chlo-robium limicola (96, 97), H. chlorum (98)). They form the subject of a review in this volume. 

Volume 97. Biomembranes [Part K Membrane Biogenesis Assembly and Targeting (Prokaryotes, Mitochondria, and Chloroplasts)]... 

Volume 125. Biomembranes (Part M Transport in Bacteria, Mitochondria, and Chloroplasts General Approaches and Transport Systems)... 

Kumar, S. and Daniell, H. (2004). Engineering the chloroplast genome for hyperexpression of human therapeutic antigens. InRecombinant Gene Expression. Methods Molecular Biology, volume 267. New York Springer. 

Topical eukaryotic cells (Fig. 1-7) are much larger than prokaryotic cells—commonly 5 to 100 pm in diameter, with cell volumes a thousand to a million times larger than those of bacteria. The distinguishing characteristics of eukaryotes are the nucleus and a variety of membrane-bounded organelles with specific functions mitochondria, endoplasmic reticulum, Golgi complexes, and lysosomes. Plant cells also contain vacuoles and chloroplasts (Fig. 1-7). Also present in the cytoplasm of many cells are granules or droplets containing stored nutrients such as starch and fat. 

Like Complex III of mitochondria, cytochrome b6f conveys electrons from a reduced quinone—a mobile, lipid-soluble carrier of two electrons (Q in mitochondria, PQb in chloroplasts)—to a water-soluble protein that carries one electron (cytochrome c in mitochondria, plastocyanin in chloroplasts). As in mitochondria, the function of this complex involves a Q cycle (Fig. 19-12) in which electrons pass, one at a time, from PQBH2 to cytochrome bs. This cycle results in the pumping of protons across the membrane in chloroplasts, the direction of proton movement is from the stromal compartment to the thylakoid lumen, up to four protons moving for each pair of electrons. The result is production of a proton gradient across the thylakoid membrane as electrons pass from PSII to PSI. Because the volume of the flattened thylakoid lumen is small, the influx of a small number of protons has a relatively large effect on lumenal pH. The measured difference in pH between the stroma (pH 8) and the thylakoid lumen (pH 5) represents a 1,000-fold difference in proton concentration—a powerful driving force for ATP synthesis. 

The volume given by Eq. 9-33 is about 1.4 x 10-11 cm3, which could be represented approximately by a cube 2.4 pm on a side. If we compare this volume with that of a cell (Table 1-2) or of an organelle, we see that in one second an enzyme molecule will sweep out a large fraction of the volume of a small cell, mitochondrion, chloroplast, etc. 

Volume of chloroplast per unit volume of single cell Period until next branching of GP in Eq. (4)... 

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