I am a curious person. Sometimes things just pop into my mind and I think about them for a very, very, long time. I usually make lists of all the questions I have and that I sometimes hope to get an answer for. Today, Larry Moran at Sandwalk helped me get an answer for one of these questions.
During my first year of biology, we were learning about endosymbiosis, which means that a lot of the machinery inside our cells (like mitochondria or chloroplasts for plants) originated as separate organisms which where later engulfed by larger cells and started to reproduce within these larger cells. You may have heard that mitochondria carry separate DNA from yours which is only passed down through the maternal line in the cytoplasm of the eggcell.
When we learned about this, we learned that one of the indications of this was the double lipid layer of some of the organelles (machinery). I remember our teacher talked about how when the bacteria (mitochondria and chloroplasts are closely related to free-living bacteria) were engulfed in the cell, both the bacteria's own membrane and the membrane that enclosed the "engulfee" as it was passing into it were retained within the cell.
Let me explain that more clearly. A cell is covered by a membrane. When the cell eats or takes something up from the environment, it is similar to you sticking a marble into the surface of a balloon. The balloon covers the marble more and more, until this magic balloon breaks off a piece of itself to cover the whole marble which is then inside the balloon. Part of the balloon is now covering the marble.
What my teacher said was that as both these systems reproduced, the extra membrane of the balloon around the marble was retained through the generations and was still a sign of endosymbiosis.
I thought this was very strange. Usually when something enters the cell in this fashion, the membrane is broken down either after some time or "deliberately" at once to access whatever is inside. How could instructions to form an extra membrane around new organelles be incorporated into the genome of the larger cell or the organelle itself? Horizontal gene transfer?
I asked him after the lecture to clarify how this was possible, and he said it was an interesting question, but he didn't know.
Turns out the whole premise was wrong. (Thanks, Larry!)
Bacteria come in (very very roughly) two kinds. Gram positive and Gram negative. This property has to do with their membranes. Gram positive have a single membrane, and the Gram negatives have a double membrane. Guess which kind of bacteria are the origin of most of our double-membraned organelles?
This little story actually fit very well with another post by Mr. Moran, about the Dunning-Kruger effect.
The Dunning-Kruger effect should be familiar to most. It's sort of reminiscent of Socrates when he realized he was intelligent because he was aware of all the things he was ignorant about. Many people who have wrong perceptions or beliefs are not aware of the fact that they may be wrong. This is reflected in studies when people are asked if they believe they have knowledge on some subject or can perform a task at below average, average, or above-average levels. Many people who are below average are not aware of the problems in their thinking, and rate themselves as above average, and even above the people who are proved to be in the top percentiles. The people who are well-versed on a subject however, realize the limits of their knowledge and thereby rate themselves lower than the people who have the wrong ideas!
This reminds me of my own experiences in test-taking. Usually, if I have a good feeling, I get a disappointing grade, and if I have a bad feeling, I am pleasantly surprised. I think this is the same phenomena. When I have studied well, I am aware of my mistakes, but when I have a good feeling, it's because I don't even know what I'm wrong about or what info I am missing.
The fact that I asked that question of my teacher does not imply that I am a genius of course. Just that having a curious mind and asking questions about things that sound funny is generally a good thing.
Curiosity may have killed the cat, but it's really good for the scientific method!