In an attempt to avoid the work in front of me, I find it crucial to prepare for the Fall 2011 semester, and an interesting thought bubbled up while reading one of my Microbiology textbooks: what are the analog functions of a cell?
Digital versus analog centers on whether whatever you are measuring can take any value (analog) or whether it is limited to certain discrete values. Computers are digital because all of the information is a string of either 1’s or 0’s. A vinyl record is analog because the information is a series of grooves that could be any depth (0mm, 0.01mm, 0.02mm, 0.021mm etc).
In a cell, the sequence of DNA is clearly digital (its either A, C, T or G). So is RNA (A, C, U or G). So is protein (sequence of 20 discrete amino acids)*. But what would be analog information in a cell be? I am thinking in terms of metabolism, and if you could somehow ascertain the exact concentration of every metabolite in a cell, that *would* be information of a sort – it would tell you something about the state of that cell at that particular moment (dividing cells would have increased concentrations of DNA nucleotides, flu virus infected cells would have increased concentrations of RNA nucleotides, cells from the thyroid would contain the precursor molecules to thyroid hormones). The concentration of metabolites is definately a
discontinuous variable (1uM, 1.01uM, 1.011uM etc), so is that analog inforamtion? I am composting these thoughts as I think of different ways to introduce students to the cellular nature of life, what cells do etc, but mostly I am avoiding the work in front of me.
* – After I wrote this it occurred to me that while the information in the *sequence* of DNA, RNA & protein is digital, there is an analog side here too as the RNA, DNA or protein molecules can be present in differing concentrations and THAT is valuable information. In fact, we now put a heavy emphasis on the analog informatin in mRNA transcript levels to characterize cells or disease states. Gene expression chips only give you analog information