Mode of action of streptomycin:

Streptomycin is an antibiotic that belongs to the class of aminoglycosides. It was one of the first antibiotics discovered and is known for its broad-spectrum activity against various bacteria. Its mode of action involves the prevention of the formation of 70S ribosomes in bacteria.

1. Introduction to streptomycin:
- Streptomycin is derived from the soil bacterium Streptomyces griseus.
- It was first isolated in 1943 and is commonly used to treat infections caused by Gram-negative bacteria such as Mycobacterium tuberculosis, Escherichia coli, and many others.
- Streptomycin is a protein synthesis inhibitor and acts by binding to the 30S subunit of the bacterial ribosome.

2. Ribosomes and protein synthesis:
- Ribosomes are cellular structures responsible for protein synthesis in all living organisms.
- In bacteria, ribosomes are composed of two subunits: the small 30S subunit and the large 50S subunit. Together, they form the 70S ribosome.
- Ribosomes play a crucial role in the translation of genetic information from mRNA into proteins.

3. Mode of action of streptomycin:
- Streptomycin binds to the 30S subunit of the ribosome, specifically to a region known as the 16S rRNA.
- This binding interferes with the normal assembly of the ribosome and prevents the formation of functional 70S ribosomes.
- As a result, protein synthesis is inhibited, leading to the disruption of bacterial growth and viability.
- Streptomycin's binding to the ribosome also causes misreading of the genetic code, leading to the production of defective proteins.

4. Selective toxicity:
- Streptomycin exhibits selective toxicity towards bacteria due to structural differences in their ribosomes compared to eukaryotic ribosomes.
- Eukaryotic ribosomes are larger (80S) and have structural differences that make them less susceptible to the binding of streptomycin.
- This selective targeting of bacterial ribosomes allows streptomycin to specifically inhibit bacterial protein synthesis without affecting human cells.

In conclusion, streptomycin exerts its antibacterial activity by preventing the formation of 70S ribosomes in bacteria. This inhibition of ribosome assembly disrupts protein synthesis and leads to the impairment of bacterial growth and viability.