Download 1. The non-living synthesis of simple organic molecules. 2. The

1. The non-living synthesis of simple organic
molecules.
Early Earth and oceans contained a mix of
D1: Origin of Life on Earth
inorganic molecules converted into simple organic
molecules. These organic molecules may have
been generated on the Earth or Space.
2. The assembly of these molecules into
polymers
Simple organic molecules polymerized into large
complex organic chemicals
3. The origin of self-replicating molecules made
inheritance possible.
Karl Popper argues that an hypothesis is not
scientific if it cannot be shown to be false. So
is the Origin of Life on Earth of “Scientific
value”?
Gases from the interior escaped by
volcanoes, forming an atmosphere of
Hydrogen (H), Water vapour (H2O), Methane
(CH4), Ammonium (NH4), Nitrogen (N2),
Sulfuric Acid (H2S) – there was no oxygen
(O2).
The mix of chemicals present in the oceans is
called primeval/primeordial soup or sea.
DNA and RNA can act as templates for copying
RNA self-replication does not require proteins/enzymes
Self-replicating molecules are subject to evolution by natural
selection
4. The packaging of these molecules into membranes with
an internal chemistry different from their surroundings
Formation of closed membranes is believed to be an early and
important event in the origin of cellular life
Closed membrane vesicles form spontaneously from lipids
separating inside from outside
Internal cellular metabolism then developed
The Earth was formed about 4.5 billion years
ago from dust around the Sun.
As the dust gathered size, gravity and
radioactive decay generated heat which
melted the center producing a core or molten
Iron and nickel surrounded by a cooler liquid
mantle. On top of the mantle is a crust which
formed the continents and sea floor.
This is called a Reducing Atmosphere
Miller and Urey conducted experiments in
1953 to see whether Chemical Evolution
could occur in primeval soup.
Chemical evolution is the sum of the pre-
biological changes that transformed simple atoms
and molecules into the more complex chemicals
needed for life.
Miller and Urey were able to form organic
compounds and amino acids and the
nucleotide base adenine!
Panspermia – hypothesis that life on Earth
may have originated by the introduction of
complex organic chemicals or even bacteria
via comets.
Cosmic radiation in deep space may provide
the energy to form complex organic
molecules.
How did Amino Acids and nucleotides
polymerize to form proteins and nucleic acids
Water favours polymer hydrolysis
Hydrothermal vents on seafloors called black
smokers allow superheated water from the
earth`s crust to enter the ocean. Black
smokers are rich in dissolved sulfides
Volcanoes help by fixing nitrogen for use by
early bacteria
Mars – because mars is small, it cooled
quickly which may have permitted prebiotic
evolution. Martian meteorites may have
brought these compounds to Earth.
RNA World Hypothesis – RNA played an
important role in the origin of life because it is
capable of storing information and of
replicating it
2. When RNA is replicated, mutations occur which
leads to variation, natural selection and this
evolution.
1. Ribozymes are small sequences of RNA that act
as enzymes to catalyse reactions of RNA
replication
RNA may have generated the first proteins
Eventually, RNA was replaced by DNA and
enzymes
Overtime, the complexity of organic
compounds in the primeval soup increased.
Coacervate – aggregations of polymers
Protobionts – the first precursors to cells
Protobionts may have evolved from
coacervates containing RNA
An internal environment can be
maintained separate from the
external environment
A major transition in evolution occurred when
bacteria evolved to contain chlorophyll which
allowed photosynthesis to occur and high levels
of oxygen were produced.
This is the Oxygen Catastrophe (2 billion years
ago)
This lead to a layer of ozone (O3) forming in the
upper atmosphere – this was a protective layer
from UV rays from the sun but it also stopped
the production of new organic chemicals in the
primeval sea
Endosymbiotic Theory – Chloroplasts and
mitochondria are derived from free-living
prokaryotic ancestors then they were
engulfed by larger prokaryotes
Evidence for the Endosymbiotic Theory:
M and C contain DNA
M and C are surrounded by double membranes
New M and C are formed by a process that
resembles binary fission
Internal structure and biochemistry of
chloroplasts are very similar to cyanobacteria
M and C contain ribosomes like bacterial ones
(70s)
Mitochondria evolved from Proteobacteria
Chloroplasts evolved from cyanobacteria
http://www.youtube.com/watch?v=Vgh2Eb8E2g
http://www.youtube.com/watch?v=3H0RXDrf
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http://www.allthingsscience.com/video/677/O
rigin-of-Life--Panspermia-1-of-3