Parasite Eve (20 page)

    Her heart again.

    THUMP.

    This was it. Kiyomi realized
it now. This was what her heart had reacted to. Her heart thrilled to
mitochondria.

    But why?

    Kiyomi’s eyes were riveted to
the screen, her breath short. She stared intently at the large image before
her, forgetting everything else around her. A few more pictures of stained
mitochondria were shown. Some green, some blue, they swelled beyond the screen,
twisting, dissolving, breaking away, changing into variant forms. She was
fascinated by their structure. Their wriggling, winding forms resembled
intestinal bacteria, and she understood why the professor was comparing them to
parasites.

    He said there was DNA in
mitochondria, that this DNA differed from DNA in the nucleus, and pointed out
that mitochondria were proven to be the descendants of what were once parasitic
bacteria. Ishihara also explained in detail that long ago, back when we were
still delicate single-celled organisms, mitochondria invaded us, and have since
thrived in symbiosis.

    “At this point I’d like to
talk a little about the history of cell development. Life is first thought to
have appeared on this planet around 3.8 billion years ago. The first life forms
were simple, pliant membranes containing DNA that dwelled near underwater
volcanoes on the ocean floor, receiving nourishment in the form of hydrogen
sulfide. At this time there was still almost no oxygen in the earth’s
atmosphere. However, 2.5 billion years ago, these first life forms evolved into
so-called cyanobacteria, a rudimentary form of chloroplasts. They created
sugars from photosynthesis and were the first organisms to, in essence, ‘breathe’
oxygen. Cyanobacteria multiplied at an extraordinary rate and spread throughout
all the world’s oceans. Because of this, oxygen levels rose both in the water
and the air. But the old type of bacteria which lived off of sulfuric gases
began to suffer. Unlike us, they were actually threatened by the growing
presence of oxygen in the sea. The world had become the domain of
cyanobacteria, leaving their less evolved counterparts no other choice but to
limit their quiet existence to their beloved sulfur-rich areas. It was at this
point that aerobic bacteria came into the picture. As I said before, the ocean
was teeming with oxygen created by cyanobacteria. What aerobic bacteria did was
find a way to make use of this oxygen; they became the early ancestors of
mitochondria as we know them today. By utilizing the oxygen around them,
aerobic bacteria were able to produce energy far beyond the capacity of normal
bacteria. The purpose of that energy? Mobility. These bacteria were the first
to actually swim around in the sea. And then, 1.5 million years later, a most
amazing event occurred when aerobic bacteria entered the bodies of our distant
ancestral life forms, who were barely surviving near volcanoes. It is possible
they originally wanted to consume us, but chose instead to make their home
inside of us. From that moment on, our relationship with mitochondria began.”

    A photograph of a single
mitochondrion appeared, this one taken through an electron microscope. Situated
in the middle of the screen, it was constricted in its center, about to divide.
There was a small black mass inside of it which appeared to be pulling into two
halves as well. Ishihara pointed this out as DNA. Mitochondrial division and
multiplication happened inside the cell. The DNA was distributed among the new
mitochondria. In all this, mitochondria seemed no different from, precisely,
bacteria. Kiyomi thought to herself,
Mitochondria are alive and they’re
multiplying inside of my body right now
.

    “Now what would you say if I
told you it is because of mitochondria that we are all here today? As I said
before, our earliest ancestors lived in a symbiotic relationship with
mitochondria and were able to produce vast amounts of energy. They became
aerobic, which in turn gave them the advantage of volition. From this they were
able to take sustenance by their own means, instead of having literally to wait
for it to float by. Using their own energy, they could go looking for it
themselves. Now here, our ancestors acquired a new level of intelligence,
namely the capacity to capture prey by any and all means necessary. They
figured out how to most efficiently obtain their food. Nerve connections
responsible for conceptualization and instinct began to develop, and, before
long, they acquired a rather advanced way of thinking.

    “We must not forget that,
around the same time, mitochondria were not the only living matter to be
incorporated into cellular life forms, but that some cells also combined with
cyanobacteria. And what happened to them, you might ask? They became
self-sustaining organisms that required only sunlight for survival, without
needing to go through all the trouble of searching for food. All they had to do
was to maximize their surface area to catch as much sunlight as possible. I am
sure you have figured out by now that these became plants. Though this
explanation may be a bit diluted, now you know the basic difference between
plants and animals. We can say with relative surety that our ability to move
and think as we do is solely the result of our symbiosis with mitochondria.”

    The professor then began
explaining the evolution of all living things as he pointed to a map outlining
just that. At the base of the diagram was a thick trunk labeled “Our Ancestral
Life Forms” which joined up with another trunk labeled “Mitochondria.” From
there, they separated into three paths: “Plants,” “Animals,” and “Fungi.”
Halfway up, the “Plants” branch merged into one line with “Chloroplasts,”
itself extending from the “Cyanobacteria” trunk. Kiyomi thought the
“Mitochondria” trunk looked the most robust in the diagram.

    The image on the screen
returned to the previous photograph of mitochondria, and Ishihara continued.

    “However, as they are now,
mitochondria do not have the ability to multiply at will. To this very day, we
have no idea exactly how mitochondria divide. What we have concluded, through
extensive research, is that they are somehow controlled by genes in the
nucleus. When mitochondria first parasitized our cellular ancestors, they must
have had an inherent genetic code which told them to propagate. But soon,
mitochondria inserted this code into the nuclear genes of their hosts. And so
now mitochondria have only a fraction of their original genetic code left. The
processes by which mitochondria divide, as well as the creation of the proteins
that comprise them, all begin with the nucleus. Mitochondria therefore put
their all into producing energy. From their point of view, they have it pretty
easy, considering that the nucleus does all the hard work. The sugars and fats
needed to make energy are provided by the host cell. Things aren’t bad for the
host cell either because, supplied the materials, mitochondria create
high-quality energy that the host could never generate on its own. In short,
mitochondria have sustained an excellent symbiotic relationship with their
hosts’ cells since long ago, much in the same way that we do with intestinal
microbes.”

    At this point, Ishihara
paused to take a sip of water.

    Kiyomi’s heart was beating so
fast, it was about to jump out of her chest. She had been too enraptured to
notice that she was panting like a dog, her mouth hanging wide open. She became
aware of herself when the professor stopped. She was surprised at her behavior
and swallowed her saliva with a gulp. Her heart pounded away like there was no
tomorrow. Having no other way out, her breath escaped audibly from her nose in
a steady rhythm. Kiyomi was ashamed. She covered her face with her hands,
trying to quiet herself as much as she could. She shut her eyes and took a deep
breath.

    She was confused. Why did she
have such an interest in all of this? Why was she so enchanted by it? These
were questions for which she had no answers. Kiyomi’s forehead was dotted with
sweat, as were her chest and inner thighs. Her dress clung to her skin. She
wiped her forehead with the back of her hand, where the sticky sensation
remained.

    Kiyomi opened her eyes,
removed a handkerchief from her pocket, and dabbed her neck and forehead. When
she looked back to the screen, Ishihara was discussing mitochondrial DNA,
explaining how it brought about abnormalities associated with the aging
process. This had to do with something called active oxygen. The genetic
mutations in mitochondria, he explained, were responsible for many diseases. He
then moved on to the inheritance of mitochondrial genes by our descendants.

    “Mitochondrial genes are
interesting in that they are passed along by the mother. At the time of
conception, mitochondria in the sperm enter into the egg as well, but in most
cases this paternal DNA does not multiply in a fertilized egg. Because only
maternal DNA reproduces, the mitochondria of any given child are nearly
identical to that of its mother. As a result, the genes are ultimately passed
down matrilineally. Even so, diseases caused by mitochondrial genes are not all
inherited from the mother’s side. This is a mystery not even current research
has been able to clarify. We have only recently come to know that the genes are
not passed on entirely maternally. This is a rather complicated issue, so let
us move on.”

    The rate of pictures
decreased, changing to brightly colored graphs and various other diagrams.
These images looked to have been rendered by computer, and did not excite
Kiyomi as much as the microscope photography. The professor continued talking
about mitochondrial genes for five minutes. In the meantime, Kiyomi’s heartbeat
slowed down from its violent pounding to a more subdued pace before eventually
returning to normal.

    She breathed a sigh of relief
and sat upright, trying her best to concentrate on Ishihara’s lecture as he
moved on to the next subtopic.

    “...We have all experienced
stress, whether with the people we encounter in school, at home, or in the
workplace. Ours has been called the most stressful age in the history of
civilization, but I believe stress is simply inevitable, once we have the very
act of sharing our lives with those around us. This is very much similar to the
relationship between mitochondria and their host cells. When two different
entities live in a sealed environment, stress is created. In fact, as stress is
exerted upon the cells, so-called ‘stress proteins’ are activated within them.
These proteins allow the symbiosis between mitochondria and the nucleus to run
smoothly.”

    Ishihara proceeded to
explain, with the use of simple visuals, that there were various types of
stress proteins within cells, that one of their jobs was to move enzymes into
mitochondria, and that when stress proteins died off, this resulted in
mitochondrial mutations.

    Kiyomi’s heart was now
perfectly at ease. She looked at her hands, only to find they were knotted
tightly, the only indication of the agitation she’d experienced. She opened and
closed them a few times to loosen them up and smiled to herself.

    Just then, the screen changed
yet again, and a large bar graph appeared. Ishihara explained these were the
results of their lab experiment. They had examined the degree to which enzymes
were still transferred into mitochondria when stress proteins were
systematically affected. The horizontal axis named the various stress proteins,
from which extended bars of varying heights.

    “From this we can see that
when some of the stress proteins decay, mitochondria become unable to produce
enzymes sufficiently. This lack of mitochondrial function appears to be linked
to many diseases.”

    Kiyomi was staring at the
screen, following the bright red dot of Ishihara’s laser pointer. After he had
finished and told the assistant to move on to the next slide, Kiyomi happened
to notice something small written in Roman alphabet in the bottom right hand
corner.

    Her chest popped: WHUPP!

    It came so abruptly that she
let out a small cry and pitched herself forward. The slide projector clicked
again and another bar graph appeared on the screen. Kiyomi ran her eyes frantically
from corner to corner and found the same letters written there. Again, her
heart erupted. Professor Ishihara went on, but Kiyomi could no longer hear what
he was saying. Again, the click of the projector. Again, the screen changed to
another bar graph. Surely enough, the same letters on the bottom right hand
corner. Three times, this intense jolt swept through her. Her body lurched
audibly off her seat. She felt everyone’s eyes on her, but could make out none
of them in her daze. Her heart was going to explode. Kiyomi clutched her chest
in a desperate attempt to calm herself. She opened her mouth and tried to
speak, but only a painful wheeze escaped. Her breaths grew shorter by the
moment. Her face was on fire, her heart was thundering. Somewhere in the jumble
of her mind, she | tried frantically to rationalize what was happening to her.
The fine- printed lettering on the screen. Kiyomi had not even read it all. In
a brief moment of lucidity, she strained to remember what it said. [Everything
was turning foggy. Someone ran up to her. She remembered now. The words floated
into her mind’s eye as clearly as the pulse throbbing inside her brain:

   
Nagashima, T. et al.
J. Biol.
Chem.
, 266, 3266, 1991.

    There was something familiar
there, something in that name. T.
Thump
. To-shi-a-ki. Yes, that was it.
Thump
.
TOSHIAKI NAGASHIMA.
Thump
. She had heard that name before. She knew him
from somewhere. Of course, she thought, he’s the one I met when I first came to
college... Thump, THUMP,
THUMP
.