Prokaryotic mRNA and tRNA 5' Ends Explained
The structure of the 5' end of mature prokaryotic messenger RNA (mRNA) and transfer RNA (tRNA) molecules differs significantly due to their distinct synthesis and processing pathways.
mRNA 5' End Structure
- Prokaryotic mRNA synthesis begins with RNA polymerase initiating transcription.
- The very first nucleotide added during transcription contains its inherent triphosphate group ($\text{pppN-}$).
- This initial triphosphate group is typically not removed during the processing of mature prokaryotic mRNA.
- Therefore, the 5' end of most mature prokaryotic mRNAs carries a triphosphate group.
tRNA 5' End Structure
- Prokaryotic tRNAs are transcribed as larger precursor molecules.
- These precursors undergo significant processing, including cleavage by specific enzymes (RNases).
- Enzymatic cleavage during maturation typically removes nucleotides from the 5' end of the precursor transcript.
- This processing action results in the 5' end of the mature tRNA having a monophosphate group ($\text{p}`).
Conclusion
Based on these processing differences, the 5' end of mature prokaryotic mRNAs has a triphosphate group, while the 5' end of mature prokaryotic tRNAs has a monophosphate group.
Important Questions from Replication Transcription Splicing and Translation
Messenger RNAs (mRNAs) translate to generate polypeptides and the translation terminates at the UGA, UAG or UAA stop codons. The AGA codon acts as additional stop codon in the mitochondria. The longest possible polypeptide(s) that can be hypothetically translated in the cytosol and/or mitochondria, from the given full length mRNA sequence (36 nucleotides) is/are
5'-AACACCAUGACCCAUGUGGCGAGACGGUAGUUAAAA- 3'
- Which of the following statements about initiation of DNA replication in eukaryotes is/are true?
Match the drugs in Group I with their mechanism of action in Group II.
Group I Group II P) Paclitaxel 1) Inhibits protein translation Q) Colchicine 2) Inhibits microtubule depolymerization R) Etoposide 3) Inhibits DNA replication S) Methotrexate 4) Alkylates DNA 5) Inhibits dihydrofolate reductase 6) Inhibits microtubule polymerization Match the enzyme (Column I) with its corresponding function (Column II).
Column I Column II P. Primase 1. RNA dependent RNA synthesis Q. Reverse transcriptase 2. DNA dependent DNA synthesis R. RNA Replicase 3. RNA dependent DNA synthesis S. DNA Polymerase III 4. DNA dependent RNA synthesis Which of the following statements regarding the below mentioned mRNA sequence is/are TRUE?
5`-UGAUGAGCCUUAACCGGGAACGAAUUUAAG-3`
