Category: Cells

A cross-section of a cell showing organelles. Credit: Judith Stoffer.

Welcome to our tour of the cell! Imagine you’ve shrunk down to about 3 millionths of your normal size. You are now about 0.5 micrometers tall (a micrometer is 1/1,000th of a millimeter). At this scale, a medium-sized human cell looks as long, high, and wide as a football field. But you can’t see nearly that far. Clogging your view is a rich stew of molecules, fibers, and various cell structures called organelles. Like the internal organs in your body, organelles in the cell each have a unique biological role to play.

The Nucleus and Its Closest Neighbor

Our first stop is the somewhat spherical structure about 50 feet in diameter. It’s the nucleus—basically the cell’s brain. The nucleus is the most prominent organelle and can occupy up to 10 percent of the space inside a cell. It contains the equivalent of the cell’s genetic material, or DNA.

Mitochondria (purple) in a rodent heart muscle cell. Credit: Thomas Deerinck, National Center for Microscopy and Imaging Research.

Mitochondria (mitochondrion in singular) are indispensable. Every cell of our bodies, apart from mature red blood cells, contains the capsule-shaped organelles that generate more than 90 percent of our energy, which is why they’re often called “the powerhouse of the cell.” They produce this energy by forming adenosine triphosphate (ATP), our cells’ most common energy source. But mitochondria also support cells in other ways. For example, they help cells maintain the correct concentration of calcium ions, which are involved in blood clotting and muscle contraction. Mitochondria are also the only structure in our cells with their own unique DNA, which with rare exceptions, is inherited only from mothers. That’s why, in honor of Mother’s Day, we’re exploring this special cellular connection to moms.