Texas A&M University (TAMU) BIOL111 Introductory Biology I Exam 3 Practice Exam

The primary function of the cap added to mRNA in eukaryotes is to aid in ribosome attachment. The 5' cap is a modified guanine nucleotide that is added to the beginning of the mRNA transcript during processing. This cap structure is critical for several reasons.

First, it serves as a recognition signal for the ribosome, facilitating the binding of the ribosome to the mRNA, which is essential for the initiation of translation. Without this cap, the ribosome would have difficulty identifying the mRNA, leading to inefficient protein synthesis.

Additionally, the cap protects the mRNA from degradation by nucleases in the cytoplasm, thereby increasing the stability of the mRNA molecule. This stability is important for ensuring that there is sufficient mRNA available for translation into protein.

Furthermore, while the cap contributes to the overall process of gene expression and is essential for proper mRNA processing and nuclear export, its most immediate and direct role is to enable efficient ribosome attachment, which is crucial for translation.