The Cell Nucleus

At the center of the cell, you'll find a large round structure. This is the nucleus. The nucleus controls and guides all cellular activities. As you get closer to the nucleus, you discover it is surrounded by a porous membrane. This nuclear membrane serves the same function for the nucleus as the cell membrane does for the cell. It controls what enters and exits the nucleus.

The eukaryotic cell nucleus. Visible in this diagram are the ribosome-studded double membranes of the nuclear envelope, the DNA (complexed as chromatin), and the nucleolus. Within the cell nucleus is a viscous liquid called nucleoplasm, similar to the cytoplasm found outside the nucleus. Image from Wikipedia.

As you enter the nucleus, you immediately become tangled in a mass of threadlike material called chromatin. You untangle yourself and discover that the mass of threads is actually the cell's chromosomes, long ribbons of genetic material that direct cell activities. The chromosomes, which occur as pairs, are made up of packets of information called genes. The genes are actually segments of a complex molecule called deoxyribonucleic acid, or DNA for short. DNA holds the specific instructions that direct all cell processes.

In the nucleus you also see a spherical structure called the nucleolus. This structure manufactures ribosomes. Once a ribosome is manufactured in the nucleolus, it migrates out of the nucleus into the cytoplasm.

The directions contained in the DNA must be able to get out to the ribosomes in the nucleus. This is accomplished by ribonucleic acid, or RNA. RNA works as a messenger that picks up directions from DNA and carries them out to the cytoplasm. Once the ribosomes receive the directions, they make the desired product. This protein might become part of an organelle; or it might be used to repair a broken membrane.