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Biomedical subjects

M D Frank-Kamenetskiĭ

Publications and source records attributed to M D Frank-Kamenetskiĭ.

10 recordsLinked to original sources
PubMedDate not supplied

[Biophysics of the DNA molecule: a new trend].

Briefly discussed are experiments with single molecules, representing a novel trend in the biophysical study of DNA. The techniques of optical and magnetic tweezers whereby external force can be applied to individual DNA molecules were used to assess the structural transitions of the DNA double helix under such conditions. Discussed are the latest data on the dependence of the rate of complementary chain synthesis by DNA polymerase on the stretching of the template.

Biophysics↗
PubMedDate not supplied

[Fusion of complexes of DNA and extended ligands].

The theory of melting of DNA complexes with extended ligands (ties) is considered. Influence of ties interacting electorally with certain DNA regions and influence of extender ties, interacting unelectorally on the helix coil transition parameters is compared. It has been shown that both types of ties cause, coincided qualitatively, but differed quantatively, shifts of melting temperature and change of the melting range width of DNA. Comparison of theory with experiment in the case of DNA complexes with ribonuclease is given.

Chemical Phenomena↗
PubMedDate not supplied

[The ability of neuronal networks to generalize using an induction method].

Inductive generalization means the ability of a neural network to learn a given algorithm using incomplete information about it. A consideration based on the information theory leads to a simple equation connecting characteristics of the network with those of the algorithm to be learned. The main conclusion is that the most efficient generalization is achieved on the networks with minimal complexity sufficient for realization of the algorithm under consideration. The obtained equation is compared with the results of computer simulations for a universal neural network obtained in the present paper as well as by other workers. A good agreement is observed between theoretical predictions for generalization efficacy and results of computer simulations.

Generalization, Response↗
PubMedDate not supplied

[Physical models of neural networks].

The state of art in computer modelling of neural networks with associative memory is reviewed. The available experimental data are considered on learning and memory of small neural systems, on isolated synapses and on molecular level. Computer simulations demonstrate that realistic models of neural ensembles exhibit properties which can be interpreted as image recognition, categorization, learning, prototype forming, etc. A bilayer model of associative neural network is proposed. One layer corresponds to the short-term memory, the other one to the long-term memory. Patterns are stored in terms of the synaptic strength matrix. We have studied the relaxational dynamics of neurons firing and suppression within the short-term memory layer under the influence of the long-term memory layer. The interaction among the layers has found to create a number of novel stable states which are not the learning patterns. These synthetic patterns may consist of elements belonging to different non-intersecting learning patterns. Within the framework of a hypothesis of selective and definite coding of images in brain one can interpret the observed effect as the "ideaś generating" process.

Animals↗
PubMedDate not supplied

[Theory of DNA melting in the interval of B-A transition].

Theory of DNA melting within the B--A transition range is presented. The phase diagram in coordinates alcohol--temperature is plotted. The temperature shift of DNA helix--coil transition in the B--A transition point is predicted to be delta T = 3 degrees. The temperature rise of DNA melting in the range of B--A transition is caused by the presence of junctions between regions in B and A forms in helical sections.

DNA↗
PubMedDate not supplied

[Fluctuational mobility of DNA].

The avaliable data on equilibrium fluctuations in DNA are critically analyzed. Fluctuations of these types are considered: bending and torsional fluctuations and fluctuational opening of base pairs. The latest experimental and theoretical work has made it possible to estimate the bending and torsional stiffnesses of the double helix. Either of these stiffnesses has been determined by at least two different methods that have led to the same results. The stiffness of the double helix is definitely shown to be independent of the concentration of counterions when it exceeds 10(-2) M Na+. As to the fluctuational opening, the current literature is controversial and different methods lead to contradictory results. The method based on DNA unwinding by formaldehyde is considered in some detail. Strong evidence is presented in favour of the modification of base pairs without their complete opening, through an "outside" reaction. Incorporation of this modification route into the theoretical model of DNA unwinding eliminates the last descrepancies between theory and experiment. The successful accounting for all details of the process of DNA unwinding by formaldehyde is argued to prove the adequacy of the helix-coil transition theory as a basis for describing the process of base-pairs opening. The conclusion of McGhee and von Hippel, who obtained a highly overestimated value of the base-pair opening probability proceeding from the formaldehyde kinetics, is shown to be based on an erroneous assumption. The NMR data of Early et al. are briefly discussed. They strongly support the author's concept. A critical comment is made concerning the interpretation of the hydrogen exchange data by Mandel, Kallenbach and Englander. The highly overestimated value of the probability of base-pair opening claimed by these authors is most probably based on unjustified assumptions.

Base Composition↗
PubMedDate not supplied

[Effect of additional links weakening or stabilizing the double helix at the melting point of DNA].

Within the framework of the contemporary helix-coil transition theory the dependence of DNA melting temperature on the concentration of modified links stabilizing or destabilizing the double helix is calculated. The calculations show that at all values of the stabilization (destabilization) energy the shift in the melting temperature is strictly proportional to the concentration of modified links. The dependence of the slopes of these curves is calculated for the first time. The available data on the effect of chemical modification upon the DNA melting temperature are discussed in the light of the theoretically obtained results.

DNA↗