Ribosomes

Ribosomes are cellular structures responsible for translating genetic information from mRNA into functional proteins. Ribosomes are made up of ribosomal RNA (rRNA) and proteins. They are the site of protein synthesis. The ribosome structure consists of two subunits, a small subunit and a large subunit, each composed of ribosomal RNA (rRNA) molecules and proteins. In this article, we will cover ribosomes class 11 notes, the different types of ribosomes and their function.

Ribosome

Ribosomes are the site of protein synthesis in the cell. Ribosomes are granular structures and were first observed by George Palade (1953) under the electron microscope.

• A ribosome is present inside the living cells that produce proteins from amino acids during a process of protein synthesis also called translation, and it translates genetic information stored in messenger RNA into proteins. 
• Ribosomes are specialized cell organelles and are found in both prokaryotic and eukaryotic cells. 
• Ribosomes are found inside the cytosol of the cell.
• Ribosomes are composed of two subunits – smaller and larger.
• The mRNA binds and is decoded in the smaller subunit and the amino acids get added in the larger subunit. Both the subunits contain protein and ribonucleic acid components.
• These subunits are joined to each other by the interactions between proteins in one subunit and rRNAs in the other subunit.

The word ribosome is made from taking ‘ribo’ from ribonucleic acid and ‘soma’ is the Latin word for body.  

Function of Ribosomes

Ribosomes produce proteins from amino acids during a process called translation. It translates genetic information stored in messenger RNA into proteins. 

• The DNA produces mRNA by the process of DNA transcription.
• The mRNA is synthesized in the nucleus and transported to the cytoplasm for the process of protein synthesis.
• The ribosomal subunits in the cytoplasm are bound around mRNA polymers. 
• The tRNA synthesizes proteins.
• The proteins synthesized in the cytoplasm are utilized in the cytoplasm itself and the proteins synthesized by bound ribosomes are transported outside the cell.

Types of Ribosomes

The ribosomes present in eukaryotic cell is 80S whereas in prokaryotic cell 70S ribosomes are found. The ‘S’ (Svedberg’s Unit) here stand for sedimentation coefficient. It is indirectly used as a measure of density and size. The 70S and 80S are both made up of two subunits.

70S Ribosomes	80S Ribosomes
These are found both in prokaryotes and eukaryotes.	They occur in eukaryotic cells.
They are found freely inside the cytoplasm of prokaryotes and matrix of plastids and mitochondria of eukaryotes.	They are found inside the cytoplasm of eukaryotes either freely or attached to ER.
The sedimentation coefficient is 70.	The sedimentation coefficient is 80.
They are comparatively smaller in the length of (200—290 A) and diameter of (170— 210 A).	They are larger in the length of (300—340 A) and breadth (200—240 A).
They are lighter, 2.7—3.0 million Daltons.	They are heavier, 4.0—4.5 million Daltons.
The two subunits are the 30S and 50S.	The two subunits are the 40S and 60S.
They are synthesized in the cytoplasm of prokaryotes and matrix of semi-autonomous cell organelles.	They are synthesized inside the nucleolus.
It contains about 55 protein molecules, 34 in the larger subunit and 21 in the smaller subunit.	It contains about 73 protein molecules, 40 in the larger subunit and 33 in the smaller subunit.
The ribosomes contain more rRNA than protein (60:40).	The ribosomes possess less rRNA as compared to protein (40: 60).

Conclusion – Ribosome

In conclusion, ribosomes are cellular organelles which are responsible for protein synthesis. The 70S and 80S ribosomes exhibit distinct characteristics and functions in both prokaryotic and eukaryotic cells. They have differences in size, location, sedimentation coefficients, subunit composition, synthesis sites, and molecular composition. While 70S ribosomes are smaller, lighter, and occur freely in the cytoplasm or organelles, 80S ribosomes are larger, heavier, and may be attached to the endoplasmic reticulum in eukaryotes. Understanding these differences enhances our comprehension of protein synthesis processes and cellular functions across various organisms.

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FAQs on Ribosome

What are Ribosomes?

Ribosomes are cellular structures responsible for protein synthesis in all organisms.

What is the Role of Ribosomes?

Ribosomes assemble amino acids to form proteins that are essential to carry out cellular functions such as damage repair and other chemical processes.

How are Prokaryotic Ribosomes Different from Eukaryotic Ribosomes?

Prokaryotic ribosomes are smaller (70S), occur freely in the cytoplasm, and have fewer proteins, while eukaryotic ribosomes (80S) are larger, may be attached to the endoplasmic reticulum, and have more proteins.

Name Two Subunits of 70S Ribosomes.

The two subunits are the 30S and 50S.

Where are the 70S Ribosomes Synthesized?

70S ribosomes are synthesized in the cytoplasm of prokaryotic cells and the matrix of semi-autonomous organelles like mitochondria and plastids in eukaryotic cells.

Where is the Ribosome Located in a Cell?

Ribosomes are located either freely in the cytoplasm of prokaryotic cells or in the cytoplasm or attached to the endoplasmic reticulum in eukaryotic cells.

What are the Components of Ribosomes?

Ribosomes consist of two subunits made of ribosomal RNA (rRNA) and proteins.