We explain what ribosomes are, their history and how they were discovered. Their characteristics and stages of protein synthesis.
What are Ribosomes?
Ribosomes They are supramolecular complexes formed by nucleic acid (RNA molecules) and proteins. They are present in cells throughout the body (with the exception of sperm), although they are found in greater quantities in the cells of the liver and pancreas. They are part of the membrane of the endoplasmic reticulum.
Protein synthesis takes place within the ribosomes, that is, They are structures that generate proteins from genetic information. which is contained in DNA.
Ribosomes They use RNA as an intermediary to access DNA information. and thus produce proteins. Below, and as a summary, we explain what they are used for, and their main characteristics.
See also: Lysosomes.
History and discovery of ribosomes
Ribosomes They were first observed in the 1930s by Albert Claude who called them microsomesIt was not until the 1950s that George Palade observed these organelles using electron microscopy. These observations led to the suspicion that ribosomes were the site where protein synthesis took place, a hypothesis that was confirmed only in 1955 by Paul Zamecnik.
Origin of ribosomes
They originate in the center of the cell nucleus but then they travel to the cytoplasm, where they perform various functions depending on the cell to which they belong.
Ribosome size
The size of ribosomes is tiny, so they can only be observed through a microscope. This size It will depend on the cell in which it is located.In eukaryotic cells it will have a diameter of 320 ångström. In prokaryotes its size decreases to 290 ångström.
Number of ribosomes in a cell
The number of ribosomes found in each cell will largely depend on the purpose of the ribosomes, however it is estimated that Each cell can have several million ribosomes inside it..
Ribosome distribution
Ribosomes They can be found in isolation within the cell or they can form polyribosomes (groups of several ribosomes). They can also be attached to the endoplasmic reticulum or next to the cell membrane.
Structure of ribosomes
They are composed of two sub-units. Between both subunits is the protein chain and the RNA.These two subunits couple together during protein synthesis. Under the microscope they appear as dark, granular-looking structures.
- Small or minor structure
- Large or major structure
Participation of other components in protein synthesis
- Transfer RNA. This RNA is responsible for transporting amino acids.
- Messenger RNA. It transmits information of genetic origin to the ribosomes.
Stages of protein synthesis or translation
There are 3 stages:
- Initiation stage. During this stage, the messenger RNA arrives with the genetic information and is deposited in a small subunit. The transfer RNA transports the amino acids according to the information in the messenger RNA. Finally, both subunits couple together to form a complete ribosome.
- Stage of lengthening or elongation. Amino acids join together and form what is called polypeptideThis process is called protein synthesis.
- Completion stage. Messenger RNA completes its task of transmitting DNA and shortens the chain (polysome), releasing the finished protein.
Difference between ribosomes and polysomes
A polysome is a chain of ribosomes linked together by a 2 mm thick filament. The main function of ribosomes is the synthesis of export proteins (they will travel to other cells), while Polysomes synthesize cellular localization proteins.
Fate of proteins
Depending on their purpose, proteins can have different destinations. This It depends on the amount of peptides they haveA peptide is a type of molecule formed by the union of several amino acids.