Origins of Life – Amino Acids and the Triplet Codon

ResearchBlogging.orgOne question that always seems to come from the anti-science crowd when discussing the origin of life is, “Where did the genetic code come from?”.

Scientists will often point out the simple fact that every living thing on the planet (so far discovered) uses the exact same codons to translate DNA into proteins.  The same amino acids are used, the same coding system is used (CUC is always leucine, no matter if one is looking at archaebacteria or a blue whale).  This is taken to be evidence of common descent.  It makes sense, if everything uses the exact same system, then they must be related somehow (considering that there are no ‘decisions’ made by organisms without a mind to make decisions.)

Of course, the anti-science supporters will often say, “Of course, it’s the same, it was designed that way.”  Which gets us into the whole teleology that is modern creationism. But that’s not why we’re here. 

The question remains, how did this system develop?

 Edward Trifonov may have answered this.  Remember, this may not be The Answer, but it shows that the system is plausible without outside interference.  This is all science has to show.

Previous articles here have shown that amino acids do indeed form from non-organic starting materials.  The classic Miller-Urey experiment showed this almost 60 years ago.  But, there was something hidden in the Miller-Urey data.  Something no one even really thought about until Trifonov took a look at all the data.

He and Thomas Bettecken wondered if the GCT triplet, which extends itself rapidly in disease, has/had an evolutionary advantage.  If so, then this system (GCU) could have been the first codon.

Point mutations are simple one nucleotide replacements in the genetic sequence.  (How’s that for a poor segue?)

What they found was that six of the amino acids in the Miller-Urey experiment were encoded by point mutation derivatives of GCU.  We know these are easy to form, just about anyone with access to some glassware and pure gases can make these amino acids in a way similar to what may have happened on the prebiotic Earth. 

It’s surprising, though it shouldn’t be, that the evolutionaryily powerful GCT triplets are closely associated with the earliest and easiest to make amino acids.

Well, that’s interesting, but where do we go from here?

Trifonov decided to go all the way, all 20 amino acids were individually characterized with 40 criteria.  He used everything from how many non-hydrogen atoms where in the molecule to the thermostability of the duplex RNA genes.  Now we get to the interesting bit.

 What he found was that using all the criteria, 9 of the Miller-Urey amino acids, would have been the first 9 in a chronological sequence.  Then he took the Miller-Urey data out and checked again.  The same first 9 appeared (though one moved from position 6 to position 5).  Then he filtered the data for only certain things, like closely related, but different criteria.  Almost no matter what he did to the data, the rankings of the amino acids came out the same.

 Oh a couple of amino acids moved up or down one spot, but the correlation between all data sets combined, and groups of data, and experimental evidence was very, very high.

 What’s even more interesting is that he looked at the RNA codons for each amino acid.  Now that he had a temporal sequence of amino acids, he could actually look at the temporal sequence of the codons.

 He found that, starting from GGC (which for other reasons is considered one of the earliest codons), every codon followed a simple step-wise path of point mutations or complimentary sequences.

 Let’s go through an example, and please bear with me:

  • GCC alanine
  • GAC aspartate
  • GAG glutamate
  • CUC leucine (this is the compliment to GAG)
  • CUG leucine
  • CAG glutamine

Using these steps, every amino acid / codon combination (all 64 of them) can be developed through either point mutations or complimentary sequences.

The main factor he found, was thermostability we very important.  The most thermostable of a codon was the first one developed.  Even though a future codon might have been more stable than earlier codons, if there was no step-wise or complimentary path to the more stable one, it did not emerge until such a path was available.

 There are four fundamental conclusions developed by this work.

  1. The first amino acids were abiotic.
  2. Thermostability played a major role in the development of the triplet code
  3. New codons appeared in complimentary pairs
  4. New codons were simple derivatives of chronologically earlier ones.

 So, unlike what many believe, even scientists, then entire codon/anti-codon/amino acid system did not appear, fully complete.  It, just like everything else, evolved.

____________________________________________

Trifonov, E. (2000). Consensus temporal order of amino acids and evolution of the triplet code Gene, 261 (1), 139-151 DOI: 10.1016/S0378-1119(00)00476-5

About these ads
This entry was posted in Biology, Evolution, Origins of Life, Research Blogging, Science and tagged , , . Bookmark the permalink.

7 Responses to Origins of Life – Amino Acids and the Triplet Codon

  1. Roy Sites says:

    Life from non-life is so simple, wave a hand here and another there and you have life. Let’s assume, for the moment, that you are correct; then why do we not see new life forms coming into existence now? These protiens and amino acids should be even more prevelent now than 4 billion years ago. Scientists should be able to bring this soup to life in the lab. Oh, let me see they cannot, how strange and just maybe it is not all that simplistic after all. Keep waving your arms, who knows, something besides smeely air might just happen — NOT.

  2. ogremkv says:

    Roy, there are two very good reasons we don’t see new life coming into existence now.

    1) Oxygen. The oxygen that is critical for most modern life and all advanced life is highly detrimental to the chemical reactions needed to form the basic building blocks of life. Abiogenesis, as described in this and other articles, requires a reducing atmosphere.

    2) There’s already life here. Any abiotic organic compounds are quickly absorbed by currently living things as fuel and nutrients.

    As to why scientists have not created life… please point me to the experiment where they tried and failed to do so. Oh wait, there isn’t one. Scientists aren’t trying to ‘create new life’. There’s no real point.

    However (and I said this in EVERY post I’ve made on the subject), if it can be shown that all the steps are chemically and physically possible, then we don’t have to actually do the work. I know how to build an atomic bomb, I don’t actually have to build one to prove that.

    Finally, what other prospect is there for abiogenesis? Please describe a testable hypothesis that posits and explains another way for life to get here. Please describe the experiments that you would use to show this is valid. Please… I’ve been asking for this for years… and no one has ever done so.

  3. derwood says:

    I have to laugh when I see comments like Roy’s. One can safely assume that he is either a YEC or an ID proponant (2 sides of the same coin as far as I can tell) – yet there he is, wondering why we do not see life popping up anew all the time.
    Why do we not see overt acts of Divine Creation occurring all the time? Did Yahweh/the ‘designer’ run out of gas?

    There he is, telling scientists t0 keep waving their arms, and maybe something will happen.
    Keep waving your arms, Roy, maybe someday Jesus really will return, and maybe the ‘designer’ will be with him.

  4. Swan says:

    You said: “The same amino acids are used, the same coding system is used (CUC is always leucine, no matter if one is looking at archaebacteria or a blue whale). ”

    First, let me say that I’m no expert in biology. so I’m probably missing something basic. I have been reading recently about the endosymbiotic theory concerning the origin of motochondria. The book I’m reading was published in the mid 80s, so I’m pretty sure much more work has been done to advance this theory, and many significant facts have been uncovered since then.

    In that book, the author mentioned that one point of evidence in favor of the idea that mitochondria used to be an independent organism (a really, really long time ago) was that it didn’t use the same codon sequences to code for specific amino acids. The author made a point of how the non-universality of the DNA code was very surprising to biologists. The implication was that it was undergoing its own line of evolution since the time of the merge.

    Can you comment on this? Is it in fact true that mitochondria DNA has a different “code”? Has this been disproved?

  5. OgreMkV says:

    Yes, it is true that mitochondria do use a different coding system.
    I haven’t studied it much either, so I’m in the same boat you are. I would not that mitochondria seem to be doing their own thing and that this provides additional evidence for the endosymbiotic theory and common descent.

    Basically, the mitochondria are all different in the same way (mostly). UGA in all mitochondria (from fungi to animals) is tryptophan and not a stop codon as it is in the organisms that the mitochondria inhabit.

    Thanks for the information. More studying to do.

    Isn’t it amazing how some people can accept changes to their knowledge?

  6. RossN says:

    The anti-science crowd likes to imagine that life evolved.
    The pro-science crowd, on the other hand, notice that there is an array of impossible odds to overcome in a naturalistic beginning to life.

    Just one example: Abiogenesis requires a reducing atmosphere, however oxidized minerals such as hematite are found as early as 3.8 billion years old, almost as old as the earliest rocks, and 300 million years older than the earliest life. Many more cited here http://is.gd/EmckmR

  7. IDNeon says:

    I noticed a logic error where someone said the reason amino acid soups dont turn into life are because 1) oxygen destroys it and 2) life eats it up. The logic error is that 1 and 2 are mutually exclusive. So which reason does amino acids not spontaneously create life?

    Furthermore the other part to which the illogical moron failed to answer is why cant “scientists” reproduce such obviously inevitability in a laboratory under the most ideal conditions?

    Evolutionists must be the dumbest and most blinded religous people on Earth. Worse than Muslism.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s