In: Biology
Human FAV gene's coding region is 7440 bp long however the produced protein is 680 amino acid long. What is the reason? Explain scientifically using NUMBERS.
Human Genome contains many genes. one of the important characteristic of human genes (eukaryotic genes) is that they have interspersed non coding sequences within their coding regions. These non coding regions are known as introns. As the coding regions of the genes get transcribed, the introns also get trancribed in the form of hnRNA. However the hnRNA undergoes posttranscriptional modifications which includes many events like addition of Poly A tail at the 3' end, 7-methyl guanosine cap at the 5' end, removal of introns and exon reshuffling. As far as the removal of introns or RNA splicing is concerned, the length of hnRNA is very much reduced and the mature mRNA so produced contains only coding regions reshuffled in a proper arrangement to code for a specific polypeptide. During translation or protein sythesis, the entire mRNA is not translated as some of the sequences are required for attachement of mRNA to ribosomal subunits, and that protein synthesis occurs at a specific codon and terminates at specific codons. Therefore it further reduces the length of polypeptide.
As provided in the question, The length of FAV gene's coding region is 7440 bp long.
The length of the polypeptide is 680 aminoacids. As we know one amino acid is coded by three nitrogenous bases, therefore 680 aminoacids will be coded by 680 x 3 = 2040 bases and one codon act as termination codon.
Hence the total number of bases that code for the polypeptide is 2043.
Therefore out of 7440 bp DNA sequence (coding region), only 2043 codes for the polypeptide and the rest bases represent introns and other regulatory sequences.