9 public questions tagged with this topic.
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
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
Five prime cap of eukaryotic messenger RNA contains modified nucleotide seven methylguanosine, formed after addition of guanosine not encoded by DNA. Guanine base is methylated at N7 position by cap methyltransferase RNMT using S-adenosylmethionine SAM as methyl donor, creating positively charged quaternary ammonium essential for specific recognition by eukaryotic initiation factor eIF4E during translation. Additional 2'-O methylations of first nucleotide creating cap one and second nucleotide creating cap two occur via CMTR1 and CMTR2 methyltransferases in higher eukaryotes enhancing innate immune evasion and translation efficiency.
Ref: Berg et al., Biochemistry, 9th ed., Chapter 28: 5' cap contains 7-methylguanosine; Alberts 7th ed., Cap methyltransferase mechanism
Five prime capping of messenger RNA occurs predominantly in nucleus, co-transcriptionally while polymerase II remains bound to DNA template. Capping enzymes RNA triphosphatase, guanylyltransferase, and methyltransferase are recruited to promoter-proximal polymerase via binding to Serine five phosphorylated C-terminal domain. Enzymatic addition of 7-methylguanosine via five prime to five prime triphosphate linkage happens within first minutes of transcription when nascent RNA emerges. Resulting cap binding complex CBP20 and CBP80 protects transcript from nuclear exonucleases, facilitates splicing of first intron, and directs export through nuclear pore mediated by NXF1 pathway.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: 5' capping occurs in nucleus cotranscriptionally; Alberts et al., Nuclear processing compartments
Eukaryotic five prime cap harbors highly unusual five prime to five prime linkage instead of canonical three prime to five prime phosphodiester found in RNA backbone. After RNA triphosphatase generates diphosphate RNA, guanylyltransferase hydrolyzes GTP to GMP and catalyzes attack of diphosphate RNA on alpha phosphate forming Gp pppN triphosphate bridge linking guanine five prime to first nucleotide five prime. Three phosphate groups create 5'-5' connection. Subsequent methylation at N7 of guanine and ribose 2' O positions generate cap zero, cap one, cap two structures resistant to decapping and exonuclease attack.
Ref: Berg et al., Biochemistry, 9th ed., Chapter 28: 5'-5' triphosphate cap linkage; Lodish 9th ed., Mechanism of guanylyltransferase forms unusual linkage
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
monocistronic 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 monocistronic directly address what is being asked. Among the other options, polycistronic, overlapping, and non-coding 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
