They read science articles, they just don’t understand them


But that doesn’t stop them from misinterpreting them! Here’s a classic example of Evolution News & Views completely missing the point of an article to claim it supports their beliefs about junk DNA.

I am so punchy and tired today that I wrote out a script. I had to. So transcript below the fold:

Hey, friends —

I got a question in my email, asking me a simple question…or maybe not so simple.

May I please ask you a last question? It is regarding an article I read recently. Intelligent Design proponents often use “junk DNA” functions as evidence for ID. I know that they are dishonest and advocate nonsense, but if you have time to have a look at the article below, may I ask for your opinion?

Caltech Finds Amazing Role for Noncoding DNA

I’m reading it and realized that the Discovery Institute was pulling an Otto. You know what I mean, the assassin in the movie A Fish Called Wanda, who was so incredibly stupid yet also pretentious, thinking he was an intellectual. You may recall the exchange:

Wanda says, “you think you’re an intellectual, don’t you, ape?”
Otto replies, “Apes don’t read philosophy!”
Wanda fires back with “Yes, they do, they just don’t understand it!”

That’s my summary. The Discovery Institute reads papers in Cell, they just don’t understand them. They ought to be embarrassed, if they weren’t so shameless.

There’s a problem, though. I have to provide a fair bit of technical background, so you can see what’s wrong with their take. They rely on that — they provide a bunch of complicated technobabble and emphatic confidence to make you think they’re super smart. Don’t be fooled!
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This particular article is titled “Caltech Finds Amazing Role for Noncoding DNA”; it’s a summary of a real, genuine science article published in the journal CELL, and what it’s doing is taking a legit science article and putting a creationist spin on it. It’s not clear who wrote it, but whoever it was didn’t actually understand the article. Here’s the introduction:
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Scientists at Caltech may have sounded the final death knell for the “junk DNA” myth. If only Dan Graur had known this years ago, it might have saved a lot of wasted rhetoric. ENCODE, readers recall, found that 80 percent of the genome is transcribed, even if only a small part codes for proteins. The functions of those non-coding regions were only hinted at. Now, the windows are opening on organization so all-encompassing for all those non-coding RNA transcripts, it is truly mind-boggling what goes on in the nucleus of a cell.

This is very strange. What the Discovery Institute article is is yet another attempt to debunk the idea of junk DNA, but the CELL article is not about junk DNA, and says nothing relevant to the creationist arguments about junk DNA. For some reason, creationists detest the idea that not all DNA has a specific function, and I’m not certain why. After all, their designer can do anything, why not just say that He intentionally left lots of room in the code, for expansion, maybe? Why not just call it the white space around the important content? Call it the artistic filigree He put there because He, in his unknowable ways, found it beautiful? It really would be that easy. But instead, they have to insist that it is all biologically functional.
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It’s almost as if they fear we might notice that their sacred holy books are maybe 5% good art and humane advice, and 95% flaming demented useless inconsistent junk, too.
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They do love that awful ENCODE study, which claimed that at least 80% of the genome was functional by an odd definition of functionality that no one accepts. The ENCODE studies argued that any bit of DNA that was transcribed into RNA counted as functional, no matter how short or rare it was, and ignored the possibility of spurious transcription. There are very few biologists who accept that nonsensical idea, but the creationists ate it up. If you mention junk DNA to them, they immediately bring up ENCODE in a kind of spastic kneejerk reaction.
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They also have a special loathing for Dan Graur, who has been particularly eloquent and historically literate in his arguments against every scrap of the genome being functional. There are limits to how many genes there can be based on the mutation rate and the ability of recombination to purify deleterious alleles — we’ve known since Haldane and Wright that humans ought to have approximately 20,000 genes, as confirmed by the human genome project, and that making any greater proportion of the genome functional would impose an excessive genetic load on the species. It is mathematically impossible for the claims of the ID creationists to be true.

But now they’re claiming that they’ve got a Graur-killer paper in their hands. It’s almost embarrassing how irrelevant this paper is to their claim.
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So here it is, “RNA promotes the formation of spatial compartments in the nucleus” by Quinodoz and others.

RNA, DNA, and protein molecules are highly organized within three-dimensional (3D) structures in the nucleus. Although RNA has been proposed to play a role in nuclear organization, exploring this has been chal- lenging because existing methods cannot measure higher-order RNA and DNA contacts within 3D structures. To address this, we developed RNA & DNA SPRITE (RD-SPRITE) to comprehensively map the spatial orga- nization of RNA and DNA. These maps reveal higher-order RNA-chromatin structures associated with three major classes of nuclear function: RNA processing, heterochromatin assembly, and gene regulation. These data demonstrate that hundreds of ncRNAs form high-concentration territories throughout the nucleus, that specific RNAs are required to recruit various regulators into these territories, and that these RNAs can shape long-range DNA contacts, heterochromatin assembly, and gene expression. These results demonstrate a mechanism where RNAs form high-concentration territories, bind to diffusible regulators, and guide them into compartments to regulate essential nuclear functions.

It’s not light reading. There’s a lot of quantitative molecular biology, and detailed analysis, and I’ll be honest, MY eyes glazed over here and there in the manuscript. To distill it down to the important points, though, they’re saying a couple of things. One, nuclear DNA is organized and shows a specific functional arrangement. This is not entirely new — I was reading about the 3 dimensional structure of folded DNA in the nucleus way back in the 1980s, but this does provide better methods of imaging it. The second point is that one of the agents of this structure is long non-coding RNA — that is, RNA that isn’t translated into protein, but functions to link DNA and proteins into loops of associated active regions. This RNA works like little bungee cords to tie related elements together.
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So here’s their model. non-coding RNA (ncRNA) aggregates around RNA polymerase as it works, and forms a mass that can bind to other regions of DNA and to proteins, binding them together into a compartment that promotes further synthesis of mRNA.
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This isn’t a surprising idea to biologists. We’ve known for a long, long time that DNA is organized in the nucleus, for example: there are structures called nuclear pore complexes, where arrays of proteins in the nucleus bind to newly synthesized RNA and expedite its export directly to pores in the nuclear membrane, and then to the cytoplasm for translation.

But, I ask you, what does this have to do with the proportion of junk DNA in the genome? It doesn’t. Whatever hack wrote the Discovery Institute article didn’t understand the paper. I think they saw nothing but that it was about a novel function for non-coding RNA, and they leapt to the conclusion that this was about junk DNA. “Non-coding” is not a synonym for “junk DNA”, although creationists think so.
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So let’s take a look at a comprehensive review of non-coding RNA. This is an excellent review article by Palazzo and Lee that I recommend highly if you want to figure out what the real story is about ncRNA.
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Starting with the discovery of transfer RNA and ribosomal RNA in the 1950s, non-coding RNAs (ncRNAs) with biological roles have been known for close to 60 years. Even in the late 1970s and early 1980s the existence of other functional ncRNAs was known, including RNAse P, snRNAs, and 7SL [the RNA component of the signal recognition particle].

Note that the Discovery Institute wants to claim that the idea of functional non-coding RNAs was derived from Intelligent Design thinking, but actually, it has been common knowledge in the biology — that is, the real biology — community for decades. It’s so old that it’s what I learned as an undergraduate, which was ages ago.

Palazzo and Lee go on to point out that this notion of pervasive transcription has also been around for a long time, and that there are a few people, like John Mattick, who still promote this idea that every bit of the genome is transcribed and therefore functional, which is absurd.

This idea was epitomized by the ENCODE consortium, which claimed to have assigned “biochemical functions for 80% of the genome”. Others have disagreed, pointing out that the vast majority of these novel transcripts are present at low levels, and that the term “function” had been misappropriated.

Yeah, that’s what I think. It’s pretty hard to argue that RNA polymerase is flawless and perfect and never errs in RNA transcripts. Palazzo and Lee again:
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It is important to recognize that the pervasive transcription associated with the human genome is entirely consistent with our understanding of biochemistry. Although RNA polymerases prefer to start transcription at promoter regions, they do have a low probability of initiating transcription on any accessible DNA. Indeed it has been observed that most nucleosome-free DNA is transcribed in vivo and that many random pieces of DNA can promote transcription by recruiting transcription factors

But let’s focus on the implied claims of the Discovery Institute. Is this discovery by Quinodoz and others of a role for some ncRNAs represent a revelation that shows the human genome is mostly, or even entirely functional? I don’t think so. Here’s the key point from Palazzo and Lee — long non-coding RNAs are only a tiny fraction of the genome, so identifying a few lncRNAs that have a function cannot tell you that the whole genome is functional.
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As of spring 2014, the LNCipedia website has compiled a list of ∼21,000 human lncRNAs, with an average length of about 1 kb. These would originate from <1% of the human genome. Needless to say, this is a very small fraction of the total. Even if we compiled all of the putative lncRNAs using the most optimistic analysis, all the putative lncRNAs would still be transcribed from at most 2% of the genome.

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They go on, in brief:

In summary, our best candidates for novel functional ncRNAs (lncRNAs, eRNAs) arise from only a minute fraction of the genome. Again it appears that the vast majority of the genome that falls outside of these loci is transcribed into junk RNA that is present at very low levels at steady state.

lncRNAs are less than 1% of the genome. Even if every single one of them was demonstrated to be performing an essential function, they are a small drop in the bucket of the entire genome. And that functionality has not been demonstrated, except in a few examples.
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Thus far, only a small minority of lncRNAs have been shown to be important for organismal development, cell physiology, and/or homeostasis. As of December 2014, the LncRNA Database, a repository of lncRNAs “curated from evidence supported by the literature,” lists only 166 biologically validated lncRNAs in humans. Additionally there are so called eRNAs, which according to FANTOM5 come from an additional 43,000 loci. However, at an average length of ∼250 nucleotides they would be made from ∼0.34% of the human genome. Again, these are very small numbers.

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So the Discovery Institute article concludes by saying:

This is a paper to remember. It shows in hindsight the fruitfulness of the ID perspective over the evolutionary one. Evolutionary thinking dismissed these non-coding RNAs as junk. ID thinking would have approached the unknown with the premise, “If something works, it’s not happening by accident.”

The second and third sentences are outright lies. The Quinodoz paper was not inspired by Intelligent Design creationism — it builds on prior work on molecular and evolutionary biology that emerged out of the 1950s. Evolutionary biology does NOT dismiss non-coding RNAs as junk. Evolutionary thinking approaches these scraps of RNA with the premise that function can’t be assumed, it must be demonstrated.

That’s it. That’s all I’ve got to say. The Discovery Institute mangled and misinterpreted an article in a science journal to twist it to support their silly agenda. News at 11.

DI — Caltech Finds Amazing Role for Noncoding DNA

Caltech Finds Amazing Role for Noncoding DNA

Quinodoz and others — RNA promotes the formation of spatial compartments in the nucleus
https://pubmed.ncbi.nlm.nih.gov/34739832/

Palazzo & Lee — Non-coding RNA: what is functional and what is junk?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4306305/

Comments

  1. nomdeplume says

    Oh PZ, I find my knowledge of genetics, gained nearly 60 years ago (the discovery of the double helix was still news…) inadequate to cope with all this complexity…

    Occurred to me recently though that “Intelligent design”, quite apart from having no mechanism, and no evidence, is disproved quite simply by the great variation in morphology of most vertebrate species including humans, a range of variation that includes dysfunction. Surely a designer would be using a blueprint with no variation?

  2. bcw bcw says

    OK, I think we need a shout-out about the cool font dingbat/ornament spider markers used as paragraph separators in the above PZ post. I think they are new unless I’ve just missed them before but in any case they are truly fine.

  3. birgerjohansson says

    I just visited Youtube and went through PZs debunking.
    Kudos for setting aside time for reading a creationist tract and listing all the ways it missed the point.
    It must be as painful as listening to Boris Johnson and trying to follow his train of thought.

  4. Rich Woods says

    @birgerjohansson #5:

    It’s easy to follow Boris Johnson’s train of thought: “If I don’t benefit from this right now then I’ll just lie about it. Any old lie will do — tomorrow is another day.” The rest is just noises he makes.

  5. PaulBC says

    ENCODE, readers recall, found that 80 percent of the genome is transcribed, even if only a small part codes for proteins.

    Isn’t this a concession that at least 20% of the genome has no conceivable function? While I agree that that’s true of a much higher percentage, I think they should least get to work explaining the part that isn’t even transcribed before declaring victory. How would 20% junk make a case for “it’s not happening by accident.”

  6. says

    No — Ewan Birney suggested 80% was a lower bound, and it could rise to 100%.

    The spider dingbats were my cue to move on to the next image. I am really barely functioning right now. I have one more class to teach tomorrow, and I’m dreading it.

  7. PaulBC says

    Brony, Social Justice Cenobite@9 I don’t think that’s what ID people mean though. I found this article persuasive and I think I’ve read it before: The case for junk DNA. I was searching just now and it came up. I was initially thinking about the fact that if a region is not conserved, it’s a safe bet that its sequence doesn’t matter that much. But (unless I’m misreading you) you would call that “taking mutagenic hits for functional regions.” Note: I don’t see how you “take hits”–the probability of mutations in encoding regions is independent of non-coding regions as far as I know–but I don’t want to digress on that.

    Here’s an analogy: pillow stuffing has a function, but the exact configuration of any clump of pillow stuffing is not relevant to its function provided it has the appropriate bulk characteristics. It may be that it’s good to have a big mass of DNA in addition to the part that encodes proteins or has other functions when transcribed. But if its sequence doesn’t matter, then at least at that level it serves no functional purpose. As the linked article points out and PZ also stated, biologists have known for decades that some non-coding DNA (i.e. that does not encode a protein sequence) has a function. That’s not a surprise at all. There still seems to be a very small percentage for which the sequence really matters, as evidenced not only by the fact that the “junk” is not conserved but the fact that much of it is repetitive. This seems to be the part under contention that ID people are just certain has a “function” and not just to add bulk.

    Another great point that seems a lot simpler than any of the above is the “onion test”. In short, why should an onion have so much more DNA than a human? Or in general, why is DNA size so variable and apparently uncorrelated with our notion of the complexity of what it encodes (admittedly a difficult thing to nail down)?

    So when you refer to “a physical substrate for the cell’s metabolism” I would ask, do you really need that much substrate? Is its sequence significant at all? If the answer to these questions is “no” then there is no “complex specified information” (or whatever ID people are looking for) and this is not what they mean when they insist it’s not “junk.”

    My impression (again backed by the paper) is that biologists understand the fraught nature of the term “junk”, which had a specific meaning when introduced by Ohno, but their view has hardly budged for the most part that very little of the gene sequence actually has any effect on the resulting organism, a point that that can be summarized in the monosyllable “junk.”

  8. says

    @PaulBC 10
    I was naming more functions. Not paying particular attention to ones they might necessarily pick. I did skim a bit.

    More specific responses later but DNA is the physical substrate for the cell’s metabolism, I mean in the sense that it is a physical platform for making ribosomes to cell membranes, and the gene transcription that makes the proteins that more directly does the metabolism.

  9. says

    @PaulBC 10
    After thinking a bit more my listing had to do with the fact that both ID and ENCODE were on the page as examples of, poorly restrained pattern detection maybe?

    DNA:
    1: contains the sequences that determine amino acid chain alignment. A more chemically stable source relative to RNA with respect to alkaline conditions and self-splicing.
    2: provides a physical location for amino acid chains to bind through charge attractions

    2 is a concentrating mechanism for the results of 1 as much as membranes are.

  10. PaulBC says

    Brony, Social Justice Cenobite@13 Well, I think I understood roughly your point, but I don’t believe it’s what IDers and creationists mean when they doubt the existence of junk DNA. The sequence of coding regions clearly matters, as well as other regions that have been shown to control gene expression. Everyone agrees that this small part of the genome is not “junk DNA”.

    No such functions have been identified for the majority of the DNA present in a genome. As the paper I linked notes:

    Another large fraction of the genome consists of highly repetitive DNA. These regions are extremely variable even amongst individuals of the same population (hence their use as “DNA fingerprints”) and can expand or contract through processes such as unequal crossing over or replication slippage.

    There may be some reason it’s useful to have regions like this around. I have no idea. But the above seems to establish that the precise sequence of these regions just doesn’t matter at all.

    Maybe a better analogy that pillow stuffing would be old newspapers. These have many uses that have nothing to do with the content. “Fish wrap” for one. Or they can be shredded and used for packing material.

    If I received a delicate vase in the mail and found it was shipped with old shredded copies of the New York Times, then that paper had a function of preserving the vase. However, the function was entirely independent of its informational content. I think that if one were to tell an IDer that some amount of DNA is metaphorically there as packing material and that’s why it can be called “junk” (whether accurate or not) I doubt they’d insist that this is the reason it’s not junk. Instead, they’d claim that the sequence is part of the “design” and must have meaning (as PZ states, it’s unclear why they think this is important, and can’t just acknowledge it as divine doodling).

    Extending the metaphor, it seems like they are the ones who would look at packing material and insist that there was some deep significance to the David Brooks columns, socialite wedding announcements, and lingerie ads or whatever, and if you continued to receive identical vases with shredded newspaper, all different issues, they would never grasp why you feel comfortable calling it junk.

    That aside, the variation in genome size also suggests that different organisms get by with different amounts of bulk DNA. This does not mean you could refine every genome down to the bare minimum, but it does suggests you can get away with removing a lot. Hence “junk.” It seems like a totally appropriate term to me.

  11. chrislawson says

    PaulBC@14–

    There is a whole subdiscipline of evolutionary theory where researchers knock out as much of a genome as possible while still producing viable organisms. As part of the same project, researchers (often the very same teams) are also trying to build organisms from the ground up using the smallest possibe genome.

    Much of the research has been done on mycoplasma because it has a the smallest genome (M. genitalum has only 475 genes, of which we know from knock-out studies only 381 are essential) of any organism that can be grown in pure culture — but one of the reasons mycoplasmas can survive with such a small genome is that they are obligate intracellular organisms, that is, they can only live inside other cells that are doing a lot of the metabolic work for them (or in a laboratory culture medium that simulates the intracellular environment).

    https://en.wikipedia.org/wiki/Mycoplasma_laboratorium

    The smallest known genome of an independently-living organism is Ca. Pelagium communis with 1389 genes. This extremely pared-down creature is possibly the most common organism on the planet. It is estimated to make up to 25% of all microbial plankton. And yet it was first isolated in 2002. There’s still a lot to learn about biology! And it also shoves a great big dagger in the heart of the “complexity = success” argument.

  12. says

    @@PaulBC 14
    I agree that my examples don’t work so well with ID.

    I wish the paper included a table of the different kinds of repetitive sequence. I may have to hunt for the contents of their #30.

    Stress as mutagenic trigger for adaptive diversity is an idea I’ve seen.
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3697269/
    “In contrast to point mutation mechanisms in which polymerase errors are responsible for an increased mutation rate, adaptive amplification is hypothesized to occur via a transcription-coupled, microhomology-mediated, break-induced replication mechanism [Hastings et al., 2009a]. In humans, it is also hypothesized to underlie copy-number variation in humans [Hastings et al., 2009b]. Adaptive amplification is restricted temporally to times of stress, and through coupling mutation to transcription, amplification is also restricted spatially to those regions of the genome experiencing high transcriptional activity; the very regions that have the best potential for yielding an adaptive advantage. The ability to restrict mutations not only temporally but also spatially within the genome is critical for minimizing the accumulation of deleterious mutation, and is not unique to bacteria as multiple organisms have specific genomic regions that are more mutable and therefore classified as mutational hotspots (fig. ​(fig.1c1c).”

  13. unclefrogy says

    I am amazed at the depth of detail we have gotten to with the biochemical and DNA research and I know we have much to learn yet
    I suspect that in their heart of hearts the people who believe in creation science do not really understand things at that level of chemistry but really just believe in the magic of god and his creation. their approach to the question is a legalistic approach based on the kinds of arguments offered in a court of law, not the kind of ‘arguments” that takes place within science which are based on trying to figure out what a thing is how does it do what it does how did it get here and what is here anyway the truths of existence

  14. says

    But what do you do when you get down to what came before DNA? My imagination is playing with the idea of something that acts as an un-zippable conveyer belt of things that connect with the first half of the purine pathway. Once the first ring forms that Ribose linked 5-membered ring with an extra -NH3 also goes on to make part of Thiamine (moves C2 groups around in Ribose biosynthesis, and other C groups), and a “lower ligand” of B12
    https://en.wikipedia.org/wiki/5-Aminoimidazole_ribotide
    https://www.researchgate.net/figure/Biosynthetic-pathways-of-purines-thiamine-and-tryptophan-shown-schematically-with-the_fig2_40446576
    https://www.pnas.org/content/112/34/10792

  15. chrislawson says

    Creationists/IDists are trying to pull a god-of-the-gaps argument in that they keep postulating that our genome is 100% functional but we just haven’t found the explanation for every function yet. The probem is that junk DNA is not just “DNA we don’t know the function of.” There are definitively known regions of DNA that have no function. For instance, humans only get scurvy because the vitamin C gene is broken in primates. We still have the gene. But it doesn’t make a functional protein. Nor does it serve any other function. There are many such “pseudogenes” in the human genome.

    Worse than the pseudogenes are the transposons — almost half of the DNA in the human genome is made up of self-replicating sections of code that reinsert copies of themselves into other parts of the genome. Not only does this serve no function to the organism, it creates a metabolic burden to reproduction, and sometimes the transposons copy themselves into coding sections and disrupt the genes. Haemophilia A and B, Duchenne’s muscular dystrophy, porphyria and other genetic diseases are caused by transposon disruption of important genes. Transposons can also cause chromosomal misalignment during replication.

    (Note, a small number of cases have been identified where transposons might play an adaptive role in some organisms. No doubt the IDists will say this proves that all transposons have hidden functions while completely ignoring the much, much larger number of known explicitly maladaptive transposons — of which even a single example would blow their argument away if they were honest investigators. These possibly adaptive transposons are almost certainly from organisms evolving to recognise certain transposons as transcription sites rather than from transposons being inherently 100% adaptive.)

  16. chrislawson says

    Brony@18–

    I think there is so little solid evidence that we are a long, long way from understanding the origins of life or the early evolutionary pathways. Still, nothing wrong with conjecture, so conject away! The only thing that I think is almost a certainty is that life did not start as an early cell from which all earthly organisms then branched, but from a complex intermingling of nearly-cells and quasi-metabolic chemistry, of which such a small subset survived that it almost looks in retrospect like evolution from a single common cellular ancestor. This is, of course, not a new idea. It’s pretty much what Oparin and Haldane were suggesting way back in the 1920s.

  17. says

    @chrislawson 20
    I think metabolism is evidence. We just have to put the parts together in an informative way. I’m drawing metabolism centered on PRPP, the form of ribose used to make purines (A G), pyrimidines (U/T C), NAD (proton dispenser/extractor), and the genetic code associated amino acids Tryptophan and Histidine.

    Purines and pyrimidines are synthesized in reverse fashion. The purine rings are built onto ribose (NH3+glycine+formate+NH3)>
    AIR (Thiamin/B12 branch point) > (bicarbonate+NH3 (+genetic code associated Aspatrate – TCA asscciated fumeratr)+formate) > IMP
    Then Aspartate is bound and fumerate leaves again in an another “indirect amination” (the same process is part of making genetic code associated amino acid Arginine). To get GMP NAD is involved in O addition, and then NH3 is added to another part of the ring.
    The pyrimidines are made from bicarbonate+genetic code associated aspartate that is made circular, and loses H2 before binding to ribose to make OMP (similarly rings are made and added for NAD and tryptophan, histidine starts with ATP and PRPP).

    To all of that I added the rest of Thiamine biosynthesis and have just about finished adding the protein domain superfamily associations for the whole thing using Uniprot and ECOD.
    https://www.uniprot.org/
    http://prodata.swmed.edu/ecod/

    Next I start rearranging and looking for patterns among the protein domain superfamilies. It’s like a rubik’s cube/matryoshka doll/”where’s waldo” combo.

    he pyrimidine ring

  18. says

    And I need to sort and include stuff like the membrane component assembly/adaptor function of U and C. And the thematic differences between ATP/GTP/CTP… as phosphate “energy currency”. GTP does translation, and motor proteins…
    And ATP acts like an adaptor for NAD and other cofactor like coenzyme-A, and FAD (riboflavin+AMP)…
    But GTP is physically deconstructed and made into folate like ATP and PRPP get turned into Histidine. Folate is a formate donor for purine biosynthesis, in some organisms. Other use formyl phosphate.

  19. raven says

    The creationists lies fail on any level you care to look at them.

    Some of the evidence against their no junk DNA lies is looking at other genomes. Genomes can differ by a lot in size even among closely related organisms. Plants are known for having far larger genomes than humans, to take one common example.

    Plant Genome Size
    Plant nuclear genomes have a huge range in size, from some 125 Mb of DNA in a range of species including crucifers, roses, some trees, pteridophytes, and bryophytes, up to more than 70000 Mb found in other pteridophytes and angiosperms (one lily has a genome of more than 120000 Mb).

    Genome Size – an overview | ScienceDirect Topics https://www.sciencedirect.com › topics › genome-size
    Search for: Plant Genome Size

    Plant genomes range in size from 125 megabases to 120,000 megabases. For comparison, humans are 3,000 megabases.

    So why does an onion need 16,000 megabases, 5 times a human’s 3,000 megabases.
    Why does an onion need 16,000 megabases while another closely related monocot needs 120,000 megabases.
    The answer is they don’t. Noncoding DNA is not constrained by evolution very much and can and has increased and decreased during the history of various lineages.

  20. raven says

    The genome sizes of mammals have a range similar to that of non-avian reptiles, from a minimum of 1.7 to a maximum of 8.4 pg/N and an average of 3.5 pg/N, close to the value for man.Mar 12, 2016

    Transposons, Genome Size, and Evolutionary Insights in …

    To take an example closer to humans, the closely related mammals have genomes that differ by a factor of 5 in size.

    We even know why this is to some extent.
    8% of the human genome is defective retroviruses, the wreckage of ancient invasions of our genome.
    45% of the human genome and 37.5% of the mouse genome are transposable elements.
    A few of those at .05% are still active.
    The vast majority of expandable and expanded genomic DNA has no known function.

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