9 public questions tagged with this topic.
The poly-A tail protects eukaryotic mRNA from degradation and aids in translation efficiency.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
The poly-A tail protects eukaryotic mRNA from degradation and aids in translation.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance DNA Replication - Semiconservative and Machinery
The **poly-A tail stabilizes mRNA and prevents degradation**, aiding in efficient translation.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance DNA Replication - Semiconservative and Machinery
Mature mammalian messenger RNAs carry polyadenine tail of approximately eighty to two hundred nucleotides on average, longer two hundred to two hundred fifty in newly synthesized nuclear RNAs shortened in cytoplasm, while yeast tails average seventy to eighty residues. Initial addition of ten to twelve adenines is slow distributive phase, then nuclear polyadenine binding protein PABPN1 stimulates processive synthesis to full length. Tail length influences binding of one PABPC per twenty-seven adenines, forming compact ribonucleoprotein particle. Progressive deadenylation by CCR4-NOT complex in cytoplasm regulates translation and decay. Oocyte cytoplasmic polyadenylation lengthens tails to activate translation.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6: Poly(A) tail length 80-200; Lodish 9th ed., Regulation of poly(A) length
Polyadenylation of eukaryotic messenger RNA occurs exclusively at three prime end, downstream of AAUAAA signal where nascent RNA is cleaved by endonuclease CPSF73. Polyadenylate polymerase PAP adds continuous stretch of adenine residues to new three hydroxyl group in template-independent manner using ATP. Location exclusively three prime is critical for defining messenger RNA orientation, promoting nuclear export, protecting against three prime to five prime exosome decay, and enhancing translation initiation via interaction between polyadenine binding protein PABPC and eIF4G that circularizes mRNA. Replication-dependent histone mRNAs are exception lacking polyadenylation.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: Polyadenylation at 3' end; Alberts 7th ed., Poly(A) tail addition site
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
Linkage between seven methylguanosine cap and first transcribed nucleotide involves unusual five prime to five prime triphosphate bridge, chemically distinct from standard three prime to five prime phosphodiester backbone connecting nucleotides within chain. Reaction catalyzed by guanylyltransferase creates G-five prime ppp five prime-N arrangement where three phosphate groups link inverted guanosine to RNA, blocking free five prime phosphate. Such inverted connectivity makes RNA resistant to five prime to three prime exonucleases Xrn1 and Xrn2 because exonucleases require free monophosphate entry site, thus protecting messenger RNA stability in both nucleus and cytoplasm.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: 5'-5' triphosphate bond of cap; Alberts et al., Mechanism of capping
PABP accurately identifies the binding site, binding partner, or molecular interaction described in this question. In Acid, Base, pH, molecular recognition and binding specificity are governed by complementary shape, charge, and hydrophobic interactions between molecules. PABP binds at the specified location due to its structural complementarity and specific non-covalent or covalent interactions. The other options (RNA pol II, ribosome directly, and tRNA) describe binding to different sites, involve different types of molecular interactions, or represent incorrect binding partners.
Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 2
recruiting ribosome is the scientifically accurate answer to this question. Within the study of Acid, Base, pH, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of recruiting ribosome directly address what is being asked. Among the other options, preventing degradation, splicing mRNA, and terminating translation do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.
Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 2
