Question

Which of the following is TRUE?

I. Nucleolus is also the site where other RNA-protein complexes, including telomerase and signal recognition particle, are processed,
II. 5S rRNA is located within the nucleolus,
III. The genes for 5.8S, 18S, 28S, FRNAS are clustered in tandem arrays on 5 different human chromosomes,
IV. 45S FRNA splits to form the 18S, 5.8S, and 28S rRNAs?
A) I and II
B) II and III
C) III and IV
D) I and IV

Answer 1

Statements I and IV regarding nucleolus functions and rRNA processing are TRUE, making the correct answer D) I and IV. The nucleolus is involved in rRNA transcription and processing of RNA-protein complexes, and the 45S pre-rRNA is processed to form the 18S, 5.8S, and 28S rRNAs. Option D is correct.

Step-by-step explanation:

The question involves understanding the structure and functions of the nucleolus, the types of ribosomal RNA (rRNA), and how they are processed in eukaryotic cells. Statement I is TRUE as the nucleolus is the site where rRNA is transcribed and where other RNA-protein complexes are processed.

However, Statement II is FALSE, as 5S rRNA is a product of RNA polymerase III activity and is not located within the nucleolus, but rather in the nucleus outside of the nucleolus. Statement III is FALSE because the genes for 5.8S, 18S, and 28S rRNA are indeed clustered in tandem arrays but are found on a few human chromosomes, not five.

Lastly, Statement IV is TRUE as the 45S pre-rRNA is transcribed as a precursor that is subsequently processed (split) to form the 18S, 5.8S, and 28S rRNAs. This occurs in the nucleolus, and then the mature rRNAs are assembled into ribosomal subunits. Therefore, the correct answer is D) I and IV.