3-D Optical Memory Storage In Bacteriorhodopsin
With the growth of Information over last few decades, demands for its efficient storage and faster processing has reached new dimensions. The need of the hour seems to be development of high capacity secondary storage devices as well as faster processors. The RAM used in most computers is the same type of memory used several years ago. The limit of increasing the density of RAM has already been reached. These limitations are more economical than physical. Presently RAM modules vary in capacity from a few hundred kilobytes to about 64 Megabytes. Anything greater than this range is both expensive and rare. . In comparison a 5 cubic centimeter block of Bacteriorhodopsin,( a light transducing protein in purple membrane of salt marsh archeon Halobacterium Salinarum ) studded in a polymer matrix could theoretically store 512 gigabytes of information. Moreover Bacteriorhodopsin modules could be run 1000 times faster meeting the demands of both speed and power of future digital computers. Also the present secondary storage devices store one dimensional (serial) information in a 2D plane which to a greater extent limits the memory bandwidth. However 3D memory devices using Bacteriorhodopsin modules store 2D information (Bit planes) throughout a volume with information partitioned in binary planes that are stacked in third dimension. One memory operation on entire bit plane, gives rise to tremendous memory bandwidth.
This has opened up gates for what are the major areas of improvements in purely electronic computers:
1) Ultra dense multi tetrabit memories (of the order of 1 Tb/cm3 ).
2) Highly parallel processing.
3) Nearly real time write and retrieval rates.
4) Data retention for longer time.
Russian scientists, under the leadership of the late Yuri Ovchinnikov, were the first to recognize and explore the potential of bacteriorhodopsin through their projects, termed ‘Project Rhodopsin’, which were intended only for military applications. Soviet military was able to make microfiche films out of Bacteriorhodopsin, known as “Biochrome”.
➢ About the molecule
Bacteriorhodopsin (bR) is a light transducing protein dye found in purple membrane of salt marsh archeon Halobacterium Salinarum . This membrane serves a a protection against harsh environment of salt marshes where the salt concentration is six times the ordinary sea water and temperature ranges around 150 degree Fahrenheit . bR allows Halobacterium Salinarum the ability to convert light energy to a metabolically useful form when conditions are unfavorable for aerobic respiration. It does so by switching to photosynthesis by acting as a proton pump, sufficient to sustain respirative oxidative phosphorylation.
Structurally, it is ̴̴̴26 KD (400nm*400nm*500nm) composed by a sequence of 248 residues arranged in 7 trans-membrane α-helices and 1 β-sheet .It also contains a retinal chromophore linked through a protonated Schiff base to Lysine-216.This cromophore gives the protein photoactive properties that on light excitation of certain wavelengths generates different isomerization states. The photocycle of bR consists of these various isomeric states.
➢ Photocycle of bR and data recording principle
bR consists of two different paths of isomerization reactions. The main photocycle consists of the left hand side of the figure. In course of studying the material a branching reaction was identified marked as P and Q states. The first path starts at the state called bR which is the most stable state of the protein. Green light induction with a wavelength of approx... 600nm triggers the first chain reaction that causes the protein to change its isomery in six different states.. From bR the following states are K, L, M, N and O. If only blue light is...
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