Question

Streptomycin binds the small subunit of prokaryotic ribosomes and A. causes premature release of the incomplete peptide. B. prevents binding of the \(40 S\) and 605 subunits. C. interferes with initiation of protein synthesis. D. inhibits peptidyl transferase activity. E. acts as an N-glycosidase.

Short answer

Answer: Streptomycin interferes with the initiation of protein synthesis by binding to the small (30S) subunit of the prokaryotic ribosome and causing mistranslation of the genetic code, which results in a non-functional, incorrect protein being synthesized.

Step-by-step solution

Understand Streptomycin and its mode of action

Streptomycin is an aminoglycoside antibiotic drug that targets prokaryotic cells, such as bacteria. It specifically binds to the small subunit of prokaryotic ribosomes, which plays an essential role in protein synthesis. Before proceeding through the given options, it is crucial to have a basic understanding of ribosomes and protein synthesis in prokaryotes.

Analyze the given options

For each option, we will now evaluate whether they correctly describe how Streptomycin binds the small subunit and interferes with protein synthesis. A. Causes premature release of the incomplete peptide - This option suggests that Streptomycin causes the ribosome to release the peptide before it is fully synthesized. Let's examine other options before choosing. B. Prevents binding of the \(40S\) and \(605\) subunits - This option refers to eukaryotic ribosome subunits, not prokaryotic ribosomes. Prokaryotic ribosomes are composed of the \(30S\) and \(50S\) subunits, so this option is incorrect. C. Interferes with initiation of protein synthesis - This option indicates that Streptomycin may affect the start of protein synthesis. We'll keep this in mind and analyze the other options. D. Inhibits peptidyl transferase activity - Peptidyl transferase is an enzymatic activity of ribosomes that catalyzes peptide bond formation during protein synthesis. If Streptomycin blocks this enzyme, it would disrupt protein synthesis by not allowing the chain to grow. This is another potential mechanism of action. E. Acts as an N-glycosidase - N-glycosidases are enzymes that cleave glycosidic bonds between saccharide or sugar molecules. This option suggests that Streptomycin acts like an N-glycosidase, which is unrelated to the ribosome-binding mechanism.

Select the correct choice for Streptomycin's mode of action

Having analyzed each option, we can rule out options B and E. Now, it is time to choose between options A, C, and D. The correct choice is C. Streptomycin interferes with the initiation of protein synthesis. It does this by binding to the small (30S) subunit of the prokaryotic ribosome and causes the mistranslation of the genetic code, which results in a non-functional, incorrect protein being synthesized. In conclusion, Streptomycin binds the small subunit of prokaryotic ribosomes and: C. Interferes with the initiation of protein synthesis.

Key concepts

Prokaryotic Ribosomes

Prokaryotic organisms, such as bacteria, are simpler life forms without a true nucleus. To make the proteins they need for survival, they rely on tiny cellular machines called ribosomes. These ribosomes are different from those found in eukaryotic cells (such as human cells) and consist of two subunits designated as the 30S (small subunit) and the 50S (large subunit). Together, these subunits work meticulously to translate the genetic code into functional proteins.

During protein synthesis, the 30S subunit is responsible for decoding the messenger RNA (mRNA), while the 50S subunit joins amino acids to form a polypeptide chain. Disruption at any stage of this process can halt protein synthesis, which often results in bacterial growth inhibition or cell death. This makes prokaryotic ribosomes a prime target for antibiotic drugs, like Streptomycin, that aim to control bacterial infections.

Protein Synthesis in Prokaryotes

The process of making proteins in prokaryotes is fundamental to their growth and reproduction and is known as protein synthesis or translation. It is a complex yet beautifully coordinated process that occurs within the ribosome and involves several key steps: initiation, elongation, and termination.

During Initiation, ribosomal subunits assemble around a starting point on the mRNA template. The Elongation phase is then marked by the addition of amino acids to the growing polypeptide chain through a series of enzymatic reactions. Termination occurs when the ribosome reaches a stop codon on the mRNA, signaling the end of the protein synthesis. Disruption of any of these steps can be lethal to bacteria as it stops the production of essential proteins, highlighting the importance of antibiotics that interfere with protein synthesis.

Antibiotics and Bacterial Inhibition

Antibiotics are powerful medicines used to fight bacterial infections. They function by targeting various bacterial structures and processes, one of which is the ribosome. Specifically, antibiotics like Streptomycin are designed to inhibit protein synthesis in prokaryotes, which is vital to bacterial survival.

Streptomycin mode of action is particularly clever: it binds to the 30S subunit of the prokaryotic ribosome and interferes with the initiation phase of protein synthesis. By doing so, it introduces errors into the genetic code translation or even prevents the proper assembly of the ribosome subunits. This mistake leads to malfunctioning proteins that cannot sustain bacterial life, effectively inhibiting bacterial growth. Understanding how this antibiotic works helps researchers develop better treatments and manage antibiotic resistance, ensuring that we stay one step ahead in the battle against bacterial infections.