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Alan Ward
Molecular Microbiology
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Evolution
What is the structure of life?
Alan Ward
Evolution
Depth first or breadth first
Two different strategies for computer search algorithms
Which 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)
Evolution
• 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 thermodynamics
Energy is neither created nor destroyed
but reactions, in which energy changes, still occur
2nd Law of thermodynamics
Systems change from ordered to disordered
but living things are highly ordered
ΔG = ΔH - TΔS
Evolution
Why did life evolve?
1st Law of thermodynamics
Energy is neither created nor destroyed
but reactions, in which energy changes, still occur
(NH4)2SO4
Processes proceed from
High energy to Low energy
But the 1st Law of Thermodynamics
Direction ofEnergy
chemical
change
but
not
always
is neither
created nor
destroyed
often corresponds to -ΔE
Why did life evolve?
2nd Law of thermodynamics
Systems change from ordered to disordered
ΔG = ΔH - TΔS
A+B
C+D
[A][B]
o
ΔG = ΔG + RT loge _____
[C][D]
Glyceraldehyde-3-P = dihydroxyacetone-P
ΔGo = +1.8 kcal
[G3P] = 3 x 10-6M
[diOHAcP] = 2 x 10-4M
ΔG = 1.8 + 1.98x10-3x298xloge(3x10-6/2x10-4)
= - 0.7 kcal/mol
Early Earth
Hot (>100oC) Meteorite bombardment Volcanic
Gases – H2O CH4 CO2 N2 H2S/FeS HCN CO H2
Energy sources
virtually no O2
Primitive atmosphere + energy
(heat, UV, electric discharge)
UV light
Pre-biotic synthesis
of bio-molecules
Polypeptides, polynucleotides
Amino acids, purines,
pyrimidines, sugars ..
Energy and life
Spontaneous direction of change
Times’ arrow
H2O
CO2
It doesn’t go backwards
Kept warm but no
net energy in
Simple
High energy
Ordered
Organic
Low energy
Disordered
inorganic
Complex
More ordered
Evolution
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
Living organisms are highly complex
and ordered = low entropy
but create disorder = high entropy
CO2 ΔSenergy = high
+ H2O
Simple mixture of
proteins
ΔSegg = moderate
Net ΔE = 0
ΔSchick = low
Net ΔS = positive
ΔG = -ve
Evolution
Living organisms are highly complex
and ordered = low entropy
but create disorder = high entropy
CO2
ΔSenergy = high
+ H2O
Simple mixture of
proteins
ΔSegg = moderate
Net ΔE = 0
ΔSchick = low
Net ΔS = positive
ΔG = -ve
Evolution
= low E high S
= higher E lower S
more disorder – higher ΔS
Evolution
ΔG is negative
but it doesn’t say
how fast!
Evolution
Evolution of the Universe  Entropy increases
Life catalyses the rate of increase in entropy in the Universe!