Energy on Demand

What am I looking at?

This video of a cell from a monkey’s kidney shows the dynamic network of endoplasmic reticulum (ER) tubules present in every eukaryotic cell, as well as mitochondria migrating around the cell’s interior. The ER is orange, and the mitochondria are blue.

Biology in the background

The ER is the protein synthesis and processing center of a cell. There are two types of ER in a cell: rough ER and smooth ER. The rough ER membrane is studded with ribosomes, which are molecular machines that synthesize proteins. The smooth ER is where some lipids, phospholipids, and steroids are synthesized and some protein folding and processing occur.

Mitochondria use a process called the Krebs cycle to generate energy for a cell. The Krebs cycle turns compounds from ingested carbohydrates into energy-rich molecules that other cellular processes can use for fuel. This energy is often stored for a limited time in a molecule called adenosine triphosphate (ATP), until it is needed for other cellular processes.

This process of protein synthesis is costly; adding a single amino acid to a peptide chain consumes four or five ATP molecules. But mitochondria can be transported along a cell’s cytoskeleton to any area of the cell that has high ATP requirements, such as the most active regions of the ER, matching energy demand and supply. You can think of it as the power plants of the cell using cellular highways to reach the protein factory.

The mitochondria in a human cell range from 0.5 micrometer to 1 micrometer in diameter, or roughly 150 to 75 times smaller than the width of a human hair, while an ER tubule can range in size from 50 to 100 nanometers, or roughly 1,500 to 750 times smaller than the width of a human hair.

Technique

This video was created using confocal microscopy.