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*Please send it by TOMORROW (Jun 21) at 5 pm (Eastern Time Zone – USA).
Attached is a pdf of the case study Little Mito – The Story of Where He Came From. Your
assignment is to read the case study and answer the questions in the second document using your
textbook (particularly section 18.6) and reputible online sources. You should cite any outside
sources used in proper MLA format.
Some hints:
•
The autogenic hypothesis refers to the evolution of the nucleus and similar organelles.
•
When describing the weaknesses of the two hypotheses, consider the organelles listed
that are not explained by either hypothesis.
SCI 1015 – INTRODUCTION TO LIFE SCIENCE – ASSIGNMENT
Week 3
Little Mito Case Study
Questions:
1. What do the following abbreviations stand for? Describe each organelles function. (8)
a. Nuc
b. Flag
c. ER
d. Mito
e. Chlora
f. Golgi
g. Ves
h. Lys
2. What is the autogenic hypothesis of the origin of the eukaryotic cell? (3)
3. Explain at least 2 lines of evidence that support the autogenic hypothesis? (2)
4. What is the endosymbiotic hypothesis? (3)
5. Explain at least 2 lines of evidence that support the endosymbiotic hypothesis? (2)
6. What are the weaknesses of the two hypotheses? (2)
References:
Little Mito:
The Story of Where He Came From
by
Stephanie Vail and Clyde Freeman Herreid
University at Buffalo, State University of New York
Little Mito grew up in a one-room house in the Eukaryote family. His neighborhood consisted of oneroom houses just like his, and everyone got along real well. He grew up with his sister, Chlora, his older
brother, Flag, and his cousins, ER and Nuc. Each of them had their own chores, and the housework was
done quickly and efficiently as it came up.
Chlora was in charge of gathering energy and converting it to
carbon compounds and oxygen. She did this by soaking up the
rays all day, making carbohydrates in a process called
photosynthesis. It doesn’t sound like a tough job but everyone
knew she was the breadwinner in the family as long as the sun
was shining. If not, then it was up to little Mito to do the job. He
took his responsibilities seriously. He took the carbon
compounds that his sister had made and then broke them down
to get energy to run the household. He needed to breathe in
oxygen to do the job. He felt like he was a little furnace, burning
up the fuel and letting the energy out. Folks called what he did
“cell respiration” and it made him feel proud to know he was
doing his bit contributing to the family’s welfare.
Flag was the “mover and shaker” in the household. His job was to help the family move whenever they
felt the need to see the countryside. He accomplished this by poking his tail out of the house and doing
his undulating dance without a care for what the neighbors thought!
ER and Nuc had their own duties. ER was in charge of
distribution and storage. He maintained the household supplies,
seemed obsessed with moving things about in the house, and
always remembered Chlora, Flag, and Mito’s lunch money. Nuc
was the head honcho of the Eukaryote family, and his
responsibilities involved the organization of the family
documents and information and leadership. He told everyone
what to do and when to do it, even when they didn’t want to. He
was particularly busy on those occasions when they needed to
build a new addition to the house for their expanding family. But that’s another story.
The family was happy and set in its ways for many years until one day Mito heard a rumor about his
past. A friend on the playground mentioned something about his great great grandfather being in the
Prokaryote family. Mito wasn’t sure what this meant, but he knew it might be important, so he went to
the library to do some research. He never knew that genealogy could be so fascinating. But what he
found out was shocking and it troubled him greatly.
Page 2 of 3
Apparently, Mito had a questionable past. He almost felt illegitimate! There was a big argument among
academicians. There were two completely different ideas about his family’s origins: one was something
called endosymbiosis and the other was called autogeny. Autogeny was a familiar concept to him, being
as that was what he was taught his whole life. This was the legend that all of his relatives, Nuc, ER,
Chlora, and Flag, had come from a prokaryotic cell ancestor who got too big for his britches and decided
to infold his plasma membrane. This happened over thousands of generations. Slowly, but surely, he
folded his surface and produced a whole bunch of membranes inside the cell. Some of these pinched off
and made all of the family. As they floated around in the cytoplasm, they started to specialize with
certain tasks and household jobs.
This sounded reasonable to Mito; he was just a kid after all. He knew that Nuc had a swell double
membrane folded around him like a comfy blanket. Chlora and he also had double membranes, but their
insides were just chock-full of them too and these let them make energy for the house. And there was
ER and a bunch of other relatives like the Golgi cousins and brothers Ves and Lys. All of them were just
membranes, membranes, and more membranes. Then there was Flag. No one really knew where he
came in-they just didn’t talk about it. You know, a family secret.
But here was this other weird idea, endosymbiosis, that must have been what his friend was talking
about. The book he found stated:
Eukaryotes arose principally through a series of events wherein certain prokaryotic cells
were engulfed by other larger phagocytic prokaryotes, those whose membranes evolved the
ability to take in food through phagocytosis. Perhaps because digestive machinery was not
yet particularly efficient, or the prey had developed defenses against the predator’s
enzymes, some of the ingested organisms survived and continued living within the predator.
This was absolutely mind blowing! It contradicted everything that he had been taught in school about
his origins. Mito thought, “In the beginning, my great grandfather Mito wasn’t part of a family; he did
EVERYTHING ALL ALONE. And Grandpa was once an aerobic bacterium and not a Mito at all. Then
one day he got eaten by a bacterial predator and, according to this book, he was too strong for them. But
he found it was pretty cool living inside the predator. That’s my Grandpa! Always looking for a good
deal. As long as he did his share for the predator and kept producing extra energy, he was living in the
lap of luxury. He didn’t think of himself as a parasite or anything, it was more like a buddy system. I’ll
wash your back and you wash mine–that sort of thing.” In the book they called it a mutualistic
relationship.
But that wasn’t the end of it! The book said the predator host did it again and maybe even again. That’s
how his sister got here too. She had been a blue green alga who was gobbled up. “Awesome!” His
brother, Flag, the book said, maybe came from spirochetes who started living all over the host’s body.
The scientists weren’t real sure about that one though. Mito had always thought that Flag was a little
Page 3 of 3
strange. He was pleased to read that the book thought so too. All the books agreed that Nuc and ER
came about through traditional membrane infolding. If his cousins Golgi and the twins, Ves and Lys,
found this out he would never hear the end of it. “Good grief,” he thought, “I’m living with a bunch of
strangers. We aren’t related at all!”
Mito was shocked and disturbed, but most of all he was curious. What did this mean, and where did he
really come from? Which theory was the correct one?
Questions:
1. What are Nuc, Flag, ER, Mito, Chlora, Golgi, Ves and Lys short for? What does each of these
organelles do in a cell?
2. What is the autogenic hypothesis of the origin of the eukaryotic cell?
3. What is the evidence that supports the autogenic hypothesis?
4. What is the endosymbiotic hypothesis?
5. What is the evidence for the endosymbiotic hypothesis?
6. What are the comparative strengths and weaknesses of the two hypotheses?
Image Credit: Images obtained from “The Biology Project”, an online interactive resource for learning biology at The
University of Arizona.
Date Posted: 1/07/02 nas
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Tags:
Life Science
protein synthesis
Macromolecules
synthesized proteins
formation and rearrangement
cellular breakdown
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