Do Eukaryotic Cells Have Ribosomes? 9 Facts You should Know


The cells of all the living organisms have ribosomes, popularly known as non-membranous organelles. These cell organelles are located on the rough endoplasmic reticulum.

The cells of all the eukaryotic organisms have ribosomes. The site for protein synthesis is the ribosome where the translation of genetic information takes place. Here we will know the 9 facts about do eukaryotic cells have ribosomes

  • In eukaryotic cells, 80S ribosomes are identified.
  • Ribosomes play a significant role in protein synthesis.
  • Ribosomes can be free-living or membrane-bound.
  • All living organisms are known to have ribosomes.
  • Ribosome was discovered by George Palade.
  • Eukaryotic ribosomes are made up of ribosomal RNA and ribosomal proteins.
  • The term ‘rough’ endoplasmic reticulum was coined due to the presence of ribosomes in the endoplasmic reticulum.
  • Ribosomes along with their components are known as translational apparatus due to their ability to translate genetic information coded in DNA into proteins.
  • Unlike other cell organelles, ribosomes are not membrane-bound structures.

Do all eukaryotic cells have ribosomes?

Yes, the cells of all the eukaryotic organisms have ribosomes. Apart from the mature red blood cells, all the cells in a eukaryotic organism have ribosomes.

Do eukaryotic cells have free ribosomes?

Yes, eukaryotic cells have free ribosomes. Free ribosomes and membrane-bound are the two types of ribosomes found in eukaryotic cells. Free ribosomes can move around freely throughout the cytoplasm of a cell. These are also known as cytoplasmic ribosomes.

However, several ribosomes are found attached to the endoplasmic reticulum and are unable to move around the cell. These types of ribosomes are called attached ribosomes. Membrane-bound ribosomes include mitoribosomes present in mitochondria and plastoribosomes present in chloroplasts.

Do eukaryotic cells have 80S ribosomes?

Yes, eukaryotic cells have 80S ribosomes. All living organisms are reported to have ribosomes that help in catalyzing protein synthesis.

Two types of ribosomes are identified across various organisms viz; 80S and 70S; ‘S’ is a Svedberg unit indicating sedimentation coefficient. 80S ribosomes present in eukaryotic cells are a combination of a small subunit, 40S, and a large subunit, 60S.

do eukaryotic cells have ribosomes
Structure of ribosome from Wikimedia

Do eukaryotic cells have 70S ribosomes?

No, eukaryotic cells do not have 70S ribosomes. 70S ribosomes are present in prokaryotic cells. Like eukaryotic ribosome 80S, 70S ribosome is also an aggregation of two subunits; a small subunit 30S and a large subunit 50S.

Do eukaryotic cells have small ribosomes?

The ribosomes identified in the eukaryotic cells are larger in size in comparison to the prokaryotic cells. The size of eukaryotic ribosomes ranges from 25 – 30 nm in diameter, whereas prokaryotic ribosomes are around 20 nm in diameter.

Where are ribosomes in eukaryotic cells?

Ribosomes are either attached to the rough endoplasmic reticulum or found floating freely in the cytoplasm. The location of the ribosome depends on the presence of an endoplasmic reticulum-specific signal sequence on the protein synthesized by the ribosome. The proteins used within the cell are produced by the free ribosomes.

The proteins synthesized for the functioning of different cell organelles are produced by the ribosomes attached to the rough endoplasmic reticulum. These proteins are either used by cell organelles or secreted out of the cell via exocytosis.

Eukaryotic cell ribosome size.

The ribosome in a eukaryotic cell is known as the 80S ribosome, where ‘S’ is the sedimentation coefficient. Eukaryotic ribosomes consist of 50 % ribosomal RNA and 50 % ribosomal protein, whereas prokaryotic ribosomes consist of 65 % ribosomal RNA and 35 % ribosomal protein.

Eukaryotic cell ribosome’s function.

In eukaryotic cells, ribosomes act as protein-synthesizing machines. The ribosomal proteins act as scaffolds that enhance the catalytic ability of ribosomal RNA to synthesize protein.

The two essential functions of ribosomes are: decoding genetic information and forming a peptide bond. Genetic information is interpreted by 40S, the small subunit, and peptide bonds are formed by 60S, the large subunit. Ribosomes translate genetic information from mRNA to proteins using mRNA as a template.

mRNA consists of a series of codons that have complementary anticodon on aminoacyl tRNA, which plays a crucial role in protein synthesis. Apart from anticodon, aminoacyl tRNA also consists of specific amino acids. The amino acids placed next to each other as per the mRNA template lead to a polypeptide chain which is the primary structure of a protein.

Eukaryotic cell ribosome’s structure.

In eukaryotic cells, a ribosome is present as an aggregation of two subunits, i.e.; 40S and 60S. These two subunits are combinedly referred to as 80S ribosomes.

Further, the 40S subunit consists of 33 proteins and 18S RNA and the 60S subunit is composed of 46 proteins, 28S RNA, 5.8S RNA, and 5S RNA. The atomic structure of the 80S eukaryotic ribosome was derived for the first time from the yeast Saccharomyces cerevisiae.

Summary

Altogether, eukaryotic ribosomes catalyze protein synthesis with the help of ribosomal RNA. Ribosomes are essential for the synthesis of proteins in a eukaryotic cell.

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