Question

Describe three ways RNA is altered after it is transcribed.

Short answer

The three ways RNA is altered after it is transcribed are through capping at the 5' end, splicing to remove introns and join exons, and polyadenylation at the 3' end.

Step-by-step solution

Description of Capping

The first modification that happens to RNA is capping. This occurs at the 5' end of the pre-mRNA molecule. During capping, 7-methylguanosine is added to the pre-mRNA transcript, forming a 5'-5' triphosphate bridge. This cap is important for the stability of the mRNA and plays a crucial role in the translation process later on by helping the ribosome identify the start of the mRNA.

Description of Splicing

The second modification is splicing. During splicing, the introns (regions of the RNA sequence that do not code for proteins) are removed and the exons (regions that do code for proteins) are joined together. This is done by a protein-RNA complex called spliceosome. This process ensures that only protein-coding sequences are included in the final, mature mRNA transcript.

Description of Polyadenylation

The final modification is called polyadenylation which happens at the 3' end of the mRNA molecule. Here, a poly-A tail consisting of approximately 200 adenine bases is added to the mRNA transcript. The poly-A tail protects the mRNA from degradation and assists in the export of the mature mRNA from the nucleus to the cytoplasm.