15. Regarding gene expression of eukaryotes, which statement is correct?
(1) m-RNA and template DNA are has same sequence
(2) m-RNA and protein synthesis can occur simultaneously
(3) processing of hn-RNA yields m-RNA
(4) RNA polymerase can bind to promoters situated downstream of protein coding genes
(5) There is flexibility over only at last base of codon

Eukaryotic Gene Expression: Processing of hn-RNA Yields mRNA

Among the given options regarding eukaryotic gene expression, the correct statement is:

(3) Processing of hn-RNA yields m-RNA

Explanation of Each Option

1. m-RNA and template DNA have the same sequence

   • Incorrect. mRNA sequence is complementary to the DNA template strand but identical (except U replaces T) to the non-template (coding) strand. So, mRNA sequence matches the coding strand with uracil instead of thymine.

2. m-RNA and protein synthesis can occur simultaneously

   • Incorrect in eukaryotes. Transcription occurs in the nucleus, and translation occurs in the cytoplasm, so these processes are spatially and temporally separated. Simultaneous transcription and translation happen only in prokaryotes.

3. Processing of hn-RNA yields m-RNA

   • Correct. Heterogeneous nuclear RNA (hn-RNA), the initial transcript, undergoes processing steps such as 5′ capping, splicing to remove introns, and 3′ polyadenylation to become mature mRNA ready for export and translation.

4. RNA polymerase can bind to promoters situated downstream of protein coding genes

   • Incorrect. Promoters are generally located upstream (5′ direction) of genes to initiate transcription.

5. There is flexibility over only at last base of codon

   • Incorrect. The “wobble” position is the third base of the codon, not necessarily the last base in a general sense, and this flexibility allows some tRNAs to recognize multiple codons.

Additional Context

• hn-RNA Processing:
  In eukaryotes, the primary transcript (hn-RNA or pre-mRNA) contains both exons (coding sequences) and introns (non-coding sequences). Processing includes removal of introns by splicing, addition of a 5’ cap, and addition of a 3’ poly(A) tail, producing mature mRNA that can be translated into protein.

• Separation of Transcription and Translation:
  Unlike prokaryotes, eukaryotic cells compartmentalize transcription and translation, preventing their simultaneous occurrence35.

• Codon Wobble:
  The flexibility in base pairing occurs at the third nucleotide of the codon, allowing some tRNAs to pair with multiple codons that code for the same amino acid.

Summary

The correct understanding of eukaryotic gene expression is that processing of hn-RNA yields mature mRNA which is then transported out of the nucleus for translation. This makes option (3) the accurate statement.

Answer: (3) Processing of hn-RNA yields m-RNA