Question

Which one inhibits protein synthesis by binding to 50S ribosomes?
A) Tetracycline
B) Streptomycin
C) Erythromycin
D) Penicillin

Answer 1

Hint: This Antibiotic is derived from soil-borne bacteria and it is used to treat chest infections, skin infections like acne etc. It belongs to the Macrolide group of Antibiotics.

Complete Answer:
- The question is about Antibiotics. Antibiotics are used to treat bacterial infections. When any Antibiotic comes in contact with the bacterial cells, these Antibiotics affect the protein synthesis and thus the cell dies.
- The Antibiotic attaches with the ribosomal unit (smaller or larger) and thus prevents the synthesis of protein which in turn prevents the growth and multiplication.
- Every Antibiotic has a different mechanism of action.
- Tetracycline and Streptomycin attach to the 30S (smaller unit) unit of prokaryotic ribosomes while Erythromycin binds to the 50S unit (larger unit). Penicillin affects bacterial cell wall formation and hence does not attach with any ribosomes.

Hence here the answer is option C.

Additional information: Ribosomes are tiny granular structures present in the living cells
- These structures help in protein synthesis
- Palade studied these structures for the first time and hence ribosomes are also known as ‘Palade particles’.
- Ribosomes are not bounded by any membrane.
- These structures consist of two subunits: larger and smaller subunits.
- Prokaryotic Ribosomes are 70S ribosomes and Eukaryotic ribosomes are 80S ribosomes
S is the Svedberg unit or Sedimentation coefficient.
- The value of S depends upon its centrifugation property.
- If any particle travels faster, the centrifugation unit will be higher.

Prokaryotic Ribosomes: This is made up of two units. The smaller unit is 30S unit and larger unit is 50S unit.
Eukaryotic Ribosomes: The larger unit is 60S and smaller unit is 40S

Note:
- During centrifugation, in prokaryotes if the smaller unit is centrifuged then the value is 30S and when larger unit is centrifuged the value is 50S. However when the intact unit is centrifuged the value is 70S.
- Similarly, in Eukaryotes the smaller unit centrifuged gives a value of 60S and the larger gives the value of 40S while the intact unit gives a value of 80S.