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How big is a Cell Nucleus?

7 micrometres!

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Cell Nucleus

The nucleus is the compartment inside a cell that holds its chromosomes, the threadlike structures of DNA and protein that carry its genetic information. Plant and animal cells have a nucleus. In the cells of mammals, including people, a typical nucleus is about 7 micrometers across. A micrometer is a millionth of a meter, or a thousandth of a millimeter.

Size

A nucleus is usually round or oval, and its size is its diameter. In mammal cells it is typically 5–10 micrometers across. The explorer shows 7 micrometers, the figure one review uses for a typical mammal nucleus.

A human fibroblast, a cell type found in skin, has a nucleus about 10 micrometers across. The nucleus of a yeast cell is only about 2 micrometers across, while egg cells can have much larger ones.

How much of a cell the nucleus fills depends on the kind of cell. In a resting lymphocyte, a type of white blood cell, the nucleus takes up almost the whole cell. In fat cells and in macrophages, immune cells that engulf microbes, it takes up a much smaller share.

Size comparisons

  • A red blood cell, 7–8 micrometers across, is about as wide as a typical nucleus, but a red blood cell has no nucleus of its own.
  • About 11–14 nuclei 7 micrometers across, lined up side by side, would span the width of a human hair, which is 80–100 micrometers wide.
  • The DNA in one human cell would stretch about 1.8 meters (6 feet) if it were unwound and laid end to end. That is about 260,000 times as long as a 7-micrometer nucleus is wide.
  • If a nucleus were enlarged to the width of a basketball, about 24 centimeters (9.4 inches), the DNA inside it would stretch about 63 kilometers (39 miles).

What is inside

The nucleus is wrapped in the nuclear membrane, a double layer that separates the chromosomes from the rest of the cell. Holes called nuclear pores pass through it and let only certain molecules, such as proteins and RNA, in and out. In a yeast cell, the pores cover about a tenth of the inner surface of the membrane.

Inside, DNA is wound around spool-like proteins called histones, which is how so much of it fits. A round region called the nucleolus builds ribosomes, the machines that make proteins. The instructions for making a protein leave the nucleus as messenger RNA, a copy of a gene. Drifting at random, a messenger RNA takes an estimated 2–6 minutes to cross a typical 7-micrometer nucleus.

Cells without a nucleus

Living cells fall into two groups: eukaryotes, which have a nucleus, and prokaryotes, which do not. Some human cells have none either. Red blood cells and platelets, the cell fragments that help blood clot, have no nucleus. They are so numerous that a 2016 study estimated that almost 90 percent of the cells in the human body have no nucleus, while about 3 trillion do.

Before a cell divides, it copies its chromosomes and sorts them into two identical sets, one for each of two new nuclei. While this happens the old nucleus dissolves, and the chromosomes can be seen through a microscope.

Sources

Scale of the Universe > Cell Nucleus
Chloroplast
Plants use chloroplasts to turn the Sun's energy into chemical energy, which is stored in glucose molecules! Chloroplasts are also what give plants their green color, because they have fabulous chlorophyll inside their thylakoid membranes.
X Chromosome
X chromosomes are absolutely wonderful. Most chromosomes look like X's even if they aren't sex chromosomes – those are autosomes. In humans, females have two X chromosomes while males have an X and a Y chromosome. Some people might have three, four, or even five chromosomes, though.
E. coli
E. coli are usually harmless and live in your intestines, making wonderful vitamin K2. They are in almost everyone's intestines. In fact, they colonize babies' intestines just two days after they are born! Now that's pretty fast!
White Blood Cell
These mass murderers are also known as leukocytes. There are many different types of this disease-fighting cell. The most common type, the neutrophil, has multiple nuclei. The largest type, the macrophage, has a diameter of a whopping 21 µm.
Mist Droplet
Mist can reduce visibility a bit. It can also reflect light, so that you can see rays of light shining through it. That's pretty cool. If you want to find mist, go to the coast or the mountains. Mist is more common there.
Infrared Wavelength
Things that are extremely rare are "inf-rare". (infinitely rare). Inf-rare is also a verb, meaning "to make inf-rare". (e.g., "John inf-rared the precious food by eating the last of it.") Infrared light used to be quite common, but one day, a scientist somehow "infrared" it.

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