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my

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the modern cell is a very complex system

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consisting of many parts

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which perform very specific functions

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we've learned a lot about how

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the cell works in the last 20 or 30

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years but there's still more

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questions to be answered one of these

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questions is how exactly the

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initial cell emerged and evolved in the

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first place and one of the hypotheses is

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that a primitive compartment

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or otherwise known as a protocell was

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the first form that eventually evolved

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into modern cells

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this leads us to origins of life

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research where we focus on how

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the chemistries available on early earth

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also known as prebiotic chemistry

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assembled into the first compartments on

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earth and how these compartments

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evolved into modern cells

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compartments in particular are very

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crucial to the origins of life

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as they perform a number of very

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essential functions to

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a primitive system such as concentrating

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and segregating reactants

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one process that allows primitive

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compartmentalization

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is liquid-liquid phase separation this

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process

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results in the formation of

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membrane-free droplets similar to

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colloids or other soft matter and these

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droplets can allow

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compartmentalization and exchange of

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molecules between phases

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in fact phase separation is present in

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biology where a number of

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membraneless organelles exist in our

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modern cells such as

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stress granules or chromatin

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one of the systems that we like to study

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as model systems that are

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liquid liquid phase separated are called

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complex coaster rates

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these structures are formed from the

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binding of oppositely charged

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biopolymers such as

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a positively charged peptide and a

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negatively charged nucleic acid and the

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result is

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a membraneless droplet concentrated in

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both of these phases

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coastal rates actually perform a number

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of very

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important primitive functions such as

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the ability to concentrate

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biomolecules such as nucleotides or

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nucleic acids

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coaster rates have also been shown to

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grow and divide through external forces

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such as

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physical agitation or electric fields

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coaster rates can have their structural

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complexity increased

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through the assembly of multi-phase

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compartments each with very specific

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chemical affinities

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and also coaster rates can scaffold

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membrane assembly

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suggesting perhaps one transition state

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between

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a membrane list and a membrane-bound

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primitive compartment

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in our studies we focused on

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another way to potentially increase the

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structural complexity of coastal rates

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and this is through the incorporation of

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dna liquid crystals

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short duplex oligomers bind together and

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aggregate end to end forming these long

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stiff rods these stiff rods

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actually will bundle together forming

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these nice

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patterns that can be observed in

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polarization microscopy and we sought to

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combine this liquid crystal structure

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with a coaster rate structure

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through the addition of a cationic

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indeed we noticed that through addition

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of polylysine to these dna structures

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we were able to find the co-localization

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of liquid crystal structures

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seen below and the membraneless droplet

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structure seen above through the

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different types of microscopy

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this structure is likely caused by the

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end-to-end stacking interaction

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of these dna duplexes interacting with

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the polylysine peptides

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so we actually were able to find these

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structures but they're actually

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only exist under very specific salt

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conditions

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here we show that the structure of these

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liquid crystal coaster rate structures

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as we call them is modulated

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through the modulation of sodium

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chloride

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so for example at lower concentrations

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of sodium chloride

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what we see are precipitate-like

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structures at 800 millimolars

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we see of sodium chloride we see

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co-localization

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of the liquid crystal coastal rate

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structure and through

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increasing sodium chloride we see first

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the disassembly of the liquid crystal

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structure

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followed by the disassembly of the

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droplets themselves

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we believe that this

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property is due to the fact that

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increasing salt concentration

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will help to shield the interactions

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between the

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cationic peptide and the anionic dna

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backbone suggesting that

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higher salt concentrations result in

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less interaction between those polymers

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and lower salt concentration results in

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stronger interaction between those

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polymers

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we also did an experiment where we

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engineered a dna duplex but with

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two base overhangs and so this structure

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actually resulted in the formation of

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coaster vates but no liquid crystal

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structures and we believe that this is

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because

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the 2t base overhang actually inhibits

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the

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processes on early earth could have also

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modulated the structure of these liquid

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crystal coaster rates and here we

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subjected the liquid crystal coastal

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rate structures to dehydration

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a process that could have been affected

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on earlier

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through for example evaporation caused

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by

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seasonal or day night changes so here

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we see from a to e first the existence

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of

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a precipitate-like structure this

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precipitate like structure transitions

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into a liquid crystal

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coastal rate structure shown in b and c

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and slowly

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through further dehydration the liquid

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crystal coaster rates

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of the liquid crystals start to

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disassemble resulting in

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only coaster based structures in d and

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finally in e we see that the

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entire coaster rate structure has been

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disassembled

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here is a video showing the similar

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and we believe that this process is due

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to the fact that

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the dehydration actually results in

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up concentration of the sodium chloride

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in solution such that

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by increasing the sodium chloride in the

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solution

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again similar to what we saw in the salt

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the salt titration experiments

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we see that the system transitions from

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precipitate to liquid crystal classivate

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to non-liquid crystal coastal rate to a

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next we wondered whether the system

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again could be modulated through

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various other primitive processes that

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would have been

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plausible and so here we study how heat

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can affect the structure of the liquid

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crystal classivates

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so we first started at 20 degrees

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upon bringing the system to 50 degrees

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we see

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very little structural change but

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upon bringing the system up to 60

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degrees we see a transition from the

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precipitate-like structures to a

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co-localized liquid crystal class survey

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like structure seen here and upon

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further increasing the temperature to 70

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degrees we see the liquid crystal

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structures

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disassembly disassembling resulting in

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only the

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non-liquid crystal coaster rate droplets

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we next decrease the temperature and so

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here we decreased the temperature

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to 50 degrees and no significant changes

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were seen

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upon decrease to 40 degrees we noticed

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that the liquid crystal classroots

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started to reappear and they were

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co-exist

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with the non-liquid crystal coaster

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rates seen here and so here in blue

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it's one type of liquid crystal the

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pneumatic phase and in red it's another

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type of liquid crystal the

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columnar phase upon further decreases in

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temperature we see more and more

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appearance of these liquid crystal

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coaster rate structures

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and finally decreasing the structure

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down to 10 degrees

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we actually see a majority of these

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structures being liquid crystal

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what's most interesting about this

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system is in fact that

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at very low temperatures before and

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after

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heating and cooling cycle the structure

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is very different for example

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at 20 degrees before heating and cooling

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we see

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predominantly the precipitate form

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whereas

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at 10 degrees after heating and cooling

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we see predominantly a liquid crystal

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coaster rate form

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and we believe that this is due to the

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fact that it's very likely that the

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liquid crystal class survey form is the

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most stable form and so

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the system requires a heating and

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cooling cycle or

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some other people also refer to this as

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an annealing cycle

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to find this most stable form

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so here's a summary figure showing what

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we believe is happening

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molecularly within these liquid crystal

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coaster rates

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upon increasing heat and salinity we see

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a transition in the phases first in red

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the existence of the columnar liquid

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crystal phase with the coaster rate

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phase where

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perhaps the dna rods in blue

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are interacting with the peptide strands

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in red and the rods have bundled

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together into hexagonal like

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forms increasing the heat and salinity

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results in the slight disassembly of

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these

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hexagonal bundles but still the

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existence of the rods

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and the interaction with the peptides

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suggesting the

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co-localization between here the

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cholesteric phase

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and the liquid crystal phase next upon

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further increases in heat insulinity

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we see the disassembly of these

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long rods resulting in shorter dna

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duplexes interacting with the peptides

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which results in formation of non-liquid

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crystal

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coaster rate droplets and finally upon

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high heats or high salinities the entire

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assembly

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disassembles so the dna no longer

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interacts with the peptides

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resulting in disassembly of the entire

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droplet phase

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so for those who are interested in

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learning more details about these

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studies

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here's information about two papers that

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were published last year

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they have a lot more details of the

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experiments that we performed and some

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of the theory

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that goes into these studies so i

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encourage you to

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look up these papers if you have more

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interest

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in learning some of the details

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so finally i'd like to thank all of the

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funding sources that helped to make this

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research possible including those from

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tokyo institute of technology

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jsps kakenhei japan astrobiology center

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and

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in particular this project was a

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collaboration

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through the french embassy in japan

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which was a part of a

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grant program called program exploration

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france which allowed

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a research travel grant to visit a

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collaborators

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research lab in paris so thank you very

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much for your time and attention

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i'm very happy to take any questions any

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time and please feel free to contact me

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by email