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all right hello everyone

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my name is john levoy i'm a phd student

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at arizona state university

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um i'm also studying for the semester at

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the university of glasgow

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so i'm kind of a dual phd student right

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now

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and i'm looking at universal life

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detection

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as is revealed by small molecule

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mine's going to be a little high level

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and i think if we want to talk about

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universal life detection i think we have

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to start off with what is life

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there is a really obvious definition

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here on earth we see a human if we see

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something like this

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if we even see a virus it's very easy to

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say

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those things are alive like we know when

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we see it

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even when it comes to biosignatures we

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start seeing

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if you see something like highway

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interchange or see something like an

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oxygenated planet with lots of water and

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green things everywhere we know that

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that thing is alive as well

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it's very easy to say this thing's not

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random

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this is somehow alive where it starts

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getting a little weird

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is that we don't know the chemistry we

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don't know what a bio signature would

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look like

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um for ref we're on venus what does a

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life

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what does a living molecule even look

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like if we're on an exoplanet we have no

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idea what kind of chemistry

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is there you have no idea what kind of

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um thermodynamics kind of energetic

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constraints

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kind of energy systems there are we

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really have no idea about any of that

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and the life that i can introduce

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beginning this is very much earth biased

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we don't have a universal definition of

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life yet where we can look at something

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and say

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that thing is alive and that thing's not

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so part of what i'm trying to do here

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is to say here is a system for

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measuring chem here's a measurement of

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chemical systems

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that says something is alive or

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something's not um

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and crucially it's going to be chemical

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agnostic

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it's going to say cool

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i think that no matter what kind of

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chemistry we have

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whether it's on venus whether it's on

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exoplanet whatever

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where we don't know what kind of

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chemistry there is we can still look at

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the

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regardless of energy systems

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we're going to define and detect life

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using

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and the way i'm going to do that this is

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one proposal

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one particular way that i believe has

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some

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potential interest i'll explain a few

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others at the end

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um it's something called the maximal

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common substructure algorithm

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all it does is look at

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two chemical species nothing to do with

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the environments nothing with anything

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besides just the two chemical structures

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it's a graph based algorithm

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and what it does is takes it converts

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molecules to graphs

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it's done computationally behind the

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scenes and it takes the largest

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common substructure that's shared

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between those two

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so here we have two drugs and this

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carbon chain with nitrogen benzene ring

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with oxygen attached

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those that that's just that substructure

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is found between

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both of these two and it's the largest

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substructure that is shared between

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these two compounds

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and nothing to do with the chemistry we

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know we didn't even know where these

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came from

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and that's a good thing we're able to

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say we don't know what is going on here

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but there are shared compounds that

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these have potentially some kind of

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shared

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something like that

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and so what i'm doing to kind of say hey

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this is something that we could do

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is i'm starting with earth starting with

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earth kind of getting

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a picture of what life looks like here

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on earth and start comparing it to

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different

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sources um

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because life as we know is my favorite

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earth is only i have n equals one

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way of saying this is what we have for a

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living system

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um so what we do here is take all the

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biochemical compounds from keg

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it's a kyoto encyclopedia of genes and

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genomes

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it's one of the standards for

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small molecule biochemistry

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and we're going to take all these

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molecules whether they're acetyl coa

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some lipids

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some amino acids all this stuff and

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going to take all about 17 000 of those

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compounds and put them all through this

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mcs algorithm so you're going to

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pairwise match every single one

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ends up being a couple billion pairs so

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it takes a while to run

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and you end up with a lot of

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common substructures which return all of

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those

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remove duplicates because there's a ton

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of them and

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then count how many times each fragment

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appears in this data set

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um you're going to end up with a

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distribution pattern of how often

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certain chemical substructures appear

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and we're going to statistically

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distinguish those current patterns

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see if we can say biochemistry is

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different than say an abiotic data set

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um what this could potentially look like

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is

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has some kind of like shared of

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evolutionary

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got a shared chemistry

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throughout and some abiotic

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chemical fragments would be kind of the

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same

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throughout an entire data set so we can

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say life is different than

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whatever this abiotic set is if you see

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something like this we could say

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cool there is some evidence that

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this method could distinguish life from

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non-life living chemical systems from

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non-living chemical systems

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and you kind of see that which is well

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biochemistry looks like kind of what we

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expect um

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there are very few shared compounds

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so a carbon-carbon bond carbon double

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bond benzene ring

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those things appear a lot so they end up

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and they are shared almost throughout

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all of chemistry i think

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something like nearly 100 chemistry has

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a carbon-carbon bond unsurprising

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but there are very few of those shared

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chemical substructures

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and then there are very many of these

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kind of complicated substructures

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so that that drug-based substructure we

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found

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somewhere down here there's very very

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very few biochemical compounds

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that have this substructure so this is

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very similar to a power law pattern we

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see this in other forms

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of life so i'm not really going to get

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into that too much but

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this is potentially a distinguishing

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significant future of life

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um and i think thankfully

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um the three domains of life when you

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start looking at

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genomes accessed through the joint

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genome institute

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and start linking them up with the

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compounds that those genomes have be

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able to say that the three domains of

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life are pretty similar

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so this is able to one say life is

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similar which is good

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if those domains are all over the place

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this would be a little hard to

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distinguish

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and my other data set was

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technologically produced chemistry so

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take data from

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re-access which we have access to via

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the collaboration with the university of

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glasgow

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and i'm able to say reaccess has

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very very few shared compounds just

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noted it just drops off precipitously

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and there are very many compounds or

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substructures

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that are shared throughout there are

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very many substructures that are not

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shared

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so see it's technologically produced

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chemistry is less

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shared than biology

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which which is interesting um shows that

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if something has this kind of not

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shared pattern um probably doesn't have

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this evolutionary history of what

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chemistry does

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that's my initial hypothesis um

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what's kind of saying that here is that

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biochemistry is more shared

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substructures

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than a non-living technology to produce

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system

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a few caveats that reaccess is primarily

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a pharmaceutical database

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there's a lot of materials science and

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there's a lot of weird metal chemistry

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going on there

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but a significant portion is

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pharmaceutical based so it is

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biochemical adjacent um it's not what's

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made in biochemistry

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next steps the most common substructure

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algorithm is not the only way we can do

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this

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um one of the reasons i am here in

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glasgow is to study molecular assembly

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fragments

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which um there's a paper that just came

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out

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how

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assembly theory can be used as a

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potential biosignature

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and it's also a preprint which will soon

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be published in science advances

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of looking at modular assembly as a way

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to

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evolutionarily related compounds

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um essentially it makes fragments as

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well you're able to break down

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components

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or to break down the chemicals into

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component fragments

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assembly theory builds them back up here

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it's looking at the fragments i'm

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curious to see how they compare with the

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mcs algorithms

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any questions on this stuff specifically

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let me know and we're very happy to talk

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the what i'm trying to say but i think

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my goal is is to say

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um chemical agnostic measures can serve

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as the basis for identifying

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these limitable these these living

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chemical systems

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i think you need to have something

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that's chemically agnostic i think

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you're not able to distinguish chemical

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systems if you're looking only at

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biochemistry because you get a little or

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because you get biased with what earth

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chemistry has to offer

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um we won't know what chemistry looks

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like in other planets

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um and i think in order to have a full

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debate about what life is

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in order to distinguish life from

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chemistry you need to make sure it's a

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um work with sarah walker at arizona

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state university so thank you to her for

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helping me with this um working with lee

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cronin and glasgow

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certainly been an interesting few weeks

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so far

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and really excited to continue working

295
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here everyone in the

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arizona state lab everyone that i've met

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so far in the cronin group

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and also for thank you for that crack at

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grad con

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opportunity um to present here and

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meet everyone it's a wonderful

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conference i'm always having a lot of

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fun