Objective: UPlanSApo 100x oil/1.40	Exposure: 200 ms
Microscope: Olympus DSU/IX81	Gain: 3
Camera: Hamamatsu ImagEM	Interval: 1 s

Depending upon the metabolic requirements of an organism, a cell can contain between one and many thousands of mitochondria. First discovered through the use of a light microscope in the 1800s, these large organelles are found in almost all eukaryotes: animals, protists, and even fungi. The scientists who first observed these organelles, because of the way they appeared under the microscope, termed them mitochondria after the Greek words for “granule” and “thread”. Before the mid-1950s, it was believed that mitochondria transmitted hereditary information when, finally, a method of isolating the organelles without damaging them was developed. This break-through led to our current understanding of the functioning of the mitochondrion. In the digital video presented in this section, a human osteosarcoma cell (U2OS line) is co-expressing DsRed fluorescent protein fused to an endoplasmic reticulum targeting signal and mEGFP fused to a mitochondria targeting signal.