Mitochondria are membranous organelles that are present in all eukaryotic cells except red blood cells and terminal keratinocytes. The numerous enzymes present in mitochondria are very important for cellular metabolism, and the number and shape of the organelles are largely dependent on cell type. It is widely accepted that mitochondria evolved from a prokaryote that lived in symbiosis with primitive eukaryotic cells. The primary support for this argument is the fact that mitochondria possess their own DNA and RNA. Also, the organelles are capable of self-replication through cellular division and can synthesize some of the constituent proteins that comprise their structure.

The mitochondrial network in the culture of MDOK epithelial cells presented in the digital image above was labeled with MitoTracker Red CMXRos, a derivative of X-rosamine. In addition, the cells were stained with Alexa Fluor 488 conjugated to phalloidin and Hoechst 33258, targeting filamentous actin and nuclear DNA, respectively. Images were recorded in grayscale with a QImaging Retiga Fast-EXi camera system coupled to an Olympus BX-51 microscope equipped with bandpass emission fluorescence filter optical blocks provided by Omega Optical. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.