9 public questions tagged with this topic.
mRNA is not translated in the nucleus; it must first be processed and transported to the cytoplasm.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
In eukaryotes, a 5' cap (methyl guanosine triphosphate) is added to mRNA to enhance stability and translation efficiency.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
The poly-A tail is added to the 3' end of mRNA, not the 5' end.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
The spliceosome removes introns from pre-mRNA and joins the exons together to form mature mRNA.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
Transcription is the first step in gene expression, producing pre-mRNA, which undergoes processing before translation.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
Post-transcriptional modifications occur in the nucleus, not in the cytoplasm.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
Poly-A polymerase adds a poly-A tail to mRNA to enhance its stability and regulate translation.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance DNA Replication - Semiconservative and Machinery
Polyadenylation signal in nascent messenger RNA consists of highly conserved hexamer AAUAAA located ten to thirty nucleotides upstream of CA dinucleotide cleavage site. Recognized by WDR33 and CPSF30 subunits of cleavage and polyadenylation specificity factor CPSF through base stacking in zinc finger pockets. Mutation of AAUAAA to AAGAAA drastically reduces cleavage efficiency and causes read-through transcription. Auxiliary upstream sequence elements USE enriched in uridine and downstream GU-rich downstream sequence element DSE bound by CstF enhance recognition. Identical DNA motif is AATAAA.
Ref: Berg et al., Biochemistry, 9th ed., Chapter 28: Poly(A) signal AAUAAA; Lodish 9th ed., CPSF recognition of AAUAAA hexamer
Five prime cap shields messenger RNA from rapid degradation mediated by highly processive five prime to three prime exonucleases. Without cap, uncapped pre-mRNAs bearing five prime monophosphate are substrates for nuclear Xrn2 Rat1 and cytoplasmic Xrn1 surveillance pathways that degrade aberrant or decapped transcripts as part of quality control. Cap physically blocks entry into exonuclease active site channel and recruits cap binding complex CBP20-CBP80 that sterically occludes end. It also masks RNA from innate immune sensors RIG-I and IFIT that detect exposed five prime triphosphates of viral RNAs.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6: 5' cap protects from 5'-3' exonucleases; Lodish 9th ed., Mechanism of mRNA stability
