Richard Sear University of Surrey

Phase Transitions: From the Big Bang to Biology Richard Sear University of Surrey

Plan Phase Transitions: • Around us. • In general. • In the universe. • In biology.

Around us: Water Water vapour transformed to liquid water.

Phase transitions are universal Annual rainfall (mm) New Haven London

Phase Transitions: Symmetry Crystals are not isotropic – here the snowflake (ice) has hexagonal symmetry On freezing the isotropic symmetry of the liquid has been broken. Ice is less symmetric than water.

Phase Transitions: Sudden Phase transitions are sudden, dramatic, phenomena On heating water, nothing happens until suddenly at 100 C it boils.

Phase Transitions: Collective phenomena One, or a few, molecules: No phase transition. A single molecule cannot boil, cannot freeze.

Phase Transitions: Collective phenomena Only with many molecules can water and ice exist.

The exception that proves the rule Almost all phase transitions are driven by interactions between the molecules, quarks, etc. The exception is Bose-Einstein condensation. pdf for speed of Na atoms

Phase Transitions: In the Early Universe Quark-hadron transition from fluid of unconfined quarks and gluons to one where they are bound in hadrons. Image from QCD conference in Adelaide – Wilton can explain?

Phase Transitions: In the Early Universe Universe expands and cools 10 μs

Phase Transitions: In Biology Fluorescent image of cells – nuclei are blue.

A protein called Dishevelled Dictionary definition: Dishevelled, adjective(of people or their appearance) very untidy

A protein called Dishevelled When Dvl is mutated cells can’t polarise – so hairs point randomly Normally hairs point away from body Close up of part of wing of fruit fly (Axelrod)

A protein called Dishevelled The protein dishevelled (Dvl) is essential for development in all animals.

A Phase Transition in a cell Nucleus Cytoplasm

A Phase Transition in a cell Dvl is NOT uniformly distributed in the cytoplasm of the cells. It forms dynamic aggregates, called puncta. Scale bar 15μm Dale lab, JCS 2005

Defending against HIV attack The protein TRIM5α (green) & microtubules (red) TRIM5α also forms dynamic aggregates. These defend the cell against HIV. Hope & Stoye labs

Defending against HIV attack Movie Hope & Stoye labs

Defending against HIV attack TRIM13 (green) & nucleus (red) Ballabio lab

A Phase Transition in a cell mutant mutant normal No phase separation – no function Measure of biological function Bienz lab

Interactions engineered Molecular interactions set by laws of physics Protein interactions optimised by evolution

In cells phase transitions Perform a function Melting of ice, formation of baryons just are – consequence of laws of physics In biology they perform a function – consequence of evolution

Phase Transitions: Symmetry Water droplet in 0g (NASA) Liquids are isotropic – droplets spherically symmetric

The cytoplasm is crowded 30 to 40 % by volume protein and RNA David Goodsell

Richard Sear University of Surrey