Question

A 3000 bp region of the human genome encodes two genes. One of the genes encodes a protein of 700 amino acids and the other gene encodes a protein of 310 amino acids. The mRNA sequences of the two genes do not contain any of the same nucleotide sequences. How is this possible?

That's all the information given. I think I'm supposed to mention terms like "reading frame" but this question doesn't make any sense

Answer 1

Yes mate, it is completely possible. A single genomic region can code for multiple mRNA sequences. It can happen due to variable mRNA editing, and reading frame is not entirely concerned with this question.

Due to a phenomena called alternate splicing/differential splicing , this situation is possible. Once mRNA is transcribed from DNA, then its editing takes place. Few useless or non-functional regions of mRNA are removed out, and the remaining segment is translated into Protein. By doing variations in coding region, we can obtain multiple proteins from a single nucleotide sequence. The same nucleotide sequence might contain exons of Protein 1 as well as Protein 2. When mRNA of Gene 1 is expressed, then the portion of nucleotides in Gene 2 are spliced/removed from the sequence. So only exons of Gene 1 will remain in mRNA and it'll be transcribed into Protein 1, due to change in reading frame of codons.

700 amino acids means 700 x 3 = 2100 nucleotides.

So 900 nucleotides will be spliced out from the mRNA sequence to get Protein 1

Similarly when Gene 2 is translated, the exons of Gene 1 will be removed. So due to change in reading frame of the codons, the mRNA sequence coding for Protein 2 will be translated.

310 amino acid means 310 x 3 = 930 nucleotides.

So 2070 different nucleotides will be spliced out from the mRNA sequence to get Protein 2.

You may go through Alternate Splicing in detail, if you want further clarification over this topic.

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