The key difference between prokaryotic and eukaryotic ribosomes is that the prokaryotic ribosomes are 70S particles composed of 50S large subunit and 30S small subunit while the eukaryotic ribosomes are 80S particles composed of 60S large subunit and a 40S small subunit.
Prokaryotes and eukaryotes are two major groups of living organisms that differ from the cellular organization. Prokaryotes do not possess a nucleus and membrane-bound cell organelles. On the other hand, eukaryotes possess a nucleus and membrane-bound cell organelles. There are some organelles common to both organisms. The ribosome is one of the important and vital organelles present in both prokaryotic and eukaryotic cells. They are present in the cytoplasm of each cell. Structurally, protein and ribosomal RNA (rRNA) together make up ribosomes. And they consist of two subunits namely larger subunit and a small subunit. Also, they carry out the same function that is the translation of mRNA molecules into proteins. Since translation is a vital process for all living organisms and it occurs in the ribosomes, ribosomes are very important for both prokaryotes and eukaryotes. Despite having many similarities, there are some differences between prokaryotic and eukaryotic ribosomes.
CONTENTS
1. Overview and Key Difference
2. What are Prokaryotic Ribosomes
3. What are Eukaryotic Ribosomes
4. Similarities Between Prokaryotic and Eukaryotic Ribosomes
5. Side by Side Comparison – Prokaryotic vs Eukaryotic Ribosomes in Tabular Form
6. Summary
What are Prokaryotic Ribosomes?
Prokaryotic ribosomes are 70S ribosomes, which are smaller than eukaryotic ribosomes. They consist of two subunits; small subunit and a large subunit. Small subunit of prokaryotic ribosomes is the 30S while the large subunit is 50S. These ribosomes units are denoted by Svedberg (S) values depending on the rate of the sedimentation in the centrifugation.
Figure 01: Prokaryotic Ribosomes
Moreover, in prokaryotes, rRNA is organized into three strands in ribosomes. Three strands are 16 S RNA, 5S RNA and 23S RNA. Unlike eukaryotic ribosomes, prokaryotic ribosomes do not attach with the membranes of the nucleus or endoplasmic reticulum. They are present freely in the cytoplasm.
What are Eukaryotic Ribosomes?
Eukaryotic ribosomes are 80S particles which are larger than prokaryotic ribosomes. They consist of 40S small subunit and 60S large subunit. Furthermore, eukaryotic ribosomes contain more ribosomal proteins than the prokaryotic ribosomes.
Figure 02: Eukaryotic Ribosomes
There are four strands of RNA in eukaryotic ribosomes. They are 18S, 5S, 5.8S and 28S RNAs. Unlike prokaryotic ribosomes, eukaryotic ribosomes are found freely in the cytoplasm and also attached to nuclear and ER membranes.
What are the Similarities Between Prokaryotic and Eukaryotic Ribosomes?
- Prokaryotic and eukaryotic ribosomes are components of the living cells.
- They provide a site for protein synthesis.
- Furthermore, they are made from RNA and ribosomal proteins.
- Also, they contain two subunits made up of RNAs.
- Moreover, both are present in the cytoplasm of the cell.
- Besides, their small subunit constituted with a single strand of RNA.
What is the Difference Between Prokaryotic and Eukaryotic Ribosomes?
Prokaryotic ribosomes are smaller 70S particles while the eukaryotic ribosomes are larger 80S particles. Therefore, this is the key difference between prokaryotic and eukaryotic ribosomes. Furthermore, another difference between prokaryotic and eukaryotic ribosomes is that the prokaryotic ribosomes consist of 30S and 50S, the smaller unit and the larger unit respectively whereas eukaryotic ribosomes have smaller subunit and larger subunit as 40S and 60S respectively. Moreover, in eukaryotes, rRNA in ribosomes has four strands whereas, in prokaryotes, rRNA is organized into three strands in ribosomes. Hence it is also a difference between prokaryotic and eukaryotic ribosomes.
Also, in eukaryotic cells, ribosomes are present as free and bound forms while in prokaryotic cells, ribosomes are present in the free form in the cytoplasm. Eukaryotic cells have chloroplasts and mitochondria as organelles, and those organelles also have ribosomes 70S. Therefore, eukaryotic cells have different types of ribosomes (70S and 80S), whereas prokaryotic cells only have 70S ribosomes. Eukaryotic ribosome consists of eight kinds of protein and four kinds of rRNA while the prokaryotic ribosomes consist of three types of rRNA and fifty kinds of protein. Therefore this is also a difference between prokaryotic and eukaryotic ribosomes.
Below is an infographic on the difference between prokaryotic and eukaryotic ribosomes that presents all these differences as a side by side comparison.
Summary – Prokaryotic vs Eukaryotic Ribosomes
The ribosome is the site of protein synthesis in living cells. However, prokaryotic and eukaryotic ribosomes differ from several features. Prokaryotic ribosomes are 70S particles composing of 30S and 50S subunits. On the other hand, eukaryotic ribosomes are 80S particles composing of 40S and 60S subunits. We can consider this as a key difference between prokaryotic and eukaryotic ribosomes. Furthermore, prokaryotic ribosomes contain three strands of RNA while eukaryotic ribosomes contain four strands of RNA. Prokaryotic ribosomes are present freely in the cytoplasm of the cell while the eukaryotic ribosomes are present in the cytoplasm freely as well as attached to nuclear and ER membranes. Thus, this summarizes the difference between prokaryotic and eukaryotic ribosomes.
Reference:
1. Nature News, Nature Publishing Group. Available here
2. Shaffer, Catherine. “Ribosome Structure.” News-Medical.net, News Medical, 23 Aug. 2018. Available here
Image Courtesy:
1.”Prokaryote cell diagram”By Mariana Ruiz LadyofHats – Own work (Public Domain) via Commons Wikimedia
2.”ProteinTranslation” (Public Domain) via Commons Wikimedia