The mRNA sequence 5 UUCCUUAUGCGAUCGAUCGCAAACGUACGCCUUACCUAAC

The mRNA sequence

5\' UUCCUUAUGCGAUCGAUCGCAAACGUACGCCUUACCUAACG 3\'

Why are 10 amino acids encoded by the gene and not 11?

Also why is the promoter located to the left of the gene.

Solution

5\' UUC CUU AUG CGA UCG AUC GCA AAC GUA CGC CUU ACC UAA CG 3\'

The above nucleotides are divided into group of 3 nucleotides forming a codon. There are 13 codons, the initiation codon is AUG present at the third position. So the total number of amino acids encoded by the gene here are 10 and not 11 as UAA is the termination codon present at eleventh position.

The 5\' end is known as phosphoryl end(amino end) and 3\' end is known as hydroxyl end. This is the direction in which all mRNAs are read and synthesis of polypeptide chains occur.There are only 4 bases and 20 amino acids. Experiments have proved that three bases or nucleotides makes one codon and are required to encode 1 amino acid. An amino acid can be encoded by more than 1 codon. This is known as the degeneracy of genetic code which puts the codon into \"families\" and \"pairs\".There are 9 codon groups where the position of first 2 nucleotides specify a particular amino acid encoded by any nucleotide at the third position. These nucleotides pairs consists of 9 codon families. In the same way there are 13 codon pairs. Many a times an error can occur while copying a genetic code due to which there may be an increase or decrease in the formation of polypeptide chains and in turn change the structure and sequence of amino acids encoded by a gene.

The promoters are DNA sequences present in the 5\' region adjacent to the site where transcription begins. These promoters bind with RNA polymerase and transcription factors to start the process of mRNA transcript. At this site interaction of proteins with promoters take place to decide whether to activate or repress a gene activity. It is always present in the left side because as we have read above the translation will proceed from 5\' end to 3\' end.