Eukaryotic mRNA attaches to ribosome during translation due to:
**Core Concept**
Eukaryotic mRNA attaches to ribosomes during translation due to a complex process involving specific sequences and proteins that facilitate the initiation of protein synthesis. This process is crucial for ensuring accurate and efficient translation of the genetic code into a polypeptide chain. The key players involved in this process include the small subunit of the ribosome, initiation factors, and the mRNA itself.
**Why the Correct Answer is Right**
The correct answer is **A. 5' cap recognition by eIF4E**. During translation initiation, the eukaryotic mRNA is recognized by the small subunit of the ribosome through a process mediated by the 5' cap recognition by eIF4E. The 5' cap, also known as the m7G cap, is a modified guanine nucleotide that is added to the 5' end of the mRNA during transcription. eIF4E, a protein that binds to the 5' cap, plays a critical role in recruiting the mRNA to the ribosome and facilitating the initiation of translation. This process is essential for ensuring the accurate and efficient translation of the genetic code into a polypeptide chain.
**Why Each Wrong Option is Incorrect**
* **Option B:** **Recognition of poly-A tail by PABP** - While the poly-A tail is indeed a crucial element of the mRNA, its recognition by PABP (Poly-A Binding Protein) is not directly involved in the attachment of the mRNA to the ribosome during translation initiation.
* **Option C:** **Recognition of start codon by initiation factors** - While the start codon (AUG) is essential for translation initiation, its recognition by initiation factors is not the primary mechanism by which the mRNA attaches to the ribosome.
* **Option D:** **Recognition of stop codon by release factors** - The stop codon (UAA, UAG, or UGA) is recognized by release factors during translation termination, not during translation initiation, and is not directly involved in the attachment of the mRNA to the ribosome.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the 5' cap recognition by eIF4E is a critical step in translation initiation, and mutations or alterations in this process can lead to various diseases, including certain types of cancer and neurodegenerative disorders.
**Correct Answer:** A. 5' cap recognition by eIF4E