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[Music]

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[Applause]

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hi everyone my name is Tyler Roche I'm a

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grad student in the HUD lab at Georgia

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Tech and I'm working with the Center for

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chemical evolution so I'm just gonna

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thank you all for coming to my talk

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I'll be discussing the prebiotic

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relevance of keto sugars to the origin

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of Aldo's nucleotides so the RNA world

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model is a problem

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a popular hypothesis for the formation

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of the first genetic polymer RNA as

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posed by the model at the CCE we think

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that there could have been perhaps a

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proto RNA or some sort of genetic

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polymer that preceded RNA in the

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chemical evolution of of genetic

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polymers so you can imagine that in the

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same way that you could have a

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modification from RNA to DNA by the

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removal of the hydroxyl group on the 2

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carbon and the replacement of thymine

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for uracil you could have had some other

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substitutions from a proto RNA system

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including substitutions of perhaps the

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ionized linker which in RNA is a

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phosphate the tri functional connector

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which in RNA is ribose and the

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recognition unit components which in RNA

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are the canonical nucleobases that we

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know so with this model in mind it would

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be interesting to understand how these

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components were formed and combined to

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form either the proto RNA or the RNA

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itself as chemical evolution proceeded

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so in terms of RNA synthesis in a

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prebiotic context there are several

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stages that had to be undertaken for the

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RNA to form into it's fully oligomers

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state so we can imagine that the several

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steps included sugar formation nucleus

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sedation are glycosylated

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phosphorylation or oligomerization and

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all of these staff pose various

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challenges to prebiotic chemists

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attempting to understand how these

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happened so today I'm going to focus on

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sugar formation and nuclear sedation as

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two of the steps that I'm interested in

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looking at and investigating so the

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foremost reaction is the reaction that's

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most frequently invoked to explain the

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formation of sugar

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on the prebiotic earth and in fact the

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foremost reaction can form a variety of

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different sugars you can have branched

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sugars unbranched sugars keto sugars

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Aldo's sugars all sorts of different

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sugars with this reaction so if you're

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looking for ribose which is part of RNA

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it's not necessarily gonna be the

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easiest thing to find in fact in this

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chromatogram you can see that it's one

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of the many peaks present and it's not

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particularly large as one of the peaks

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so the question becomes how did life

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select for ribose how did it

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come out of this vast mix of sugars

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another question regarding the formation

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of RNA includes nucleus addition so

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there have been experiments showing that

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canonical nucleobases don't readily form

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nucleosides when combined with RNA and

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or combined with ribose in water you can

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form some nucleotides with some of these

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but it's not an easy process it's not

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something that happens in very high

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yields however research in the Center

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for chemical evolution has looked at

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various non canonical nuclear bases that

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have various properties that are

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beneficial potentially to their

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prebiotic formation into these

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nucleotides including their reactivity

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and their ability to undergo super

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molecular assembly so when you react

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these nucleobases with ribose you do in

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fact form nucleotides that can perhaps

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be selected for into a proto RNA system

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so in the non-canonical nucleobases

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react more readily to form these

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nucleotides so research performed by one

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of my group members David feel hoe

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included reactions with sugars and try

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me no prima diene to see if you could

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form nucleus IDEs with all these

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different sugars and the triggers of

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interest obviously for me include ribose

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and rib ulos so when you react tap with

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these sugars you can form these

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nucleotides fairly readily but an

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interesting result of his was that if

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you react tribulus which is a keto sugar

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with tap try me no prima diene you can

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in fact form nucleotides

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formed as if they're from the aldose of

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that sugar so alder nucleotides but not

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kitto nucleotides were detected as

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products so to kind of get into that

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talking about aldoses and ketoses what

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do I mean exactly so when you look at

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these two sugars ribulose and ribose

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they're isomers they're both 5 carbon

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sugars rib ulos is a ketose because it

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has a ketone functional group and ribose

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is an aldehyde or an aldose sugar

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because it didn't it has an aldehyde

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functional group and in fact these can

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interconvert this is the mechanism by

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which it is thought that there

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interconverting and it involves the

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formation of an enol and then the

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migration of a carbonyl group so you can

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have this inter conversion between these

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ribose and rivulet sugars or any other

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elders and keto sugars and in fact you

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could have the same sort of thing

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happening with arabinose which is just

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another isomer of ribose that differs

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based on the chirality of one of the

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carbons so my hypothesis when looking at

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these sugars is that perhaps the

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nucleobases in solution could attack and

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trap the aldo sugars but not the keto

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sugars in the form of nucleotides and

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this is perhaps how the nucleotides were

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able to be formed on the early Earth so

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for one of my first experiments I wanted

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to see if I can look at the

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isomerization of rebel OHS which is a

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five carbon sugar that could isomerize

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into ribose and arabinose and I

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basically incubated this rib ulos at 65

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degrees for three days and looked at it

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by NMR and so the first spectrum you see

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appear is just the time point zero which

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should just be Regulus in solution and

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in fact you see the standard spectrum

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for rib ulos and when you allow that

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Regulus to incubate over time for three

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days you took a look at it by NMR and I

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can identify Peaks that were

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correspondent to both ribose and

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arabinose now there are hypothetically

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more than these possible Peaks that

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could form in terms of all the possible

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different four configurations of ribose

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and arabinose including the furanose

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pyranose forms the alpha beta and

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so some of those Peaks are present some

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of those are not present in high enough

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concentrations because there is a

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dynamic equilibrium between those that

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prefers a certain configuration for

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those sugars so the result of this is

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that right rib ulos does readily

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isomerize in solution into ribose and

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arabinose the next experiment that I

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performed was one where I'd ride down

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review lows with try Meena prema Dean

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and I wanted to see if I could form

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different nucleotides both arabinose and

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ribonucleotides

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and so I performed this reaction these

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are the possible linkages that could

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form with these nucleotides and I've

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omitted the pyranose forms but those

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could possibly exist as well and after I

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perform this reaction I looked at it via

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NMR and I was able to identify Peaks it

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not only correspondent to the isomerized

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sugars ribose and arabinose here more

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about another arabinose peak here but i

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was also able to identify Peaks that

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corresponded to nucleus sides of tap and

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these sugars so the results here is that

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it's pretty clear that RHIB ulos does

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form these aldo nucleotides when it's

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reacted with triming up remedy so

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another experiment that i performed then

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was basically i wanted to take each of

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these sugars and incubate them over time

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to see if I could get sort of a

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long-term ink isomerization rate one

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sighing queue baited them I would take

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time points every day and then I would

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react those time points with barbra

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Charak acid at room temperature now

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barbarick acid was useful in this

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experiment for two reasons one it is

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quite visible via UV so it allowed us to

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monitor the progress of these reactions

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or the amount of nucleoside formed when

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we analyzed it by lc-ms and the other

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benefit of using barbra toric acid is

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highly reactive so it's one of the most

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reactive nucleobases that we work with

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and so I could perform this reaction at

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room temperature which means once it's

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heating up and inked and isomerizing at

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a higher temperature if I bring it down

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to room temperature presumably it sort

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of freezes the isomerization state of

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those sugars you know locks in the

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different concentrations of

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arabinose or rib Boulos and then it will

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react with the barber trick acid form

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those nucleosides and then I can track

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them so the results of this experiment

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showed that these the screen trace is

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ribose this blue traces arabinose just

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reacted with barbarac acid after being

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allowed to incubate for just a day and

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then the two red traces are Regulus

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the first one is regulars incubated for

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one day and then the darker red trace is

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RHIB ulos incubated for 408 hours and

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these are all at 65 degrees and once I

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react each of those time points with

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barbaric acid you can see them here now

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I have scaled these up the yield of the

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nucleotide formation is small so I've

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scaled up so that you can see the

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formation of these Peaks and what you

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can see is that the formation of the Rye

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beside Peaks are increasing as you allow

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Regulus to isomerize over time and you

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can kind of also see the formation of

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this small arabinose I'd peak as well so

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the result of this is that once you

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allow RHIB ulos to isomerize in solution

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it can go to either ribose or arabinose

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which then once I add barbaric acid will

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react to form these nucleotides I did

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the same experiment with hexa sugars

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just to see if these trends followed

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based on the fact that there are ketosis

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and didn't have any effect based on the

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carbon number and you can see the same

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thing here so the green is glucose at

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not incubated at all reacted with

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barbour Turek acid the blue trace is

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mannose again not incubated for any time

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reacted with barbaric acid so you can

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see that there's a large peak here that

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represents a glucoside or a glucose

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nucleoside and there's a large peak here

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that represents a man aside or Manas

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nucleoside and when I incubate fructose

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for 408 hours you can see it go from

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having no nucleoside peaks to having

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large mannose and glucoside peaks so

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this again to me indicates that when you

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have these keto sugars and you let them

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incubate over time the

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interconvert into the different aldose

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isomers and those can then react with

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nucleosides or with nucleobases to form

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nucleotides so the scheme that I'd like

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to leave you with is one where you have

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something like rib ulos for example

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which not only can interconvert between

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sugars but you know these sugars go

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between their linear and cyclic forms so

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you could have regulars that can

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interconvert to ribose and arabinose as

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well and these can again also

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interconvert with their cyclic forms but

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not only do you have this system which

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i've kind of demonstrated you could

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hypothetically have a larger system

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where you could have regulars

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interconverting in twos i lullo's by the

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carbonyl or the formation of an enol in

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between the 2 and 3 carbons rather than

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the 1 and 2 carbons and then that could

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isomerize into the sugars look so some

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xylose so in terms of the prebiotic

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context and and implications of this I

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think that once you form these sugars

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you they can isomerize readily and they

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can basically inter convert into any

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possible sugar of that structural

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arrangement and length so once you have

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an unbranched five carbon sugar in

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solution hypothetically could isomerize

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into any other unbranched five carbon

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sugar so in terms of what this means for

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prebiotic chemistry i think that these

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sugar forming reactions don't

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necessarily need to be selective for

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something like ribose if you can form

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rib you Lowe's or any other five carbon

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sugar then you're pretty much there

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you're able to get any other five carbon

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sugar in solution so in conclusion I

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think the prebiotic formation of sugars

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likely allowed for some inter conversion

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that gets you all these different

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isomers you can have these nucleobases

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in the solution that would be able to

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sort of trap these sugars in their

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aldose forms allowing for the formation

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of nucleotides and that life or chemical

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evolution could have selected from this

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large pool of nucleotides on the early

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earth so I'd like to thank my advisor

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Nick hood and my group members

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especially David fiallo for helping me

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out with this

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several other collaborators including

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dr. Krishnamoorthy

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dr. Miller Sivan dr. Schuster and the

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rest of my graduate committee have been

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a great help with this and I'd like to

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thank the NSF and NASA for funding

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[Applause]

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very nice we'll do we have one question

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yes right here

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so then

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it's not yours irreversible you could

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have nuclear sedation and hydrolysis you

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can imagine this is all done in solution

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phase but you can imagine some sort of

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system where there's also a drying cycle

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which it would allow for that nucleoside

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formation to happen and then the other

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component that could drive that nuclear

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sedation in sort of a directed fashion

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is I mentioned that these nucleobases

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assemble in a super molecular fashion so

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you could imagine that perhaps when they

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react with the sugar they could then be

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drawn into the super molecular assembly

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where the sugars hanging off the end and

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then perhaps you could have some

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oligomerization followed you know if

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once you get a critical mass of sugars