THEORETICAL DISTRIBUTION OF TWO-DIMENSIONAL PROJECTIONS IN ELECTRON-MICROSCOPIC SECTIONS
| Autor: | N. B. Grover, George H. Weiss |
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| Rok vydání: | 1968 |
| Předmět: | |
| Zdroj: | Proceedings of the National Academy of Sciences. 60:80-85 |
| ISSN: | 1091-6490 0027-8424 |
| DOI: | 10.1073/pnas.60.1.80 |
| Popis: | In a previous article' some of the features of ribosome strands were discussed. In the present paper we shall present the methodology and results of a study of the distribution of ribosome strand lengths. It is not clear a priori whether the strands observed in the electron-microscopic sections are slices of a single, long, and convoluted strand, whether they are samples from an inherent distribution of strand lengths, or whether they are slices of strands originally of uniform length. We may shed some light on this problem by examining statistics of the observed distribution of strand lengths and by testing the hypothesis that this distribution is consistent with the strands having a single standard length. Although the strands may be of the same length in vivo, a variation of lengths will always be observed, due in part to the different inclinations of the strands with respect to the plane of sectioning, and in part to the fact that a section may contain only a terminal part of a strand, the rest having been cut off in the sectioning process. Recently,2 the same problem has been treated from a different point of view by Perl, who tried to find the distribution of the number of ribosomes in a strand from the numbers appearing in electron-microscopic sections. Both methods of inferring underlying distributions are necessarily approximate. In our approach, since the ribosomes are electron-opaque and the core column of the strands is electron-transparent, we are able to include in the measurement only that part of each strand outlined by ribosomes. Thus, if any core strand extended from a terminal ribosome to the plane of transection, this would introduce an error into the determination of the actual length of the transected strand. In addition, we have neglected any curvature effects that may occur perpendicular to the plane of sectioning. Perl, on the other hand, has adopted an arbitrary convention regarding when to count one ribosome as two in those cases where one of the ribosomes may be partially hidden by the other. Hence the two approaches can be regarded as complementary. In this paper we present theoretical histograms for the observed length distribution when the strands are of constant length. The various parameters used in our models are shown in Figure 1. Three assumptions will be made: (1) That the section has a constant thickness t. |
| Databáze: | OpenAIRE |
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