Surprise, surprise

Due to the complexity and smallness of the organelles inside the cell, I thought I should devote a whole tab in the interactive to describing them visually. I decided to start with an organelle that I expected to be easy: the mitochondrion. It turns out, since the late 1990's, there has been a revolution in the way that people think of mitochondria.

In the 1950's, the transmission electron microscope became a fashionable tool for inspecting cells, and it allows extremely high resolution, but the problem is that it can only examine a very thin slice of the cell. A problem arose when trying to determine the 3D structure from 2D information. There were two cytologists who were simultaneously trying to describe mitochondria. Dr. Sjostand had a more painstaking tissue fixation technique, while Dr. Palade didn't believe that the conditions of fixation were important. Their observations led them to different conclusions about the morphology of mitochondria. Dr. Sjostand insisted that the foldings of the inner membrane (called cristae) were only continuous with the rest of the membrane in very small areas, while Dr. Palade beleived that they were like the baffles of an accordion, and were continuous with the inner membrane over large spaces.

While they both agreed that Dr. Sjostand's micrographs were better, and Dr. Sjostand's fixation method has become universally adopted, Dr. Palade's baffle model was the one to become widely accepted, and it is still in most textbooks today. It wasn't until the late 1990's, when microscopy techniques were developed that allowed the examination of thicker slices of cells, that people noticed that mitochondria look nothing like Dr. Palade's model, and Dr. Sjostand was more correct about mitochondrial internal structure. The cristae are tubular in the cells of almost all tissues, and are indeed only connected to the inner membrane by small round openings, now termed "crista junctions."

But what about the external structure and overall morphology? Better microscopy has revealed that mitochondria are not usually isolated, bean-shaped entities, floating in the cytosol, but that they form a dynamic network of interconnected mitochondria that are constantly coming together and separating, based on energy demands of the cell. Also, they associate closely with the endoplasmic reticulum.

Because this information about mitochondria took me by surprise, I have decided that a good deal of reading must be done before I can draw any organelle, because I want my interactive to have the most up-to-date and accurate pictures, and not to show the generic, formulaic representations that I have been seeing all my life. So, don't be surprised if you see something represented in a way that you are not used to seeing it.

The interactive will be online soon, although this business with the mitochondria and other organelles has slowed me down somewhat...But I think it is better to do more research and invest more time in the beginning, than to have to go back and make changes later.

What color is a cell?

Because most cells are invisible to the naked eye (with some exceptions, like the chicken egg which is all one giant cell) the scientific artist has to choose what color to make them. For the illustrations of cells in my project, I am going to use a color palette derived from pictures of cells that are stained with H & E, or hematoxylin and eosin. This combination of dyes is very often used to visualize cells for light microscopy. In fact, at a previous job, I personally spent many an hour in the lab at a microscope counting H&E-stained lung cells. Because of this tradition, it seemed like an appropriate choice for use in my project.

Click here to see a picture of cells stained with H&E. To make a long story short, hematoxylin is a dark blue-purple dye that is basic. It stains regions rich in DNA and RNA, such as the nucleus and ribosomes. Eosin is bright pink, and stains cytoplasmic protein.

For my illustrations, I created this palette by using the eye-dropper tool in Photoshop to sample the various colors from a few examples of H&E photomicrographs. The colors on the left are used for the color inside the cells, the second row is used for the stroke defining the edges of the cells, as well as organelles and details inside. The 3rd row is for the nucleus, and the last row is for highly eosinophilic structures like erythrocytes, or the bright pink spheres inside an eosinophil, which is what gives them their name.