Question

Starting with shredded spinach leaves, you follow a procedure that allows for separation of cellular organelles. You are specifically looking for the fraction that contains the mitochondria. To identify this fraction, you should test for the

Answer 1

Cellular organelles are separated by the process of centrifugation. By using differential centrifugation at low speed, we can remove the pellet containing organelles like the intact plastids, cell wall membranes, nuclei and starch grains. This is followed by a faster centrifugation of the left supernatant that further forms the pellet containing crude mitochondria. This pellet contains intact and damaged mitochondria, plastids and peroxisomes. The supernatant is discarded. The intact mitochondria is then separated from the rest of the pellet by density gradient centrifugation. At the end of this method, the intact mitochondria separates from the rest of the pellet as it is seen at the top of the wash medium. It forms a distinct band, well away from the contaminants. So, to identify the fraction that contains intact mitochondria we must test for the density of mitochondria by using density gradient centrifugation.