BIO 1130 Lecture Notes - Lecture 7: Central Dogma Of Molecular Biology, Rich Mix, Eukaryote

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7 Aug 2016
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BIO1130 – Lecture 7
Prebiotic organic chemistry
To understand the origins of life on earth we’re faced with a couple of realities.
Life on earth is based on the versatility of the carbon atom to form the carbon-
based compounds that are the basis of all living molecules. A second reality is
that simple carbon molecules came first followed by the more complex. In short,
biomonomers preceded the biopolymers and all of this occurred in the water of
those ancient oceans. The question then becomes what are the origins of these
first monomers?
Organic chemistry is all about carbon and attaching things to it. This was the first
type of chemistry to occur in the ancient oceans as carbon atoms were linked
together to form the biomonomers of life. One of the first plausible explanations
for how this occurred was the Miller experiment. The presumed primordial gases
of methane, ammonia, and hydrogen were combined in a glass container and
water (a surrogate for the ancient ocean) was boiled causing hot vapours to rise
into the gas mixture. The resulting vapours were cooled and condensation
occurred (ancient rain) and the condensate fell into the pool of water that was
being heated into water vapour. Miller added electrical sparks, (ancient lightning)
to the mix of gases and let the whole thing run for a number of days before seeing
what had happened to the initially pure water. He found amino acids, a variety of
carbon compounds; even some lipids had been formed. After these experiments
were done it’s became clear that carbon dioxide was also present in the ancient
atmosphere and it’s inclusion in Miller’s original mix doesn’t change the most
significant result; that biomonomers could be produced spontaneously in the
earth’s early atmosphere. This experiment has been repeated under a variety of
different conditions and with different starting materials and the results give us
essentially every organic building block with the exception of one – the
nucleotide of either RNA or DNA.
This potential source for the first organic molecules remained unchallenged until
explorations to the ocean depths revealed an alternative source for the initial
organic compounds. In the deepest parts of the ocean, often kilometers deep, the
crust of the earth is thin and the continental plates separate from each other. Here
the hydrothermal vents occur where the core of the planet releases gasses and
molten rock. The temperatures are in the hundreds of degrees Celsius but the
water doesn’t boil because of the tremendous weight and pressure of the miles of
water above the vents. Instead it heats to temperatures higher than the usual
boiling point and remains liquid. The result is a brew of organic molecules and
another source for the organic molecules as the precursors to the biopolymers of
life.
Our understanding of the events in the ocean depths has lead to speculation that if
water were present on another planet and under the same conditions as the vents,
then organic molecules may have arisen elsewhere in the solar system. If so then
during that building stage of the Hadean some of the large meteorites that hit the
earth may have contained organic matter! Comets often have a large core of
frozen water. Is it pure, or a sample of the primordial soup from another planet?
The destructive heating of the planet wouldn’t have destroyed these compounds
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