. Biophysical science. Biophysics. 20 : 6/ Photosynthesis 373 light photons absorbed by pigments other than chlorophyll are effective in (a). Carotenoid structure CH3 CH3 H2 H2 Carotenoid Chain -CH3' H, (b). R and R' for ft-carotene Figure 8. Carotenoid structure. Different carotenoids have different R and R' groups and exist as various cis and trans isomers. The all-trans isomer is illus- trated. For /^-carotene, both R and R' have form shown in (b). Chlorophylls, when extracted, fluoresce very strongly, and each type exhibits a characteristic fluorescence spectrum. Whole gre
. Biophysical science. Biophysics. 20 : 6/ Photosynthesis 373 light photons absorbed by pigments other than chlorophyll are effective in (a). Carotenoid structure CH3 CH3 H2 H2 Carotenoid Chain -CH3' H, (b). R and R' for ft-carotene Figure 8. Carotenoid structure. Different carotenoids have different R and R' groups and exist as various cis and trans isomers. The all-trans isomer is illus- trated. For /^-carotene, both R and R' have form shown in (b). Chlorophylls, when extracted, fluoresce very strongly, and each type exhibits a characteristic fluorescence spectrum. Whole green cells also fluoresce, always exhibiting the chlorophyll a fluorescence spectrum. This is true no matter what wavelength is used to illuminate the cells. Thus, all light energy absorbed which can be used in photosynthesis is in some fashion coupled to the chlorophyll a molecules. How this occurs is uncertain; the details of the light reaction are discussed in the next section. (Chlorophyll a fluoresces much less in the bound state in the chloro- plast than it does in extracts. In this sense, it is similar to flavin groups which also lose most of their fluorescence upon binding to protein. Pyridine nucleotides, however, do not fluoresce appreciably when free but do so when bound to protein. No general interpretation for these changes in fluorescence exists.) 6. The Light Reaction Of the three parts of photosynthesis—photodissociation of water, con- version of carbon dioxide to hexose, and photosynthetic phosphorylation —the first is unique. Just how it occurs is not fully understood. Clearly,. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ackerman, Eugene, 1920-. Englewood Cliffs, N. J. , Prentice-Hall
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