MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A genetics researcher is studying a novel eukaryotic gene that produces a protein with a molecular weight of 50 kDa. They discover that the initial RNA transcript is significantly longer than the mature mRNA found in the cytoplasm. This difference in length is primarily due to the removal of specific non-coding sequences. What is the name of this crucial processing step?
- APolyadenylation
- BSplicing
- CTranscription
- D5' capping
Show answer & explanationAnswer & explanation
Correct answer: B. Splicing
In eukaryotic mRNA processing, splicing is the removal of non-coding introns from the pre-mRNA transcript, leaving behind the coding exons which are then ligated together to form the mature mRNA. This process accounts for the observed difference in length.
Why the other options are wrong
- A. Polyadenylation is the addition of a poly-A tail to the 3' end, which doesn't explain the removal of internal sequences.
- C. Transcription is the synthesis of RNA from a DNA template, which produces the initial, longer transcript.
- D. 5' capping is the addition of a modified guanine nucleotide to the 5' end, which also doesn't explain internal sequence removal.
Eukaryotic mRNA Processing
A series of modifications that a pre-mRNA molecule undergoes in eukaryotes before it can be translated into a protein. These steps include 5' capping, splicing, and polyadenylation.
- Occurs in the nucleus.
- Converts pre-mRNA (primary transcript) to mature mRNA.
- Includes 5' capping, splicing (intron removal), and 3' polyadenylation.
- Ensures mRNA stability, transport, and efficient translation.
Memory trick: MRNA's a CAPtain, then SPLICE, then a POLY tail.