Lecture 10: What is life? - Its Origins

Life’s machinery in a cell

A bacterial cell: RNA molecules transcribe messages from DNAthat are used to produce protein molecules inside ribosomes.

Structure of DNA

Earth life - main attributes:

1)life is chemical in essence; an ordered network of chemical reactions;

2)life is energy dissipating; out-of-equilibrium system;

3)life is compartmentalized;4)life is adaptive, self-optimizing,

fed back, forward; stable to perturbations;

5)life uses molecules that are suited to water.

DNA

RNA

proteins

Structure and function

replication

processing

processing

Organizational Complexity of Modern Life

RNA

biochemical functions

An earlier, simpler time:

Between non-life and life…

Viruses

Protocells

Self-replicating nucleic acids

What do we know about the Origin of Life?

From G.F. Joyce, 2002, Nature 418: 214-221

From Chemistry to Biology?

small molecules (CO, H2, H20, NH3, CH4…) + energy

lipids + sugars + nucleobases + high-energy + amino acids compounds

Self-assemblyinto vesicles

activated nucleotides

Assembly into genetic polymer

peptides

cofactors

protocell?

The simplest protocell requires a membrane for compartmentalization, a replicating genome, and a source of nucleotides and lipids.

Mechanical energy (for division), chemical energy (for nucleotide activation), and possibly osmotic gradient energy (for growth) may be used by the system.

Model of Simple Protocell

Matter and Energy Fluxes

The RNA World: Pre-biotic RNA formationJa

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The RNA World: Formation of VesiclesJa

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Why life needs a membrane compartmentJa

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The RNA World: Protocell life cycle & divisionJa

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Lipid bilayer vesicles in clay

RNA (red) adsorbed into clay, inside a vesicle (green) - Szostak lab (2004).

Earth life - main attributes:

1.life is chemical in essence; an ordered network of chemical reactions;

2.life is energy dissipating; out-of-equilibrium system;

3.life is compartmentalized;4.life evolves by natural selection

and inheritance of variation 5.life evolves to be adaptive, self-

optimizing, fed back, forward; stable to perturbations;

6.Earth life uses molecules that are suited to water.