MEMPHIS, Aug. 2 (UPI) -- U.S. scientists say they've found the key event in cell death occurs as single, quick event and not a step-by-step process as previously believed. The researchers at St. Jude Children's Research Hospital in Memphis, Tenn., determined apoptosis, or 'cell suicide,' eliminates extraneous cells from the developing body and disposes of cells that sustain irreparable harm to their DNA or are infected with microorganisms. The researchers photographed individual cells undergoing that process, allowing investigators to observe the release of certain proteins from pores in the membranes of mitochondria. The cellular structures contain enzymes that extract energy from food molecules, and the space within the membrane surrounding them holds a variety of proteins that are released during apoptosis. Results of the study indicate the formation of pores in the mitochondrial membranes is a rapid process that allows a nearly simultaneous, rather than a sequential, release of many apoptosis proteins, according to Douglas Green, chairman of the St. Jude Department of Immunology and senior author of the study. The research appears in the Proceedings of the National Academy of Sciences.