Wednesday, 30 July 2014

The most energy efficient memory

My translation into English from here.

DNA is the most energy efficient memory system known. DNA molecules store genetic information for all terrestrial life without exceptions. DNA is a polymer that has a double-helix with a step of 34 Å and a diameter of 20 Å. The two strands are connected by pairs of special chemicals called bases in intervals of 3.4 Å. The sequence of the base pairs determines the genetic information. Since DNA uses only 4 different types of base, each pair codes up 2 bits of information. This corresponds to an information density of ~1021 bits/cm3 (cf. information density of the human brain is just ~107 bits/cm3). The total volume of information in human DNA is ~108 bits. Interestingly, only about 10% of it is genetic information per se. In other words, only a tenth of it is a description of the structure and composition of humans or, more precisely, the «recipe» of the chemical synthesis of the human body. The remaining 90% accounts for the «administrative apparatus» that controls the transmission of genetic information. A comparison of the relatively small volume of human genetic information (~107 bits) with the human brain memory capacity (~1010 bits) leads to the curious conclusion that our experience greatly exceeds our heredity. It is also worth noting that the amount of genetic information in the simplest living thing, a virus, is only a few hundred times less than that in humans. The transmission of 1 bit of information stored in DNA requires about 0.2 eV, which is approximately 10 times greater than the normal temperature T = 300 К. Consequently, energy-wise as an information storage system DNA is close to an ideal one. Most probably, the extra order of magnitude in terms of energy cost ensures reliability of information transmission and is a measure of defence from thermal fluctuations. Therefore DNA ensures a practically possible minimum of energy cost per bit of information, in the presence of thermal noise.
See also my note here.

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