Which of the following is true about capping of RNA following its synthesis
**Core Concept**
RNA capping is a post-transcriptional modification that protects the 5' end of RNA molecules from degradation and enhances their stability. This process involves the addition of a methylated guanine nucleotide to the 5' end of the RNA transcript.
**Why the Correct Answer is Right**
The capping of RNA is mediated by the enzyme RNA guanylyltransferase, which catalyzes the transfer of a GTP molecule to the 5' end of the RNA transcript. This reaction is followed by the subsequent methylation of the 5' cap by a methyltransferase enzyme. The 5' cap plays a crucial role in the nuclear export of RNA, translation initiation, and the prevention of RNA degradation. The capping of RNA also helps to recruit the nuclear RNA export machinery, including the exportin 1 protein, to facilitate the export of RNA from the nucleus to the cytoplasm.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the molecular mechanism of RNA capping or the enzymes involved in this process.
**Option B:** This option is incorrect because it does not accurately describe the role of the 5' cap in RNA stability and translation initiation.
**Option C:** This option is incorrect because it does not mention the involvement of methyltransferase enzymes in the methylation of the 5' cap.
**Clinical Pearl / High-Yield Fact**
The 5' cap is essential for the nuclear export of RNA, and mutations in the genes encoding the capping enzymes can lead to defects in RNA export and stability, resulting in various human diseases, including some forms of cancer and neurological disorders.
**Correct Answer: C. The 5' cap is protected from degradation by methyl groups, which enhances RNA stability.**