2. The following figure represents the primary transcript of a typical eukaryoti

Question

2. The following figure represents the primary transcript of a typical eukaryotic protein-coding gene: Exon 1 Intron 1 Exon 2 Intron 2Exon 3 bp 120 75 60 70 30 Poly (A) What is the size in bases of the fully processed, residues in your calculations. This primary transcript is responsible for the production of a 50 amino acid protein in the liver and a 60 amino acid protein in the brain. Explain how this is possible a. mature mRNA? Assume a poly (A) tail of 200 adenine b. 1 The coding sequence for gene F is read from left to right. The coding sequence for gene G is read from right to left. Which strand of DNA serves as the template for transcription of each gene? stranGene f 5' 3' Gene G 5' 4 In prokaryotes, a search for genes in a DNA sequence involves scanning the DNA sequence for long open reading frames What problem would there be with this approach in eukaryotes? 5. What do the processes of DNA synthesis, RNA synthesis and polypeptide synthesis have in common?

Explanation / Answer

2.a. Since mRNA includes introns and exons both and undergoes splicing to yield mature mRNA which does not include introns, the above mRNA's length in base pairs can be calculated by using only exon length and poly(A) tail.

So length of mature mRNA would be 120+60+30 (corresponding to the exon lengths) + 200 (poly A tail)

Which is 410bp.

b. A primary transcript can yield proteins of different length, example as mentioned , 50 amino acid in liver or 60 amino acid in brain because of differential splicing in different tissues. Various cic-acting elements like regulatory sequences of promoters or trans acting elements like different transcription factors also play a role in differential splicing. If the same primary transcript has different regions of exons and introns, then splicing pattern would differ and hence the length of the mature transcript which codes for the proteins.This is process is known as alternative splicing and helps in controlling gene expression and production of tissue specific mRNA and protein isoforms.

1. The coding sequence of Gene F is read from 5' to 3'. Coding sequence is from the strand that is mRNA like strand and has corresponding same bases as in mRNA.The template strand produces the complementary sequence (of the coding strand). For gene F , strand 2 is template strand and coding strand is strand 1, 5' to 3' direction since it is left to right.

In a similar way, for Gene G, coding strand is strand 2 (right to left or 5' to 3' ) and template strand is strand 1.

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