Digital-to-Analogue Converter in the Cell points to Design
Digital-to-Analogue Converter in the Cell points to Design
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4082330/
Excerpt: "Cells must coordinate responses to many stimuli, including signalling cues from other cells, the extracellular matrix, hormones and active compounds. As they are subject to feedback control, these response pathways are usually ‘on’ or ‘off’ in nature. By contrast, transcriptional changes can be ‘dialled’ up or down and provide a composite response to multiple inputs over time. In line with this, signal transmission to chromatin can be compared to a digital-to-analogue converter (DAC) that takes ‘on’ and ‘off’ signals and converts them into a continuous output that can vary in amplitude over time. We speculate that histone tails may function in this way, acting as a site that stores signals and integrates them to regulate the transcriptional programme. Indeed, the pure density and variety of post-translational modifications on histones suggests that they are uniquely placed to act as signal integration devices.
Histone modifications work in combination, which adds to the diversity of outputs that they might facilitate. Crosstalk between histone modifications occur in cis and trans, by: influencing the binding of reader molecules to adjacent residues; precluding or recruiting enzymes that modify additional sites; or through combined effects on complex docking (termed ‘multiple site display’). Although the underlying mechanisms are not fully understood, the modification landscape can be fully or partially maintained throughout replication, allowing past signalling events to influence the current state of transcription. As a result, the transcriptional output of a single gene over a time course, or even over the life of a cell, follows a continuous wave pattern that can be dialled up or down, but that differs from the inputs received at any specific time point. Circadian gene expression is one example of this, whereby chromatin surrounding the CLOCK gene promoter is methylated, acetylated, then deacetylated to control fluctuations in the amplitude of CLOCK gene expression over a 24-hour period. Thus, histone tail posttranslational modification has all the features of a ‘storage and output’ device for epigenetic information. Nevertheless, it is ill defined how long a signal can be stored on chromatin. In addition, it is still largely unknown how the chromatin landscape is preserved during DNA replication and cellular division. Thus, determining the variables that define the longevity of marks on histones is critical for understanding the storage capacity for these marks."
My comment: CD player is a nice example of a device that needs a DAC, digital-to-analogue converter for the player being able to convert digital data to analogue format. A lot of research and design were needed before the standard for proper information handling was established in 1980. This kind of complex information protocols don't appear by chance or accident. They need perfect design. That's why the theory of evolution is the most serious heresy of our time. Don't be deceived.
