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Abstract (ger): Die Flüssigkeitsschichten, die um ein sich bewegendes Molekül herumfließen, haben infolge der endlichen Abmessungen der Flüssigkeitsmolekeln eine endliche Dicke. Die Berücksichtigung dieses Umstandes führt zu einer Modifikation der Stokesschen Gesetze der Kontinuumstheorie für den Zusammenhang zwischen Reibung und Viskosität. Es ergibt sich die richtige Größenordnung und ungefähr die richtige Radienabhängigkeit der beobachteten Mikroreibung, und zwar sowohl für die Rotation als auch für die Translation.
Upon separation of the protein from the nucleic acid component of tobacco mosaic virus by phenol, using a fast and gentle procedure, the nucleic acid is infective in assays on tobacco leaves. A series of qualitative and quantitative control experiments demonstrates that the biological activity cannot depend on residual proteins in the preparation, but is a property of isolated nucleic acid which is thus the genetic material of the virus.
Within the sedimentation diagram of infective RNA preparations isolated from Tobacco Mosaic Virus, undegraded molecules form a sharp peak with a molecular weight corresponding to the total RNA content of the virus particle. Degradation kinetics by ribonuclease is of the linear, single-target type, indicating that the RNA is single-stranded. The intact RNA of a virus particle thus forms one big single-stranded molecule. Quantitative evaluation of the effect degradation by RNA-ase on the infectivity of the RNA shows that the integrity of the entire molecule is required for its biological activity.
The generation of viral mutants in vitro was demonstrated by treatment of the isolated RNA of Tobacco Mosaic Virus by nitrous acid. This agent causes deaminations converting cytosine into uracil, and adenine into hypoxanthine. Our assay for mutagenesis was the production of local lesions on a tobacco variety on which the untreated strain produces systemic infections only. A variety of different mutants are generated in this way. Quantitative analysis of the kinetics of mutagenesis leads to the conclusion that alteration of a single out of the 6000 nucleotides of the viral RNA is sufficient for causing a mutation.
Applying mild methods of preparation, part of the ribosomes of rabbit reticulocytes are found in aggregates (later called polyribosomes) of up to six ribosomal units. Upon treatment with RNA-ase, they desintegrate into single ribosomes. The fast-sedimenting aggregates are found to be more active in protein synthesis in terms of incorporation of radioactive amino acids, whereas the single ribosomes are more receptive to stimulation by the artificial messenger RNA poly-U. The findings indicate that the linkage of ribosomes into aggregates is due to the messenger RNA. They support a tape-reading mechanism of protein synthesis whereby growth of the peptide chain is accompanied by shifting the active site of the ribosome from one coding group of nucleotides of the messenger RNA to the next.
The short paper introduces the concept of possible branches of double-stranded DNA (later sometimes called palindromes): Certain sequences of nucleotides may be followed, after a short unpaired stretch, by a complementary sequence in reversed order, such that each DNA strand can fold back on itself, and the DNA assumes a cruciform or tree-like structure. This is postulated to interact with regulatory proteins.
Die volle Anwendbarkeit der Physik auf die Biologie des menschlichen Gehirns bedeutet nicht notwendig, dass es ein finitistisches und zugleich vollständiges, algorithmisches Verfahren der Korrelation mentaler mit physikalischen Zuständen geben kann. Vielmehr gibt es Gründe für die Hypothese, dass eine umfassende Theorie der psychophysischen Beziehung prinzipiell unmöglich sein könnte. Diese Auffassung verbindet die Universalität der Physik mit der logischen Begrenztheit des menschlichen Denkens (z. B. in Bezug auf sich selbst) und betrachtet Bewusstsein - die ursprünglichste menschliche Erfahrung - nicht als Randphänomen. ++++ Die Zeitschrift RATIO erschien bis 1987 in einer deutschen und in einer englischen Ausgabe. Die englische Version des Artikels lautet: A. Gierer, The physical foundations of biology and the problems of psychophysics. RATIO XII, No. 1, 1970. S. 47-64.
Full applicability of physics to human biology does not necessarily imply that one can uncover a comprehensive, algorithmic correlation between physical brain states and corresponding mental states. The argument takes into account that information processing is finite in principle in a finite world. Presumbly the brain-mind-relation cannot be resolved in all essential aspects, particularly when high degrees of abstraction or self-analytical processes are involved. Our conjecture plausibly unifies the universal validity of physics and a logical limitation of human thought, and it does not regard consciousness -the most basic human experience - as a marginal phenomenon. ++++ RATIO appeared up to 1987 in both a German and an English version. The German title of this article: Alfred Gierer, Der physikalische Grundlegungsversuch in der Biologie und das psychophysische Problem. RATIO XII, Heft 1, 1970, S. 40-54.
Aggregates of previously isolated cells of Hydra are capable, under suitable solvant conditions, of regeneration forming complete animals. In a first stage, ecto- and endodermal cells sort out, producing the bilayered hollow structure characteristic of Hydra tissue; thereafter, heads are formed (even if the original cell preparation contained no head cells), eventually leading to the separation of normal animals with head, body column and foot. Hydra appears to be the highest type of organism that allows for regeneration of the entire structure from random cell aggregates. The system is particularly useful for studying cell interactions, tissue polarity, pattern formation, and cell differentiation.
