A pre-mRNA must be processed to produce the final mRNA product of a gene-which of the following is NOT a normal processing step?

Question

A pre-mRNA must be processed to produce the final mRNA product of a gene-which of the following is NOT a normal processing step?

Group of answer choices

Addition of a 5' cap

Splicing out of any introns

Addition of a ribosome binding site

Addition of a 3' poly(A) tail

Answer 1

Hi,

The addition of the RBS is not part of the premRNA processing. In eukaryotes the RBS is referred to as the "Kozak" sequence. The Kozak sequence is located in the 5' untranslated region, meaning that the ribosome binds to this region and will start scanning the mRNA transcript until it hits the start codon. Once it hits the start codon translation will begin.

Answer 2

Addition of a ribosome binding site (RBS) is not a part of the pre-mRNA processing sequence. The RBS is a portion of the start codon of an already mature mRNA strand.

1. The 5' cap serves as a protection to reduce degradation of the mRNA sequence
2. The 3' Poly-A tail also provides protection from degradation, it serves as an exit 'pass' from the nucleus into the cytoplasm, and it contains proteins that are required to begin translation to become a polypeptide once in the cytoplasm
3. Intron splicing is the final step of pre-mRNA processing as it removes the non-coding sequences of RNA that have no purpose (as far as we know). Once the introns are spliced out, you are left with a mature mRNA strand of exons