What is the Difference Between 70S and 80S Ribosomes

The main difference between 70S and 80S ribosomes is that 70S ribosomes occur in prokaryotes, whereas 80S ribosomes occur in eukaryotes.

The 70S and 80S ribosomes are the two ribosome types that occur in organisms. Their function is to translate mRNA into proteins.  

Key Areas Covered

1. What is a Ribosome
– Definition, Features, Function
2. What is 70S Ribosome
– Definition, Features, Function
3. What is 80S Ribosome
– Definition, Features, Function
4. Similarities Between 70S and 80S Ribosomes
– Outline of Common Features
5. Difference Between 70S and 80S Ribosomes
– Comparison of Key Differences

Key Terms  

70S Ribosome, 80S Ribosome, Ribosome

What is a Ribosome

A ribosome is a molecular machine in prokaryotic and eukaryotic cells that facilitates linking amino acid precursors in an order specified by the messenger RNA (mRNA). The major function of ribosomes is protein synthesis. Ribosomes are composed of two unequal subunits called the small and large subunits. The small subunit reads the mRNA, while the large subunit facilitates linking the precursor amino acids into a polypeptide chain. The process is referred to as translation.

Furthermore, ribosomes occur free or membrane-bound. Some eukaryotic ribosomes are bound to the rough ER, while the other ribosome types freely move in the cytosol. Membrane-bound ribosomes import the synthesized polypeptide chain into rough ER to achieve further modifications and protein folding into the 3-D structure. Proteins are required by the cell for various functions, such as directing chemical processes, repairing damage, and cell signaling.

What is a 70S Ribosome?

70S ribosomes occur in prokaryotes. These prokaryotic ribosomes are the small ribosomes involved in translation, mainly in bacteria and archaea. Also, mitochondria and chloroplasts in the eukaryotic cells contain 70S ribosomes since these organelles evolved from endosymbiosis.

Figure 1: 70S Ribosome

Further, the large subunit of the prokaryotic ribosomes is 50S, while the small subunit is 30S.

What is an 80S Ribosomes?

80S ribosomes occur in eukaryotes. Eukaryotic ribosomes are the large ribosomes that only occur in eukaryotic cells such as animals, plants, fungi, and other unicellular, eukaryotic organisms. Their large subunit is 60S, and the small subunit is 40S.

Figure 2: 80S Ribosome

Most eukaryotic ribosomes are membrane-bound, but some are free in the cytoplasm. The main function of a ribosome is to serve as a site for protein synthesis by facilitating the linkage of amino acids in an order specified by the mRNA. This process is known as translation. Moreover, ribosomes are also called translational apparatus.

Similarities Between 70S and 80S Ribosomes

• The 70S and 80S ribosomes are two ribosome types that occur in organisms.
• They translate mRNA into proteins.
• Also, they are made up of two subunits called small and large subunits.
• Besides, they both are made up of rRNA. 

Difference Between 70S and 80S Ribosomes

Definition

70S ribosomes refer to the prokaryotic ribosomes, while 80S ribosomes refer to the eukaryotic ribosomes. 

Size

70S ribosomes are small, while 80S ribosomes are small. The mass of 70S ribosomes is 27000 kd, while the mass of 80S ribosomes is 42000 kd. Also, the diameter of 70S ribosomes is ~200 Å while the diameter of 80S ribosomes is ~250-300 Å.

Subunits

70S ribosomes are made up of 50S and 30S subunits while 80S ribosomes are made up of 60S and 40S subunits.

Large Subunit

The large subunit of 70S ribosomes is made up of two rRNA molecules, 23S rRNA and 5S rRNA, while the large subunit of eukaryotic ribosomes is made up of three rRNA molecules, 28S rRNA, 5.3S rRNA, and 5S rRNA.

Small Subunit

The small subunit of 70S ribosomes is made up of 16S rRNA, while the small subunit of 80S ribosomes is made up of 18S rRNA.

Ribosomal Protein Ratio

The 70S ribosomes are made up of 60% rRNA and 40% ribosomal proteins, while the 80S ribosomes are made up of 40% rRNA and 60% ribosomal proteins. 

Location

The 70S ribosomes occur free in the cytosol of prokaryotes and inside the chloroplasts and mitochondria of eukaryotes, while the 80S ribosomes occur either free or attached to the ER.

Conclusion

In brief, 70s and 80S ribosomes are two ribosome types in organisms. Their function is to translate mRNA into proteins. The 70S ribosomes occur in prokaryotes and inside eukaryotic chloroplasts and mitochondria. Also, they contain 50S and 30S subunits. In comparison, 80S ribosomes occur free or bound to ER inside the eukaryotic cells. They contain 60S and 40S subunits. Therefore, the main difference between 70S and 80S ribosomes is their location. 

References:

1. Ribosome. Genome.gov. (n.d.-c). https://www.genome.gov/genetics-glossary/Ribosome#:~:text=A%20ribosome%20is%20an%20intercellular,that%20fold%20to%20form%20proteins.

Image Courtesy:

1. “OSC Microbio 03 03 Ribosome ” By CNX OpenStax – Own Work (CC-BY 4.0) via Commons Wikimedia
2. “80S 2XZM 4A17 4A19” By Fvoigtsh – Own work (CC-BY SA 3.0) via Commons Wikimedia