Richard Sear University of Surrey

Richard Sear

University of Surrey

Phase Transitions: From the Big Bang to Biology

Phase Transitions:

Around us.

In general.

In the universe.

In biology.

Plan

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

pdf for speed of Na atoms

Almost all phase transitions are driven by interactions between the molecules, quarks, etc.

The exception is Bose-Einstein condensation.

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 the Early Universe

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

When Dvl is mutated cells can’t polarise – so hairs point randomly

Close up of part of wing of fruit fly (Axelrod)

Normally hairs point away from body

A protein called

Dishevelled

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

A protein called

Dishevelled

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

Measure of biological function

Bienz lab

No phase separation – no function

mutant

A Phase Transition

in a cellmutantnormal

Interactions

engineered

Molecular interactions set by laws of physics

Protein interactions optimised by evolution

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

David Goodsell

30 to 40 % by volume protein and RNA