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Alan Ward

Molecular Microbiology

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Multiple pagesViewing page 2

They give another example of why you need Data driven discovery as well as hypothesis driven research

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Slide 1

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Evolution

What is the structure of life?

Alan Ward

EvolutionDepth first or breadth first

Two different strategies for computer search algorithmsWhich is best?

That heavily depends on the structure of the search tree and the number and location of solutions.If you know a solution is not far from the root of the tree, a breadth first search (BFS) might be better. If the tree is very deep and solutions are rare, depth first search (DFS) might rootle around forever, but BFS could be faster. If the tree is very wide, a BFS might need too much memory, so it might be completely impractical. If solutions are frequent but located deep in the tree, BFS could be impractical. If the search tree is very deep you will need to restrict the search depth for depth first search (DFS), anyway.

Evolution

So what is the structure of living things that we are exploring?

The structure of life is dictated by evolution:

“Nothing in biology makes sense except in the light of evolution”

(Dobzhansky)

• How did life arise?

• How did it evolve?

• How is it evolving now?

Why did it evolve?

Evolution

Why did it evolve?

1st Law of thermodynamicsEnergy is neither created nor destroyed

but reactions, in which energy changes, still occur

Evolution

ΔG = ΔH - TΔS

2nd Law of thermodynamicsSystems change from ordered to disorderedbut living things are highly ordered

EvolutionWhy did life evolve?

1st Law of thermodynamicsEnergy is neither created nor destroyed

but reactions, in which energy changes, still occur

Processes proceed from High energy to Low energyBut the 1st Law of ThermodynamicsEnergy is neither created nor destroyed

Direction of chemical change

often corresponds to -ΔE

but not always

(NH4)2SO4

ΔG = ΔGo + RT loge [A][B][C][D]_____

A + B C + D

Glyceraldehyde-3-P = dihydroxyacetone-PΔGo = +1.8 kcal

[G3P] = 3 x 10-6M [diOHAcP] = 2 x 10-4MΔG = 1.8 + 1.98x10-3x298xloge(3x10-6/2x10-4)

= - 0.7 kcal/mol

Why did life evolve?

ΔG = ΔH - TΔS

2nd Law of thermodynamicsSystems change from ordered to disordered

Early EarthHot (>100oC) Meteorite bombardment Volcanic

Gases – H2O CH4 CO2 N2 H2S/FeS HCN CO H2

virtually no O2Energy sources

UV light

Pre-biotic synthesis of bio-molecules

Primitive atmosphere + energy (heat, UV, electric discharge)

Amino acids, purines, pyrimidines, sugars ..

Polypeptides, polynucleotides

Energy and life

Spontaneous direction of change

Times’ arrow

H2O

CO2

High energy Low energy

Organic inorganicOrdered Disordered

It doesn’t go backwards

SimpleComplexMore ordered

Kept warm but no net energy in

Vitalism

Living organisms possess a vital force that enables them to defy the laws of physics and chemistry.

In 1809 Berzelius stated the theory as that organic compounds could not be synthesized in a laboratory.

In 1828 Wöhler, whose mentor was Berzelius, synthesized urea, previously only obtained from biological sources, from inorganic reactants disproving the theory.

The second law may be expressed in many specific ways, but the first formulation is credited to the French scientist Carnot in 1824.

The first explicit statement of the first and second laws of thermodynamics was probably by Clausius in 1850.

Evolution

Evolution

CO2

+ H2O

Simple mixture of proteins

ΔSegg = moderateΔSchick = low

ΔSenergy = high

Net ΔE = 0 Net ΔS = positive ΔG = -ve

Living organisms are highly complex and ordered = low entropy but create disorder = high entropy

Evolution

CO2

+ H2O

Simple mixture of proteins

ΔSegg = moderateΔSchick = low

ΔSenergy = high

Net ΔE = 0 Net ΔS = positive ΔG = -ve

Living organisms are highly complex and ordered = low entropy but create disorder = high entropy

more disorder – higher ΔS

= low E high S

= higher E lower S

Evolution

ΔG is negative

but it doesn’t say how fast!

Evolution

EvolutionEvolution of the Universe Entropy increases

Life catalyses the rate of increase in entropy in the Universe!