Question

'Abirin' and 'ricin' are toxic plant proteins which inhibit the protein synthesis in eukaryotic ribosomes by inactivating the

• A. 40S subunit
• B. 60S subunit
• C. 60S and 40S
• D. Genetic code

Answer 1

The correct option is B 60S subunit

Abirin and ricin are extremely toxic proteins, present in castor bean. These toxins inhibit the protein synthesis by inactivating 60S subunit of eukaryotic ribosomes by depurinating a specific adenosine in 23S rRNA. As binding of 60S ribosomal subunit to a complex of mRNA, 40S subunit and initiation factors marks the formation of initiation complex which in turn signal the beginning of translation. The pairing of anticodon of tRNA with the mRNAs initiation codon induces binding of 50S ribosomal subunit. These proteins do not bind to 40S subunit of ribosome or to genetic code. Correct answer is B.