pre mRNA to mRNA Steps

Transcription

Process in the nucleus where RNA polymerase II synthesizes a complementary RNA strand from the DNA template, forming pre-mRNA.

5’ Capping

A 7-methylguanosine cap is added to the 5′ end of the pre-mRNA to protect it from degradation, assist ribosome binding, and aid in nuclear export.

Splicing

The spliceosome removes introns (non-coding regions) and joins exons (coding regions) together to form a continuous coding sequence. Alternative splicing can produce different mRNAs from the same gene.

3′ Polyadenylation (Poly-A Tail Addition)

A chain of about 100-250 adenine nucleotides is added to the 3′ end by poly-A polymerase to increase stability, help with nuclear export, and assist translation initiation.

Export from the Nucleus

The mature mRNA, now capped, spliced, and polyadenylated, exits the nucleus through nuclear pores to enter the cytoplasm for translation.

Purpose of RNA Processing

Converts unstable pre-mRNA into mature mRNA that can be translated efficiently and accurately into protein.

Location of Each Step

All processing (capping, splicing, polyadenylation) occurs in the nucleus before the mature mRNA is exported to the cytoplasm.

Enzyme for Transcription

RNA Polymerase II.

Complex Responsible for Splicing

The spliceosome, which is made of snRNPs (small nuclear ribonucleoproteins).

Function of Poly-A Tail

Increases mRNA stability, helps export it from the nucleus, and aids in translation.