Key Differences in Structure and Function of 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 Difference Between 70S and 80S Ribosomes in Prokaryotic and Eukaryotic Cells
1. What is the difference between 70S and 80S ribosomes?
The main difference between 70S and 80S ribosomes is their size, subunit composition, and location in cells. 70S ribosomes are smaller and found in prokaryotes, while 80S ribosomes are larger and found in eukaryotes.
- 70S ribosome = 50S large subunit + 30S small subunit
- 80S ribosome = 60S large subunit + 40S small subunit
- 70S occurs in bacteria and in mitochondria and chloroplasts
- 80S occurs in the cytoplasm of plant, animal, and fungal cells
2. What does the S in 70S and 80S ribosomes stand for?
The “S” in 70S and 80S ribosomes stands for Svedberg unit, a measure of sedimentation rate during ultracentrifugation. It reflects how fast a particle settles in a centrifugal field.
- It depends on size, shape, and density
- It is not directly additive (50S + 30S ≠ 80S)
- Higher S value means faster sedimentation
3. Where are 70S and 80S ribosomes found in the cell?
70S ribosomes are found in prokaryotic cells and in certain organelles of eukaryotes, while 80S ribosomes are found in the cytoplasm of eukaryotic cells.
- 70S ribosomes: Present in bacteria, mitochondria, and chloroplasts
- 80S ribosomes: Present in the cytosol and attached to rough endoplasmic reticulum in plants, animals, and fungi
4. What are the subunits of 70S and 80S ribosomes?
The 70S ribosome consists of 50S and 30S subunits, while the 80S ribosome consists of 60S and 40S subunits.
- 70S ribosome:
- Large subunit: 50S
- Small subunit: 30S
- 80S ribosome:
- Large subunit: 60S
- Small subunit: 40S
5. Why are 70S ribosomes smaller than 80S ribosomes?
70S ribosomes are smaller because they contain fewer rRNA molecules and proteins compared to 80S ribosomes.
- Prokaryotic ribosomes (70S) have simpler structure
- Eukaryotic ribosomes (80S) contain more rRNA types and additional proteins
- Eukaryotic cells are more complex, requiring more elaborate translation machinery
6. What is the function of 70S and 80S ribosomes?
Both 70S and 80S ribosomes function in protein synthesis by translating mRNA into polypeptide chains.
- Bind to messenger RNA (mRNA)
- Recruit transfer RNA (tRNA)
- Catalyze peptide bond formation
7. How do 70S and 80S ribosomes differ in rRNA composition?
70S and 80S ribosomes differ in the number and type of ribosomal RNA (rRNA) molecules they contain.
- 70S ribosome: Contains 23S rRNA and 5S rRNA in the 50S subunit, and 16S rRNA in the 30S subunit
- 80S ribosome: Contains 28S rRNA, 5.8S rRNA, and 5S rRNA in the 60S subunit, and 18S rRNA in the 40S subunit
8. Why do antibiotics target 70S ribosomes?
Many antibiotics target 70S ribosomes because they are structurally different from 80S ribosomes in human cells.
- Drugs like tetracycline and streptomycin bind specifically to bacterial ribosomal subunits
- This blocks bacterial protein synthesis
- Human 80S ribosomes remain largely unaffected
9. Are 70S ribosomes present in eukaryotic cells?
Yes, 70S ribosomes are present in eukaryotic cells inside mitochondria and chloroplasts.
- Mitochondria contain 70S ribosomes for synthesizing some of their own proteins
- Chloroplasts in plants also contain 70S ribosomes
- The cytoplasm of eukaryotic cells contains 80S ribosomes
10. Do 70S and 80S ribosomes perform the same process?
Yes, both 70S and 80S ribosomes perform the same basic process of translation, converting genetic information into proteins.
- Initiation: Ribosome assembles on mRNA
- Elongation: Amino acids are added to the growing chain
- Termination: Polypeptide is released
