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Biotech Science

Digital DNA Circuits 157

Posted by michael from the synergistic-merger dept.
TheSync writes "ScienceNews has a story about digital DNA circuits. The circuits use proteins that activate or deactivate genes on the DNA for control. Since an inverter and an AND gate have been created, any digital logic circuit can now be done in DNA. Moreover, evolution can help make circuit elements work better. There is even a "databook" of BioBricks circuit elements and BioSPICE for biocircuit simulation."
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Digital DNA Circuits More

Digital DNA Circuits

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  • And, not (Score:2, Interesting)

    by Anonymous Coward
    But does this mean we can store data in DNA using hundreds of bases (latch), instead of a few bases directly?

  • Oh! (Score:2, Interesting)

    by Quasar1999 ( 520073 )
    So that's how the neuro-gel packs work in Star Trek... and all this time I thought it was crap!

    Seriously though... what's the delay on these things? Comparable to silica versions?

    • Re:Oh! (Score:5, Informative)

      by g4dget ( 579145 ) on Tuesday April 29, 2003 @03:10PM (#5837314)
      Transcription and translation happen at about 45 nucleotides per second in bacteria, meaning it takes at least a few seconds to get a signal through a genetic "gate" or "switch".
      • Transcription and translation happen at about 45 nucleotides per second in bacteria

        That sounded a bit low to be considering that some bacteria replicate every 20 minutes, so I did a google search. Most popular google report is 500 nucleotides per second in bacteria, plus some reports of specific bacteria running 1000 per sec.

        -

        • Re:Oh! (Score:3, Informative)

          by aqkiva ( 629658 )
          The original post of 45 nt/s is correct for transcription and translation (the speed of RNA polymerase and ribosomes). 1000 nt/s is for replication (the speed of DNA polymerase).

      • Re:Oh! (Score:5, Informative)

        by The_K4 ( 627653 ) on Tuesday April 29, 2003 @03:53PM (#5837711)
        Yes, but if you have several trillion copies of your program you can run them all in parellel. Think of cytography....you could make a bioprogram that's designed to find the 128 bit key. There's 2^128 possible solutions. So if you have a whole bunch of these 2^1000 bio-programs in a solution, you can quickly find the 128 bit key. Look here under DNA computing [computer.org] for an example of why this stuff is useful, even if it is slow compared to silicon.
        • Yes, but if you have several trillion copies of your program you can run them all in parellel. Think of cytography....

          There's a novel on this subject, "The Paris Option" by Robert Ludlam. Terrorists steal a DNA computer and use it to break all of our encryption codes and wreak havoc on the U.S. military and infastructure.

        • Re:Oh! (Score:3, Insightful)

          by g4dget ( 579145 )
          No, you are just confusing lots of issues. DNA computing has little to do with genetic networks. It's also unproven whether DNA computing can actually do anything useful.

          And while DNA is compact, 2^128 and 2^1000 are really big numbers. 2^128 is about 10^38, and 2^1000 is about 10^300. A pound of hydrogen has about 10^27 atoms, so even if you use one hydrogen atom per key, you need nearly a billion tons of hydrogen just to get 2^128 atoms, let alone a billion DNA molecules.

          All this attention from comp

          • "let alone a billion DNA molecules."

            Oops--that should have read "let alone 2^128 DNA molecules".

          • "There are interesting questions to be asked there..."

            I agree: Would it be illegal to kill (turn off) such a computer? Would it be illegal to overclock with controlled substances?

            In all seriousness, however, there are some pretty amazing things that could be done with a DNA-based computer. The fact that it is actually in base-4 rather than the traditional base-2 allows much more data to be stored along a given chain. (Yes, I'm aware that there are only 2 combinations of the 4 chemicals, but you can arr
    • This means mister checkov could have very well been saved by a device placed on his forehead during star trek 4... DUDE!!!

  • Huh? (Score:2, Funny)

    by blackmonday ( 607916 )
    This one wins my vote for absolute nerdiest post ever!

  • imagine that (Score:5, Funny)

    by g4dget ( 579145 ) on Tuesday April 29, 2003 @03:02PM (#5837254)
    And people have known about them only for, oh, a few decades [nature.com].
    • A lot of people are saying "Nothing new here, these are just gene feedback loops," "this will pale in comparison to the power of sillicon" and "when can I customise my own bizarre pet."

      They're missing the point.

      I think that the most exciting thing about this research thrust to make packages of genes that you can plug into a genome and expect to see it work is that it is concurrant with Stephen Wolframs's A New Kind of Science [wolframscience.com].

      Sure Wolfram claims to have invented everything from Mathamatica (fair enough)

  • but then... (Score:4, Interesting)

    by Tuxinatorium ( 463682 ) on Tuesday April 29, 2003 @03:03PM (#5837265) Homepage
    but then, that's not much more compact than a 90-nanometer transistor. Do you know how huge a polymerase protein is?

  • Motorola anyone??? (Score:1, Funny)

    by Anonymous Coward
    This sounds like an ad for Motorola
  • Does anyone know of any research into DNA computing and cryptography? I'd expect, given the massively parallel capabilities of DNA, it would be a very useful tool for a brute force attack...

    Imagine coding all possible keys as dna, mixing in the message, and pulling out the only possible and logical match -> your decrypt.

    Or am I just dreaming?

    Jw

    • Re:DNA computing and Cryptography (Score:4, Interesting)

      by rwiedower ( 572254 ) on Tuesday April 29, 2003 @03:09PM (#5837305) Homepage

      Even your body doesn't rely upon chemical reactions to accurately predict certain outcomes. Studies have shown that nerve fibers in your arm will often send a "the ball is coming" signal to your brain well in advance of the actual signal reaching your fingers. This sort of predicative function makes complex tasks like walking and talking much easier, but when it catches up to you (like when you fall on the bottom step of a flight of stairs because you forgot how many steps there were) you crash and burn.

      The point is, that chemical reactions are very slow. If they were faster, your brain (and your neurons in your arm) wouldn't have to guess. Because they're so slow they'd be very poor at brute force attacks, regardless of the sheer number of cells.

      So, yes, you're dreaming.

      • The point is, that chemical reactions are very slow.


        So run them in parallel. A billion DNA strands can fit on the head of a pin. More could fit in a beaker.
      • Actually this could be effective - bacteria are von neumann machines ;)
      • Actually, he is not dreaming. Chemical reactions will (and already have) yeild massive parallel computations. DNA oligamers have already been used to solve for the solution to path problems in graph theory. The trick is designing the system. That is the hard part. The theory is that chemical reactions can be used for parallel processing is ALREADY practice.
      • The point is, that chemical reactions are very slow. If they were faster, your brain (and your neurons in your arm) wouldn't have to guess. Because they're so slow they'd be very poor at brute force attacks, regardless of the sheer number of cells.

        In this case, it isn't really an issue of the speed of chemical reactions (which oftentimes are not slow at all - they can be nearly instantaneous). The electrical impulse that moves along each nerve is very fast, of course, but the slowdown occurs between nerv

    • Try this page [cs.ubc.ca]
  • they have a trade mark on digital dna i believe...i just just seem them getting their attorney's ready. they have to make money somehow! :)

  • Illuminate Me (Score:2, Interesting)

    by rwiedower ( 572254 )

    Okay, this may seem short-sighted, but if silicon circuits are so much faster, why not simply design silicon-to-carbon interfaces rather than try to redesign the wheel? Unless there's some level of functionality that's not applicable on the silicon side, I don't see why the results of a process couldn't be approximated. In the article, for instance:

    It's far easier to describe the schematics of these circuits than to build them for operation inside a cell. For instance, to hook up one gate to the next, th

    • Depends what you want to do. If you're looking for autonomous, self-contained agents, Si-C interfaces will be far to large and cumbersome to meet your mobility needs. If, alternatively, you want a sessile colony of living front-ends to an electronic circuit, synthetic ion channels might be useful as an interface.

    • Re:Illuminate Me (Score:2, Interesting)

      by Mr. Spectre ( 669558 )
      Okay, this may seem short-sighted, but if silicon circuits are so much faster, why not simply design silicon-to-carbon interfaces rather than try to redesign the wheel? If the end result is accomplished simply by having the right protein the right place at the right time, why not build the circuit in silicon and simply train the cell to produce the appropriate protein based on the result of a calculation?

      They are hacking the instructions written the code that cells already understand. This might allow f

      • Re:Illuminate Me (Score:2, Insightful)

        by rwiedower ( 572254 )

        I wasn't saying the interface would solve the problem. I was saying that if I designed a cell to respond to an external stimulus with a certain protein production, I'd have a handy interface. Instead of building a cell to light up in the presence of a complex chemical compound, I could then simply have a cell send a protein to a circuit which could then send a signal to a led. Or, vice-versa, I could program a complex series of actions into a processor which would then interface with said S-2-C cell which w

        • are your problem. You might be able to use carbon nanotubes, but otherwise I dont see anything that could not rupture the cell and connect to a digital device at the same time. If we could build a silicon chip that could detect the presents of proteins that would be nice, but (pardon this comment if I'm wrong) I don't know of any chip/gate that can change states at the presents of a protein like these cells can.

    • Re:Illuminate Me (Score:2, Insightful)

      by ciroknight ( 601098 )
      There are applications of this FAR beyond those of silicon. What if you designed a circuit to detect the presents of certain viruses? You could make chemical/biological weapon detectors the size of CELLS! Also, think of what it can give us in a way of examining solutions to problems in our bodies.. you could design circuits to output certain chemicals/protiens when certain chemicals are in our blood stream. We could build cells that help filter out cancerous elements, PRODUCE INSULIN so that people woul

      • Wasn't this what nano-technology promised us years ago? We would all have tons of nanites roaming through our bodies, cleaning up the arteries and destroying cancerous cells. So far though, little concrete has been developed.

        I'll believe it when the applications actually arrive. And unlike nanites, these cells depend upon chemical reactions...I'm not sure I'd trust someone to inject tons of living cells into me the same way I'd trust them to inject tons of non-living machines into me.

        • The beauty of it is, it wouldn't need to be tons, and they wouldn't have to be injected neccisary. And besides, every day walking through your house you intercept hundreds of thousands of airborne bacteria. This is nothing new to us.

          The other advantage is unlike nanites, these things are very temporary. Our immune systems would nuke them pretty quickly, within a few hours in most cases. But for uses like insulin production, you'de have to develope one that was resistant, or actually lived somewhere e

  • Death.. (Score:3, Funny)

    by Anonymous Coward on Tuesday April 29, 2003 @03:05PM (#5837280)
    So, now will death be refered to as a power outage?

    • Re:Death.. (Score:2, Funny)

      by hesiod ( 111176 )
      > So, now will death be refered to as a power outage?

      Well, it sort of is. As I understand it, death is usually just a lack of oxygen to the brain (explains why guillotine victims seemed to be alive a few moments after being decapitated -- there was still blood/oxygen/power in the head, feeding the brain.

  • [insert supreme being/philosophy etc.] called... (Score:5, Funny)

    by Dutchmaan ( 442553 ) on Tuesday April 29, 2003 @03:07PM (#5837292) Homepage
    He wanted to remind you that he has held the copyright for DNA for billions of years now..

    He's been in contact with his lawyers and is tallying your bill as we speak.

  • Could you program these bacteria… (Score:5, Funny)

    by Anonymous Coward on Tuesday April 29, 2003 @03:11PM (#5837327)
    ... to play the game of life?

  • Self-improving circuits (Score:5, Interesting)

    by 16977 ( 525687 ) on Tuesday April 29, 2003 @03:13PM (#5837346)
    The most interesting thing about this announcement is that this guy has been able to use evolution to improve his circuits. I don't expect molecular computers to surpass electronic computers, at least right away -- although they could theoretically perform faster than electronic computers in the short term, any advantage is offset by the time needed to convert the information to human-readable form (by finding and correctly reading the DNA sequence). As the article says, it's better to take advantage of the fact that you can "work with" bacteria. But if DNA computers could repair and upgrade themselves, they would have an advantage that electronics currently does not have. Electronics already is under intense artifical selection, and it can reproduce itself after a fashion, but unlike copper and aluminum, DNA computers can be randomly mutated, and the close homology between computers ensures that some of those mutations will be beneficial.

    • DNA, maybe. DNA is fairly good at reproducing without errors. RNA, on the other hand, isn't that good with errors, but is much quicker. (Ask any virus.)

      My thought is this: as soon as the process becomes complex, errors introduced into each cell could produce vastly different results. And the debug process would be tortuous. There'd be no guarantee that a single mutation couldn't bring down the whole system.

      • DNA, maybe. DNA is fairly good at reproducing without errors. RNA, on the other hand, isn't that good with errors, but is much quicker. (Ask any virus.)

        DNA and RNA don't replicate themselves, they need the help of enzymes called polymerases [weihenstephan.de]. These biological machines unwind the template DNA or RNA strand and create a complementary copy (A pairs with T, G with C). Along with the template reading and synthesis domains, there is also a proofreading domain, checking to ensure that the right match has been mad

    • The problem I see with this is that we assume that the circuits that implement our desired function will be selected for. What if the circuit can be biologically successful without implementing the desired result. After all, we haven't figured out the question to that 42 question yet.
    • First of all, this is just an issue of genetic algorithms, which don't require you to explicitly have a logic circuit coded in DNA -- there's many other analogous ways of "evolving" software or circuits.

      Secondly, they do come up with very interesting results (sometimes), but often these results are not really what you'd want. I can't seem to recall details (if anyone has a reference I'd appreciate it), but I recall about a decade ago someone evolved a timing circuit that used something like 20% fewer gate
    • FPGA.

      They can do the same, auo mutate, compare circuits topology using the game of life rules and "automatically" reconfigure and evolve to compare their results to an etalon measure.

      => Seem to remember a FPGA test where the goal was tone recognition. The FPGA was programmed to try and get a wave analysis and recognition tested against set rules.

      After X generation, not only did the processor perform the deed asked, but had modified it's gate in a way even the engeneer that designed it didn't envision,

  • New female DNA logic circut states (Score:5, Funny)

    by Timesprout ( 579035 ) on Tuesday April 29, 2003 @03:15PM (#5837371)
    YES
    NO
    MAYBE

  • Great (Score:2)

    by grub ( 11606 )

    The DNA circuits will be used in mainstream computing hardware.. The DNA wired computing hardware will become Skynet.. The DNA wired computing hardware that becomes Skynet will become self-aware.. You know the rest of the story.

    Where's my tinfoil hat?

  • Don't know how 'wow'-ing this really is... (Score:4, Interesting)

    by Necromancyr ( 602950 ) on Tuesday April 29, 2003 @03:20PM (#5837416)
    Reports of this sort have been coming out for a few years now - basically, all they are doing is a controlled induction of a promoter. It's nothing amazing. Chaining one promoter to express another promoter ad infinitum (or to restrict expression) is already done in nature and used extensively to create transgenic cell lines, bacteria, etc. Hell, they've already developed means to do basic computations with DNA that are more applicable/advanced then this in some respects.
    • It has always amazed me that a mere ~60 years ago computers the size of buildings were doing very simple calculations, and the people marveled at this incredible technology....

      What is DNA going to be doing in another ~60 years?
    • This article was designed to amaze people that don't know anything about genetic regulatory systems. The hugely complex bodies of all organisms are "computed" by the the genes of the original fertilized egg. there are plenty of examples of genes that switch other genes on and off, and AND and OR are all over the place.

      More interesting are the abstract pattern creation systems. Think about the following example.

      Fly legs have precursors in maggots which are flat disks. The disks are concentric circles of pr
  • Does this mean that a new bread of modern inovative programming languages will be needed? I am sure that most expirenced programmers would definatily like to do something differently to make the development process more efficient, and faster.

    Any suggestions on what you would like to see if a new language was developed for this platform?

  • proteins (Score:2, Interesting)

    by lazira ( 651928 )
    Have there been studies in alternate programming methods/languages for DNA, like there were for quantum computers? DNA logic doesn't need to be sequential- each protein can affect many things at once. It seems rather unwieldy to try to apply conventional logic building blocks, as each gate would require a unique protein and inhibitor- you can't use the same block twice.
  • ...engineers are starting to program microbes to carry out behaviors that nature never dreamed of. // Eventually, the goal is to produce genetic 'applets', little programs you could download into a cell simply by sticking DNA into it, the way you download Java applets from the Internet.

    Not to stir up the scare-mongers and doom-sayers but that is one huge can of strangely colored worms.

    Combine this w/ personalized medicine and you might live to be 600, albeit going to the doctor every week for a Ser
    • How do we stamp "FDA approved" on these little buggers?

      No problem: just make a few tweaks to the Palladium specifications so MS + CIA own your body in addition to your computer, documents and household appliances.

  • A hefty airtight coolance case to keep your computer circuits from molding.
  • Gives a new meaning to 'my computer died'.

  • I found particularly enlightening the apparent similarity between Java applets and programmable DNA:

    "Eventually, the goal is to produce genetic 'applets', little programs you could download into a cell simply by sticking DNA into it, the way you download Java applets from the Internet," says Timothy Gardner, a bioengineer at Boston University.

    While it would have been better if it resembled something better supported in open source, it is a relief that it is not modelled after the patent-encumbered CLI-b

  • Grey goo theory? Super sperm? (Score:4, Funny)

    by macshune ( 628296 ) on Tuesday April 29, 2003 @03:36PM (#5837567) Journal
    Will Bill Joy's "grey goo" theory turn out to be just a bunch of DNA-computer-packin' malevolent super sperm?

    Will women have to worry about guys with DNA-computer enhanced sperm, so unprotected sex could mutate a woman into a ninja turtle?

    Will I be able to code myself urine that tastes like apple cider and poop that tastes like swiss chocolate?

  • Teletubbies not so far fetched... (Score:4, Funny)

    by Billy the Mountain ( 225541 ) on Tuesday April 29, 2003 @03:37PM (#5837577) Journal
    If you could embed this into human cells, I bet you could convert my stomach into a 1280 X 1024 display!

    BTM

  • NOT gate (Score:4, Informative)

    by Bowling Moses ( 591924 ) on Tuesday April 29, 2003 @03:39PM (#5837592) Journal
    Sounds similar to work being done by the Arnold group at Caltech. They've apparently (haven't read the article yet) made a NOT gate using directed evolution. They're more interested in developing and applying the directed evolution technique than in biological computers, it seems. Lab website's here [caltech.edu]. And the lab website's got their own articles available for free in .pdf form. Screw you, Elsevier!

  • Spaghetti Code (Score:5, Interesting)

    by Obiwan Kenobi ( 32807 ) <evan@@@misterorange...com> on Tuesday April 29, 2003 @03:40PM (#5837606) Homepage
    I was listening to NPR the other day which focused on DNA as a computer.

    The guy interviewed correllated the DNA genetic map to spaghetti code, a programmers worst nightmare. Apparently all through the genetic make-up of our bodies are "fuction calls" (to put it simply) and pathways that reference other calls and other pathways, over and over upon itself for a hundred million lines.

    Its not the listing of the GTAC code (ie, genetic map) that's really necessary. Though of course it plays a part. Its the understanding of such code, what it does and what it controls, where power lies.

    The guys interviewed all guessed it would be a hundred years or more before we began truly understanding what "functions" do what in the DNA strand and how it affects the organism in question.

    Food for thought.
    • So, what's the codon for "goto"? Do we know that one yet?
    • Java bytecode also doesn't look terribly appealing in a text editor.

      I wonder if we could decompile our VM and reverse engineer DNA back into it's original source code.

      I'm guessing it's something like LISP

    • The article link (Score:3, Insightful)

      by Obiwan Kenobi ( 32807 )
      Is right here [npr.org]. Highly suggested reading/listening.
    • The guys interviewed all guessed it would be a hundred years or more before we began truly understanding what "functions" do what in the DNA strand and how it affects the organism in question.

      Bad guess. If you check google there are plenty of articles about specific projects on track to build a minimal synthetic cell within a few years.

      It will be a while before we work out the functions and subtlties of all genes, but we're off to a decent start.

      -
    • The guys interviewed all guessed it would be a hundred years or more before we began truly understanding what "functions" do what in the DNA strand and how it affects the organism in question.

      These developers, they never document anything. Would a few comments really have been all that difficult?! ;-)
    • Spaghetti code can work better. Just look at the more successful Corewars [sf.net] programs, especially the evolved ones - they go and modify their code in mid-run, the result being much greater efficiency (and it's more compact, to protect against attacks (or mutations)).
    • A big question is though:
      Can we use these basic building blocks to help improve our knowledge base of biology? Could this be used as a link to help more efficently understand more biology? Could there be a way of coding biological structures to communicate with a more typical logic-program? The logic-program could help output data in a form we're more accustomed to.

    • Re:Spaghetti Code (Score:2, Insightful)

      by DocDendrite ( 666208 )

      The guy interviewed correllated the DNA genetic map to spaghetti code, a programmers worst nightmare. Apparently all through the genetic make-up of our bodies are "fuction calls" (to put it simply) and pathways that reference other calls and other pathways, over and over upon itself for a hundred million line

      This seems a little strange to me. I am a fourth-year PhD student in Molecular Biology and I see a lot of Biology misinformation on slashdot.

      What the NPR interviewee said does appear true. Howeve


  • After looking at the article for a couple of minutes, a couple of things are clear to me:

    1) being able to encode logic circuts using DNA != being able to program nano-size virus-like bio-bots to follow your instructions. The "processors" that drive life in virii, bacteria and cells do not follow instructions of this sort. Sure, you might be able to produce an organic computer that can 'run the program', but it won't be alive, it won't reproduce and it'll be a hell of a lot slower than a similar computer
    • Radio Shack might be a good subject for such a stupid trollery, except that even the most heinous trolls are disgusted by Radio Shack's utter lack of any sort of electronic or computer equipment. This is offtopic, flamebaitish, and perhaps even actionably libelous on my part so get your -1 mods ready, but Radio Shack is incredibly worthless, misnamed and quite likely 'gay' in the literal homosexual sense of the word. They remind me of those ghetto beauty salons you see where the proprietor has no business s

  • Keep working (Score:3, Insightful)

    by smittyoneeach ( 243267 ) on Tuesday April 29, 2003 @05:05PM (#5838222) Homepage Journal
    I don't think we'll have serious applications in bioware in the next decade.
    The sequencing work done to date is phenomenal. Not trying to sell anyone short. However, the complexity when you move from the genome to the proteome can be fairly described as staggering, so I'm weighing in on the conservative side on this one.
  • Here's a nice salon.com (fictional) story about this topic, fast forwarded and given a bigger picture [salon.com].
  • Calories per second?
  • I had a look at the "BioBricks" site - anyone out there who does molecular biology work should do the same if you're looking for a laugh.

    It reads rather like a treatise on basic cloning written by someone who had a look through Maniatis (Sambrook for the newbies) and pretty much understood most of it.

    The plasmids with "ampecillin" resistance genes, and their MCS with an "Echo RI" site, good lord...

  • Origins of this stuff (Score:4, Informative)

    by WillWare ( 11935 ) on Tuesday April 29, 2003 @07:29PM (#5839256) Homepage Journal
    Tom Knight and some other MIT people were talking about this kind of stuff in 1996-97. This was the same group interested in amorphous computing [mit.edu] at the time. They saw it all as one big research agenda, and amorphous computing fell under the DOD funding umbrella for autonomous battlefield surveillance widgets.

    These guys were poking around with some genuinely interesting ideas. Their idea was that if you relaxed the requirements on manufacturing quality, you could make nodes that were super-cheap with a modest (but today-considered-unacceptable) failure rate. They set forth a collection of programming axioms that treated a sea-of-nodes as a continuous computational "gunk". Very cool stuff.

  • Oh, the irony... (Score:4, Insightful)

    by nickgrieve ( 87668 ) on Tuesday April 29, 2003 @07:55PM (#5839429) Journal
    In the course of her work with Watson and Crick, Rosalind Franklin had to do a serious amount math by hand (Patterson analysis to create Patterson maps). Later, after her work on DNA she was forced to hire a computer (an 18yr old girl) to do the leg work on the data she gathered on the Tobacco Mosaic Virus.

    Today I read here http://www.sciencenews.org/20030426/bob11.asp (Computer circuits made of genes may soon program bacteria)

    "Silicon circuits perform complex operations using a handful of simple components known as logic gates. Genetic- circuit engineers are now building the same devices inside cells."

    I wonder, what she would have thought, to know that very thing she was studying could some day be used to do the math that took up so much of her time.
  • I'd started to compose a 'funny' about computers that worked about 8 orders of magnitude slower than the calculator in my mobile phone and mutated to give unreliable results at the end of the guarantee period, then looked at the article.

    This isn't (yet?) an attempt to build a bio-computer (although from the article they've apparently already reached the Blinkenlichts level: The result was a population of gently twinkling cells like flashing holiday lights, Elowitz says. "It was very beautiful," he says).

  • One thing they didn't mention is that Gene circuits can not only exhibit bistable behavior (bits), but multistable behavior (trinary, etc). Because chemical species exist in concentrations and not 'on' or 'off, there's quite a bit of additional complexity that can be utilized to perform added functions.

    Differentiating stem cells in the body take a signal (concentration of a chemical species) and differentiate into different cell types (more than two different cell types).

    Sometimes, it's like an 'if then'

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