Ricin is among the most toxic natural products known because. a single molecule

Question

Ricin is among the most toxic natural products known because. a single molecule of the RTB fragment of ricin penetrates mammalian cells forming a non-specific ion channel in the plasma membrane. the RTA fragment of ricin is an enzyme capable of inactivating a very large number of mammalian ribosomes, the RTB fragment of ricin binds to the carboxyl terminus of nascent polypeptides hatting translation. the RTA fragment of ricin is a ubiquitin ligase that targets the 28S rRNA for degradation. the Transportation Security Agency (TSA) is incapable of distinguishing ricin from baking powder. RNA polymerase II transcription produces a primary transcript that includes a continuous open reading frame. both exon and intron sequences. only exon sequences. only intron sequences. None of the above

Explanation / Answer

(24) Ricin produced as proteinaceous by-product produced during castor oil from castor beans (ricinus community seeds) in large quantity. Its high toxicity is due to grater absorption in GI tract by endocytosis and cause mucosal injuries. On molecular basis, its peptides act as N-glycosidase it removes glycosidic bond and left apurinated Adanine residue situated at 4324 position (after G-4323) in 28SrRNA. Its specialized bipartite structure allow it to bind irreversibally and stop protein synthesis which results in to cell death.

For given question above (que.-24) appropriate answer would be second i.e. RTA fragment of ricin protein is an enzyme capable of inactivating ribosomes.

It do not excert its effect through ion channe or through C- terminal halting translation or ubiquitinisation or TSA.

Ans 25:

In eucaryotic system RNA POL-II is the only enzyme that transcribe mRNA transcript. Other RAN POL like RNA POL-I and RNA POL-III transcribes rRNA and tRNA transcript.

mRNA transcript is nacent RNA and it contain both intron and exon.

Introns are the sequences that are seperated by exones. Exones are important as they are the sequences that produces functional protein. In eucaryotic genom both are scattered through out the sequence of DNA. RNA POL do not differentiate between intron and exon. After the cytoplasmic transport from nucleus to cytoplasm introns are removed by process name as splicing. To make continus open reading fram which contain only exon as processed product of primary transcript.

So for above question(question 25) appropriate answer would be second i.e. PRIMARY TRANSCRIPT contain BOTH INTRON AND EXON.

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