What Kind of Information Does DNA Contain?

like the term evolution the term information has more than one definition and there is more than one type of information that might be present in living systems shannon's theory of information is something that you might be familiar with if you're a an engineer or a software designer or a mathematician claude shannon was a mathematician and computer innovator in the in the late 1940s after world war ii and he developed a mathematical theory of information he had a really interesting uh intuition that underlay this this idea he wanted to be able to quantify how much information was in a in a series of symbols along a communication channel and his his intuition was that that information was related to the reduction in uncertainty provided by that sequence of symbols so for example just to illustrate the intuition if i tell you that in november in seattle it's going to rain people who live in seattle know that i haven't actually reduced much uncertainty it always rains in seattle so that's not a very informative statement at least to someone who lives in seattle if i tell you however the outcome of a closely contested baseball or football game that you didn't have the chance to to watch i have reduced a lot of uncertainty and therefore i've given you an informative statement this was shannon's basic intuition information is related to the reduction in uncertainty the more uncertainty reduced the more information transmitted now shannon went beyond this information or this intuition rather to quantify this relationship for example if i were to take a coin and flip it there are two possible outcomes there is the proverbial head and the proverbial tail you've got two different possibilities but if i take a die and i roll it i've got six possible outcomes so in the case of the die once one outcome is fixed i've eliminated five other possibilities and therefore i've reduced more uncertainty than i have in the case of the coin flip in the coin flip i have eliminated one possibility when i've elected another only eliminating one out of two possibilities conveys less information reduces less uncertainty notice that the amount of information or the amount of reduction of an uncertainty is inversely related to the probability of the event that occurs in the case of the die there were six possibilities when one is fixed i have eliminated five other possibilities but the probability of that one being fixed was one in six i've eliminated more uncertainty elected more information in the case where the event itself was more improbable in the case of the coin i've only got two possibilities so when one of the possibilities is fixed i've eliminated one other possibility but the probability of that one being fixed was only one out of two so in the case where i have eliminated less uncertainty produced more information it's been the case where there the probability of the event was smaller so die smaller probability more information conveyed coin less information conveyed less improbable so the idea here is that information is inversely related to the probability of the event which excludes other possibilities now what's all this got to do with biology well first of all we need to understand that in shannon information there's a nice equation and that equation is written in that it can it connects these ideas of improbability and information the classic shannon equation is the information equals log to the base the negative log to the base two of the probability of the event so the more improbable the event the higher the information measure the less probable the lower the information measure now let's ask again the question what does this all have to do with biology well it is interesting because the coding system in dna does lend itself to a mathematical analysis of the kind that shannon gives because at each side along the dna strand there are four possible four possibilities you have the four different nucleotide bases adenine guanine thymine and cytosine a t c and g so any time one of them is fixed it eliminates three other possibilities and therefore there's a calculable amount of shannon information conveyed at each site along the growing dna strand but there's also a catch because with shannon information you can't determine the difference between a functionally specified arrangement of characters or a meaningful arrangement of characters and an unspecified sequence one that is essentially random or which has no meaning or no function shannon just gives you a measure of what's called the information carrying capacity it doesn't tell you whether the information in the string of characters is meaningful or functional or not let me illustrate with these two strings of characters the the top string is essentially something that could be typed by monkeys at a typewriter as far as we know it's gibberish it's just a series of characters that might be randomly produced the bottom spray string however is something that we recognize right away as having meaning the poetic phrase time and tide wait for no man the top string in information sciences is often referred to as a complex string it's complex because it's not rigidly repeating it's not abc abc abc abc over and over again that kind of a string would be called a redundant or orderly string of characters a complex string is one where you can't discern a repetitive pattern and therefore it's complex or also we could think of it as highly improbable but the very bottom string the time and tide weight for no man is also complex there's no originally repeating pattern there there's no abc abc abc but in addition to being complex it also is specified that is to say it has the arrangement of the characters matters in order to allow it to perform a communication function or in order for it to convey meaning so the key point here about shannon information is that shannon's measure of information carrying capacity can't distinguish between the functional and the non-functional strings of characters so back to biology what kind of information is in dna well the answer is actually both there is a quantifiable amount of shannon information but the information in dna is also functional it directs the construction of proteins and protein machines francis crick who was well aware of the developments in the information sciences in the field of information theory developed by claude shannon shannon was developing his ideas in 1947 1948 1949 crick had been a code breaker in world war ii and so he was well aware of these developments but he was also well aware of the limits of shannon's information theory and so crick very carefully clarified what he and watson meant by information in the case of dna in 1958 he wrote that by information i mean the specification of the amino acid sequence in the protein or he said i mean by information he said information here means the precise determination of sequence either of bases in the nucleic acid or amino acid residues in the protein in other words he was saying that the information in dna is specific the the character the arrangement of characters matters in that it allows the molecule to perform a communication function so the kind of information we're talking about in dna is not just shannon information not just the information in the mathematical sense of information carrying capacity it's not just something related to improbability the characters are improbable but they're also specified or arranged precisely in order to perform a function so the kind of information we're talking about in dna is a much richer definition of information than the mere mathematical definition of information provided by claude shannon in fact it's much more similar to the kind of information that we use in everyday life whether we're using english text or computer code webster's dictionary defines information in the following way it defines it as the attribute inherent in and communicated by alternative sequences of arrangements of something that produces specific effects the alternative arrangement of something in case of english would be alphabetic characters and those produce a specific effect if they're arranged properly they produce a communication effect the information in dna turns out to be that kind of information and in my book signature in the cell i therefore make a distinction between shannon information and his various synonyms like information carrying capacity or improbability of arrangement on the one hand and specified information or specified complexity or functional information which would all be synonyms for shannon information plus function or meaning so the kind of information that we have in dna and that is similar to it is exactly the same in this in the theoretical sense in terms of these two categories of improbability plus function as the kind that we use in ordinary human language that is to say the kind of information present in dna is also a striking appearance of design because the kind of information that we use functional or specified information is always the product of a mind now this has actually been recognized this striking appearance of design by none other than richard dawkins himself he said that the machine code of the genes is uncannily computer-like that apart from differences in jargon the pages of a molecular biology journal might be interchanged with those of a computer engineering journal that the information in dna is like machine code in that it's improbable but also functional it performs a communication function bill gates has amplified that observation saying that dna is like a software program only much more complex than any we've ever created so what explains the origin of the functional or specified information in dna as dawkins and gates imply this kind of information the kind of information in dna exhibits a striking appearance of design what explains this striking appearance does natural selection and random mutation or some other undirected material process in the next several sessions we'll examine exactly this question because it's the question that's at the heart of the question of the origin of life we've seen it to explain the origin of new biological function to explain the origin of life in the first place you need lots of new proteins and those proteins are built from the information stored in the dna molecule so we want to know where does that information come from what explains that striking appearance of design for now i'd like you to read chapter four in signature in the cell and especially focus on pages 84 through 99 which discussed this whole question of what kind of information is present in dna

Channel: Discovery Science

Views: 28,087

Keywords: science, philosophy, biology, evolution, Darwinism, neo-Darwinism, human origins, science and faith, intelligent design, Discovery Institute, Charles Darwin, darwin's doubt, Stephen Meyer, Evolution News & Views, Michael Behe, William Dembski, John West, Darwin's Black Box, Privileged Planet, dna, origin of life, information, claude shannon, digital

Id: Qv95bW6V5uA

Length: 11min 54sec (714 seconds)

Published: Tue Aug 03 2021