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0:00
My name is John Torday,
I'm a Professor
of Evolutionary Medicine
at UCLA.
The title of this lecture is
"The Unicellular Origins
of Complex Physiology".
0:12
Sterols and membrane fluidity
in prokaryotes and eukaryotes.
Sterols play a fundamental role
in membrane fluidity
in determining interactions
between the external
and internal environments
of the cell.
Bacteria express hopanoids,
which determine the structure
of the cell membrane.
Eukaryotes express cholesterol,
which plays the same role
that hopanoids do
in the cell membrane.
0:39
Ancient atmospheric
oxygen levels,
shown in frames
A and B of the slide,
had to have been high enough
to allow the biosynthesis
of cholesterol.
It requires 11 atoms of oxygen
to synthesize
1 molecule of cholesterol.
The insertion of cholesterol
into the eukaryotic
cell membrane
fostered
the basic characteristics
of vertebrate evolution,
metabolism, respiration,
and locomotion.
Subsequently,
the cell membrane cholesterol
formed lipid rafts
that formed the sites
for receptors
that mediate
cell-cell interactions.
Ultimately,
cholesterol was the substrate
for the steroid hormones
and vitamin D,
which are a large part
of the endocrine system
that integrates and orchestrates
physiologic functions.
1:21
The polycyclic hydrocarbons
that were contained
within asteroids, snow balls,
that pelted the early Earth,
devoid of oxygen to burn them up
upon entry into the atmosphere,
were suspended
in the early nascent oceans.
Lipid emulsions in an aqueous medium,
spontaneously generate micelles,
semi permeable membrane
bound spheres.
Within these spheres
chemiosmosis,
the partitioning of positively
and negatively charged ions,
would have generated energy
to reduce the endogenous entropy
of the protocell.
Homeostatic control
of the system
would have sustained
the negative entropy of the cell
far from equilibrium.
The subsequent rise
in oceanic calcium
due to the increased amounts
of carbon dioxide
in the atmosphere
dissolving in water
to form carbonic acid,
which leached calcium
from the ocean floor,
threatened the existence
of early life on Earth,
since calcium ions
come up lipids,
proteins, and nucleotides,
the essence to life.
In response,
lipids were employed
to form calcium channels
to regulate the flow of calcium
in and out of the cell.
Subsequently,
peroxisomes evolved to buffer
the deleterious effects
of increased cytoplasmic calcium
caused by physiologic stress.
The epistatic balancing
of calcium by lipids
has evolved
over biologic evolution
as the fundament
of vertebrate physiology
and pathophysiology.
