The Difference Between Nucleus and Nucleolus

The Nucleus Has a Membrane

• The nucleus is a membrane-bound organelle. The membrane, referred to as the nuclear envelope or nuclear membrane, is actually made of two membranes. Each membrane consists of a lipid bilayer, a double layer of fatty acids surrounding the nucleus, separating its contents from the cytoplasm. The nuclear envelope also has pores, openings in the membrane allowing substances to move into and out of the nucleus. The nucleolus does not have a membrane surrounding it. The nucleolus is actually a dense spherical structure within the nucleus and is only visible when the cell is not dividing.

Nucleus Houses DNA

• The nucleus contains deoxyribonucleic acid (DNA), a double-stranded molecule carrying genetic information called genes, which are inside of chromosomes. Genes determine DNA sequencing, a code for protein production. DNA can also make an exact copy of itself in a process called DNA replication. During cell division, each cell receives a copy of its genetic instructions.

rRNA is Made in the Nucleolus

• The nucleolus is responsible for ribosomal ribonucleic acid (rRNA) synthesis. Proteins from the cytoplasm are assembled with the rRNA. The assembled package, called ribosomal subunits, move out of the nucleus and into the cytoplasm. Once in the cytoplasm of the cell, ribosomal subunits become ribosomes, organelles that are the sites of protein synthesis.

The Nucleus Contains Chromatin

• Chromosomes are a combination of DNA, genes and protein. The DNA-protein complex, called chromatin, is found inside of the nucleus and can be seen during cell division with the aid of a microscope. Chromatin has the appearance of fibers or threads and has double the amount of protein found in DNA, according to the U.S. National Library of Medicine. The proteins, of which there are over a thousand types, play an important role in gene expression and DNA replication.