Q. What is the importance of capping in translation?
Capping protects mRNAs at their termini against attack by phosphatases and other nucleases and promotes mRNA function at the level of initiation of translation.
Q. What does the guanine cap do?
The 5′ cap has four main functions: Regulation of nuclear export; Prevention of degradation by exonucleases; Promotion of translation (see ribosome and translation);
Q. Why is it necessary for capping to occur before the mRNA has been completely synthesized?
In the capping step of mRNA processing, a 7-methyl guanosine (shown at left) is added at the 5′ end of the mRNA. The cap protects the 5′ end of the mRNA from degradation by nucleases and also helps to position the mRNA correctly on the ribosomes during protein synthesis.
Q. What is the purpose of the poly-A tail and the GTP cap?
5′ cap and poly-A tail Both the cap and the tail protect the transcript and help it get exported from the nucleus and translated on the ribosomes (protein-making “machines”) found in the cytosol 1start superscript, 1, end superscript. The 5′ cap is added to the first nucleotide in the transcript during transcription.
Q. What is the function of 5 caps and 3 poly-A tails?
The 5′ cap protects the nascent mRNA from degradation and assists in ribosome binding during translation. A poly (A) tail is added to the 3′ end of the pre-mRNA once elongation is complete.
Q. Are poly-A tails encoded DNA?
The poly(A) tail confers stability to the mRNA and enhances translation efciency. The poly(A) tail can be encoded in the DNA template by using an appropriately tailed PCR primer, or it can be added to the RNA by enzymatic treatment with E.
Q. Why are some poly-A tails longer?
18. Different mRNA molecules can have poly-A tails of different lengths. Considering the purpose of adding the poly-A tail (from the previous question), why are some tails longer than others? It prevents the information-carrying part of the mRNA from being destroyed by the exonucleus before a polypeptide can be formed.
Q. What happens if a poly A tail is not added?
The rate of deadenylation may also be regulated by RNA-binding proteins. Once the poly(A) tail is removed, the decapping complex removes the 5′ cap, leading to a degradation of the RNA. Several other proteins are involved in deadenylation in budding yeast and human cells, most notably the CCR4-Not complex.
Q. How does the poly-A tail affect mRNA stability?
the poly-A tail is shortened (presumably during translation) by the CCR4-NOT and PARN complexes. as the poly-A shortens, there are less PABP that can associate with the eIF4F. Once the poly-A is short enough, the eIF4F-cap complex is less stable, leading to successful recruitment of the decapping complex to the cap.
Q. Why is RNA capped?
The m7G cap, also known as cap 0 structure, is essential for the majority of protein translation in vivo. The m7G cap also protects the mature mRNA from degradation, allows for a regulated degradation mechanism, enhances pre-RNA splicing and directs nuclear export.
