Nanometer helix

Described in 1953 by James Watson and Francis Crick, the double helix of DNA (deoxyribonucleic acid) is the cellular storehouse of genetic information. This biopolymer consists of a pair of complementary chains approximately 2.4 nanometers (9.5XlO-8 inches) in diameter and composed of... 

Melting and helix formation of nucleic acids are often detected by the absorbance of ultraviolet light. This process can be understood in the following way The stacked bases shield each other from light. As a result, the absorbance of UV light whose wavelength is 260 nanometers (the Amo) of a double-helical DNA is less than that of the same DNA, whose strands are separated (the random coil). This effect is called the hypochromicity (less-color) of the double-helical DNA. 

The move was protracted, as so often in history. The incentive came from the discovery of the DNA double-helix by Watson and Crick, and from the ensuing lecture by Richard P. Feynman in 1959, calling for the devising of small mechanical engines and devices operating at the nanometer scale. 

The atomic force microscope (AFM) is a very high resolution imaging device with a resolution of less than a nanometer, and has been used to probe the surface of many samples including living cells. Many reports during this review period have used AFM, and only selected publications are included here. AFM has been used to visualise G-quadruplexes from telomeric DNA, a DNA six-helix bundle and mRNA. Some protein-nucleic add structures that have been examined by AFM include E.coli RNA polymerase, EcoKI restriction enzyme, the E.coli ami-nopeptidase A (PepA) and nucleoprotein complexes. ... 

In this exercise, you will react a thiol (R-SH) with a gold surface to form a self-assembled monolayer (SAM) of thiol molecules on the gold. The thickness of this layer is about 2 nm (nanometer). A molecular system like this with dimensions at the nanometer level is an example of nanotechnology. Molecular self-assembly is also the key mechanism used in nature for the creation of complex structures such as the DNA double helix, proteins, enzymes, and the lipid bilayer of cell walls. 

For comparison purposes, nanotechnology is defined to be less than 100 nm. Feature sizes less than 100 nm are likely to have life-limiting diffusion failure modes. The comparative size of a nanometer to a meter is the same as that of a marble to the size of the earth. The DNA helix has a diameter of 2 nm. The smallest bacteria (mycoplasma) have a length of about 200 nm.)... 

A nanometer (nm) is 10 m or 1 nm = 10 A. In terms of human parameters, the diameter of the double helix is 2 nm, bacteria are about 200 nm long. Another comparison that has been made is that the ratio of a nanometer to a meter is similar to that of a marble to the diameter of the earth. 

It is interesting to note that the requirement ot imdistorted helix ot cholesterics is analogous to the constant layer spacing requirements ot smectic liquid crystals. For this reason the concept ot permeation is also important in smectics, and to some extent their mechanical properties are similar. The "only" difference is the length scale of the periodicity a few nanometers in smectics and micrometers in cholesterics. Based on this analogy, Lubensky and de Gennes constructed a coarse-grained version of the continuum... 

The content of pure P-sheet conformation was determined to 34%, whereas the rest was either a mix of unordered/a-helix or a-helix/p-sheet domains. A detailed evaluation of the TERS data revealed that the amino acids Cys and Tyr were mainly present in P-sheet-dominated areas, whereas Pro was typically found in a-helix domains. Since Pro is known to interrupt P-sheet structures by means of its molecular structure, this is consistent with previous results and was found also with nanometer lateral resolution. 

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