Structure and Function: Comparing 70S and 80S Ribosomes
Ribosomes are the particles present in the cells in large numbers and mainly serve as a site for protein synthesis. They are present as free particles in both prokaryotic and eukaryotic cells and also attached to the membrane of the endoplasmic reticulum in the case of eukaryotic cells. The discovery of ribosomes was in the year 1955 by a Romanian-American cell biologist George E. Palade; during his discovery, he found that ribosomes are associated with the endoplasmic reticulum in eukaryotic cells.
Along with protein synthesis, they also function by binding to a messenger ribonucleic acid (mRNA) and decoding the information carried by the nucleotide sequence of the mRNA. The transfer RNA’s having amino acids enters into the ribosomes at the acceptor site. Once after getting added up, it further adds amino acids to the growing protein chain on tRNA.
Difference Between the 70S and 80S Ribosomes
FAQs on 70S vs 80S Ribosomes: What Sets Them Apart?
1. What is the main difference between 70S and 80S ribosomes?
The main difference between 70S and 80S ribosomes lies in their sedimentation coefficient ('S'), size, location, and composition. 70S ribosomes are smaller and found in prokaryotes (like bacteria) and in the mitochondria and chloroplasts of eukaryotes. 80S ribosomes are larger and are found in the cytoplasm of eukaryotic cells (like in plants and animals). Their subunits and RNA content also differ significantly.
2. What are the subunits that make up 70S and 80S ribosomes?
Each type of ribosome is composed of two distinct subunits, a large and a small one:
70S ribosomes consist of a smaller 30S subunit and a larger 50S subunit.
80S ribosomes consist of a smaller 40S subunit and a larger 60S subunit.
3. Where are 70S and 80S ribosomes typically found?
The location of these ribosomes is a key identifier of cell type:
70S ribosomes are found in the cytoplasm of prokaryotic cells (e.g., bacteria) and within the organelles of eukaryotic cells, specifically the mitochondria and chloroplasts.
80S ribosomes are found in the cytoplasm of eukaryotic cells, either free-floating or attached to the membrane of the endoplasmic reticulum.
4. What is the fundamental function of ribosomes in a cell?
The fundamental function of all ribosomes, both 70S and 80S, is protein synthesis. They act as the site for a process called translation, where the genetic code from messenger RNA (mRNA) is read, and a specific sequence of amino acids is linked together to form a polypeptide chain, which then folds into a functional protein.
5. What does the 'S' in 70S and 80S stand for, and why are the subunit values not additive?
The 'S' stands for Svedberg unit, which is a measure of the rate of sedimentation of a particle in a centrifuge, not its mass. The subunit values are not additive (e.g., 30S + 50S ≠ 80S) because the sedimentation rate depends on both mass and shape. When the two subunits combine, the overall shape is more compact, causing it to sediment at a rate different from the simple sum of its parts.
6. How does the difference between 70S and 80S ribosomes have medical importance?
This difference is crucial for the development of antibiotics. Many antibiotics, such as streptomycin and tetracycline, are designed to selectively target and inhibit the function of the 70S ribosomes found in bacteria. This stops the bacteria from producing essential proteins, leading to their death, without affecting the 80S ribosomes of the human host, thus treating the infection effectively.
7. Do human cells contain both 70S and 80S ribosomes?
Yes, human cells contain both types of ribosomes. The cytoplasm of human cells has 80S ribosomes for its own protein synthesis. However, human cells also have mitochondria, which are organelles responsible for energy production. These mitochondria contain their own 70S ribosomes, similar to those in prokaryotes. This is a key piece of evidence for the endosymbiotic theory of eukaryotic evolution.
