Why?

Eukaryotic mRNA undergoes extensive processing before it can be translated into protein. This processing is essential for several reasons:

1. Protection from Degradation:

* 5' Cap: A 7-methylguanosine cap is added to the 5' end of the mRNA molecule. This cap protects the mRNA from degradation by exonucleases, enzymes that break down nucleic acids from the ends.

* Poly(A) Tail: A long chain of adenine nucleotides (poly(A) tail) is added to the 3' end of the mRNA. This tail also protects the mRNA from degradation and helps in its transport out of the nucleus.

2. Efficient Translation:

* 5' Cap: The 5' cap is recognized by the small ribosomal subunit, facilitating the initiation of translation.

* Poly(A) Tail: The poly(A) tail is recognized by proteins involved in translation initiation and termination.

3. Nuclear Export:

* The processed mRNA is recognized by nuclear export proteins, allowing it to be transported out of the nucleus and into the cytoplasm, where translation occurs.

4. Splicing:

* Eukaryotic genes contain non-coding regions called introns. These introns must be removed from the pre-mRNA transcript before it can be translated. This process is called splicing, and it ensures that only the coding sequences (exons) are translated into protein.

5. Alternative Splicing:

* Splicing can occur in different ways, leading to the production of multiple protein isoforms from a single gene. This allows for greater protein diversity and complexity.

In contrast, prokaryotic mRNA does not require extensive processing. Prokaryotic genes are typically organized in operons, where multiple genes are transcribed as a single mRNA molecule. Prokaryotic mRNA does not have a 5' cap, a poly(A) tail, or introns. Therefore, it can be translated directly after transcription.