Ribosomes are important parts of cells. They help make proteins, which are essential for all living things. While ribosomes in eukaryotic (complex) and prokaryotic (simple) cells do the same job, they are built and work a little differently.

What Are Ribosomes Made Of?

1. Composition:

   • Ribosomes are made of ribosomal RNA (rRNA) and proteins.
   • Eukaryotic ribosomes are bigger. They are called 80S ribosomes and have two parts: a 60S large subunit and a 40S small subunit.
   • Prokaryotic ribosomes are smaller, called 70S. They consist of a 50S large subunit and a 30S small subunit.

2. Size Comparison:

   • Eukaryotic ribosomes: 80S
   • Prokaryotic ribosomes: 70S

Where Are Ribosomes Found?

• Eukaryotic Cells:
  • In these cells, ribosomes can be floating freely in the cytosol (the jelly-like part of the cell) or attached to the endoplasmic reticulum (ER), which is called rough ER.
  • About 30% of ribosomes in a eukaryotic cell are attached to the rough ER.
• Prokaryotic Cells:
  • Ribosomes are only found in the cytoplasm because prokaryotic cells don’t have membrane-bound organelles.

How Do Ribosomes Make Proteins?

1. Starting the Process:

   • In prokaryotes, ribosomal RNA attaches to a special part of the mRNA called the Shine-Dalgarno sequence. This helps place the ribosome in the right spot to start making protein.
   • In eukaryotes, the ribosome finds the 5' cap of the mRNA and scans for the start signal (AUG).

2. Building the Protein:

   • After starting, tRNA brings amino acids to the ribosome in both cell types.
   • The ribosome helps link these amino acids together.
   • Prokaryotes make proteins faster, at about 20 amino acids per second, while eukaryotes make them at about 5 amino acids per second.

3. Ending the Process:

   • The ribosome reaches a stop signal and releases the finished protein.
   • Both types of cells use special release factors to finish this step, but the proteins and methods they use are different.

Different Functions of Ribosomes

• Polyribosomes:
  • Both eukaryotic and prokaryotic cells can have polyribosomes, which means several ribosomes can work on one piece of mRNA at the same time.
  • This makes protein production more efficient and helps cells react faster to their needs.

Unique Features of Ribosomes

• Antibiotic Sensitivity:

  • Prokaryotic ribosomes are affected by many antibiotics (like tetracycline and streptomycin), which can block the activity of bacterial ribosomes without harming eukaryotic ribosomes. This shows the differences between the two cell types.

• Where Are Ribosomes Made?:

  • In eukaryotic cells, ribosomes are made in a part called the nucleolus. In prokaryotic cells, they are made freely in the cytoplasm.

In Summary

Both eukaryotic and prokaryotic ribosomes play a key role in making proteins. However, they differ in size, structure, location, and how efficiently they work. Understanding these differences helps us learn more about how cells function and how living things work.