What is the function of the 5' cap and 3' poly-A tail in mRNA processing?

What is the function of the 5' cap and 3' poly-A tail in mRNA processing?

• A. The 5' cap protects the 5' end and helps ribosome binding; the 3' poly-A tail enhances stability and export.
• B. The 5' cap signals termination; the poly-A tail starts translation.
• C. The 5' cap and poly-A tail have no known function.
• D. The 5' cap destabilizes mRNA; the poly-A tail inhibits export from the nucleus.

Answer: (A)

The main idea this question tests is how the 5' cap and the 3' poly-A tail make an mRNA molecule stable, export-ready, and efficient for translation. The 5' cap is a modified guanine added to the front end of the transcript early in processing. It protects the 5' end from being chewed up by exonucleases and is recognized by cap-binding proteins that recruit the ribosome to start translation. The cap also supports proper RNA processing and helps with export from the nucleus. The 3' poly-A tail is a string of adenine residues added to the back end. It safeguards the mRNA from 3' exonucleases, increases overall mRNA stability, and, through binding proteins, aids in exporting the mRNA to the cytoplasm. It also helps translation efficiency by promoting a circular mRNA form where the poly-A binding proteins interact with the translation machinery to enhance ribosome recycling. So, these features don’t signal termination or start translation on their own, and they certainly don’t have no function or destabilize the mRNA. Their roles are to protect the message, enable export, and boost translation efficiency.

The main idea this question tests is how the 5' cap and the 3' poly-A tail make an mRNA molecule stable, export-ready, and efficient for translation. The 5' cap is a modified guanine added to the front end of the transcript early in processing. It protects the 5' end from being chewed up by exonucleases and is recognized by cap-binding proteins that recruit the ribosome to start translation. The cap also supports proper RNA processing and helps with export from the nucleus.

The 3' poly-A tail is a string of adenine residues added to the back end. It safeguards the mRNA from 3' exonucleases, increases overall mRNA stability, and, through binding proteins, aids in exporting the mRNA to the cytoplasm. It also helps translation efficiency by promoting a circular mRNA form where the poly-A binding proteins interact with the translation machinery to enhance ribosome recycling.

So, these features don’t signal termination or start translation on their own, and they certainly don’t have no function or destabilize the mRNA. Their roles are to protect the message, enable export, and boost translation efficiency.