3) It is known that a certain gene of a eukaryotic cell contains 4 introns (two of 24 nucleotides and two of 36 nucleotides) and 3 exons (two of 120 nucleotides and one of 96 nucleotides). Determine: the number of nucleotides in the mRNA; number of codons in mRNA
In eucaryotic cells pre-mRNA contains both introns and exons, so the number of nucleotides is 456. But during splicing mRNA introns are removed and exons are ligated to each other. So except one modified G nucleotide (cap) on the 5`-end and poly-A tail on the 3`-end mRNA would consist of 3 exons (considering no alternative splicing) and therefore 336 nucleotides.
Codon consists of 3 nucleotides so to find the number of codons we should divide the number of nucleotides (336) by 3. The number of codons is 112.
The number of nucleotides in pre-mRNA (except cap and poly-A tail) is 456.
The number of nucleotides in mature mRNA (except cap and poly-A tail) is 336.
The number of codons in mRNA is 112.