Following intron splicing in the nucleus, a mature mRNA molecule consists of 500 nucleotides and is translated into a 110 amino acid protein. Given this, which of the following statements regarding this mRNA molecule would be true?

Question

Following intron splicing in the nucleus, a mature mRNA molecule consists of 500 nucleotides and is translated into a 110 amino acid protein.  Given this, which of the following statements regarding this mRNA molecule would be true?

Quizplus · Accepted Answer

11ecba2d_103c_b056_a3bf_a54e753a36a5_MD0008_00 In eukaryotic cells, nuclear genes are initially transcribed by RNA polymerase into pre-mRNA. Pre-mRNA is then converted into mature mRNA in a process that includes splicing to remove introns. Mature mRNA is then transported out of the nucleus into the cytoplasm, where it may be translated into protein by ribosomes. Each amino acid in a protein is encoded by a corresponding mRNA codon, a sequence of three consecutive nucleotides that binds the anticodon of a tRNA "charged" with a specific amino acid. Translation of mRNA (in the 5' to 3' direction) initiates at the start codon (AUG) and continues until a stop codon (UAA, UAG, or UGA) is reached. The stop codon does not code for an amino acid and instead binds a release factor that promotes dissociation of the translation complex. In addition, regions upstream of the start codon and downstream of the stop codon, referred to as untranslated regions (UTRs), do not code for amino acids. In this scenario, a mature mRNA molecule consisting of 500 nucleotides was translated into a 110 amino acid protein. Because each amino acid is encoded by a three-nucleotide codon, the number of nucleotides translated into this protein can be calculated as follows: 11ecba2d_103c_b057_a3bf_1b3b08f8aa1d_MD0008_00 110 AA x 3 nucleotides per codon=330 nucleotides Therefore, 330 nucleotides in this mRNA molecule code for amino acids (Choice A). The number of nucleotides that do not code for amino acids can then be calculated as follows: 11ecba2d_103c_d768_a3bf_333516ff1f00_MD0008_00 500 total nucleotides-330 coding nucleotides=170 noncoding nucleotides Therefore, 170 nucleotides in this mRNA molecule, including the stop codon and UTRs, do not code for amino acids. (Choice B) The question states that the mature mRNA molecule contained 500 nucleotides after intron splicing. Therefore, the original pre-mRNA molecule was most likely transcribed from a gene that contained more than 500 nucleotides. (Choice D) The average weight of an amino acid is 110 Da. Therefore, the approximate weight of a 110 amino acid protein is about 12,100 Da, or 12.1 kDa (1,000 Da = 1 kDa). Educational objective: Each amino acid in a protein is encoded by a corresponding three-nucleotide mRNA codon. However, mRNA molecules also include regions that are not translated into protein (ie, a stop codon and untranslated regions).

Following Intron Splicing in the Nucleus, a Mature MRNA Molecule