Which statement best describes the 5' cap and 3' poly(A) tail on mRNA?

Which statement best describes the 5' cap and 3' poly(A) tail on mRNA?

• A. 5' cap only
• B. 3' poly(A) tail only
• C. Both 5' cap and 3' poly(A) tail
• D. Neither cap nor tail

Answer: (C)

In mature eukaryotic mRNA, there is both a 5' cap and a 3' poly(A) tail. The 5' cap is a modified guanine nucleotide added very early in transcription; it helps recruit the ribosome to start translation and protects the 5' end from degradation, while also facilitating export from the nucleus. The 3' poly(A) tail is added after transcription and consists of a long stretch of adenines; it protects the mRNA from exonucleases, enhances stability, and, with poly(A)-binding proteins, boosts translation efficiency by helping ribosomes recycle. Because both features contribute to stability and efficient translation, the statement that mRNA has both is the best description. Note that some exceptions exist (like certain histone mRNAs that lack a poly(A) tail), but the common case for most eukaryotic mRNA includes both.

In mature eukaryotic mRNA, there is both a 5' cap and a 3' poly(A) tail. The 5' cap is a modified guanine nucleotide added very early in transcription; it helps recruit the ribosome to start translation and protects the 5' end from degradation, while also facilitating export from the nucleus. The 3' poly(A) tail is added after transcription and consists of a long stretch of adenines; it protects the mRNA from exonucleases, enhances stability, and, with poly(A)-binding proteins, boosts translation efficiency by helping ribosomes recycle. Because both features contribute to stability and efficient translation, the statement that mRNA has both is the best description. Note that some exceptions exist (like certain histone mRNAs that lack a poly(A) tail), but the common case for most eukaryotic mRNA includes both.