What Is the Difference Between Ribosome & Ribosomal DNA?

By Don Jay Garrett
DNA, from which you transcribe mRNA, forms a double helix.
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Ribosomes are cell organelles that help produce new proteins within the cells. Ribosomal DNA (or rDNA) is the DNA segments that provide the gene code for the ribosomal RNA (or rRNA) that are made inside the cell nucleus. Ribosomal RNA molecules are the strucural components of the ribosome. Together, these molecules help the cell, and therefore the organism at large, produce new protein molecules that are required for all body processes such as cell growth, cell division, and adaptation. Proteins also form other important molecules such as enzymes, muscle proteins and structural proteins.


Ribosomes are small cellular organelles made of proteins and ribosomal RNA. A ribosome is composed of large and small globular subunits that fit together precisely. The junction of these two subunits is the site of protein synthesis, or the creation of new protein molecules. Some ribosomes float around freely within the cell cytoplasm while other ribosomes are attached to another cell organelle called an endoplasmic reticulum. When ribosomes are connected to the endoplasmic reticulum, it is then called a rough endoplasmic reticulum, or rough ER.

Ribosomal DNA

Ribosomal DNA provides the genetic coding from which rRNA molecules are constructed. As the DNA double helix unwinds, other RNA molecules read the template that is provided from this DNA sequence and an rRNA molecule is formed. Since these DNA segments do not provide the code for specific proteins, the rRNA products produced from these DNA genes are considered their end products. As a result, rRNA molecules produced by rDNA molecules are stable, long-lasting components of the ribosome.

Tandem rDNA Sequences

Ribosomal DNA is widely studied due to its often repeated segments within an organism's genome, or genetic structure. This property is called tandemly repeated DNA and helps to expand the size of an organism's genetic code to provide redundancy and adaptability. Tandem rDNA sequences are distinct in that they are placed next to each other in a genetic sequence. This pattern differs from other repeat sequences that are repeated randomly throughout the genetic sequence.

Protein Synthesis

Protein synthesis is a multi-step process that starts in the cell nucleus and ends in several of the cell's organelles. The ribosome is actively involved in protein synthesis. When a specific protein is required by a cell, the portion of DNA that codes for the protein uncoils and is read or transcribed in the nucleus, forming a messenger RNA (mRNA) molecule. The mRNA molecule exits the nucleus and goes to a ribosome in the cell cytoplasm. The ribosome interprets or translates the mRNA molecule and attaches the necessary protein building blocks to form the new protein molecule. The protein is then either modified or released to carry out the function it was created for.

About the Author

Don Jay Garrett is an anatomy and physiology instructor for nursing students. He also teaches CPR for local hospitals. Garrett holds a Master and a Bachelor of Science in exercise science. Previously, he was in the health and fitness field for more than 12 years, working as a fitness manager, exercise physiologist and personal trainer.