Ribosomes are classified according to their:
- The sedimentation rate or sedimentation coefficient (expressed in Svedberg units, S) is an essential attribute used to classify ribosomes.
- It reflects how quickly ribosomes settle under the force of gravity in a centrifuge.
- Prokaryotic ribosomes, being smaller, sediment faster and have lower S values (around 70S).
- Eukaryotic ribosomes, being larger, sediment more slowly and have higher S values (approximately 80S).
- This sedimentation rate classification aids in distinguishing ribosomes between different types of cells and organisms.
Classification on basis of location:
Ribosomes are classified based on their location and mode of synthesis. There are two main types of ribosomes: free ribosomes and membrane-bound ribosomes, also known as the rough endoplasmic reticulum (ER) ribosomes.
1. Free ribosomes:
- These ribosomes are suspended freely in the cytoplasm of the cell.
- They are responsible for synthesizing proteins that are required within the cytoplasm itself or for proteins destined for other organelles within the cell.
- Free ribosomes mainly produce proteins involved in cellular metabolism and function.
2. Membrane-bound ribosomes (rough ER ribosomes):
- These ribosomes are attached to the endoplasmic reticulum (ER), giving it a rough appearance under a microscope.
- Ribosomes attached to the rough ER are involved in synthesizing proteins that are to be exported outside of the cell, incorporated into the cell membrane, or transported to various cellular compartments such as the Golgi apparatus.
- These proteins play crucial roles in cell signaling, membrane structure, and secretion.
