Genetic Code

The nucleotides build up the double helix DNA. The two strands of the DNA are bonded to one another with the help of hydrogen bonds. The adenine of one strand and thymine of another strand are bonded with hydrogen bonds. The hydrogen bonds are also seen between the cytosine and guanine bases of the two strands. It means that the adenine and thymine residues are same in number in a double helix while the guanine and cytosine residues will also be same in number. In the RNA, the sugar moiety is ribose and uracil is seen in the place of thymine.

In a protein or polypeptide,the amino acids are linked with each other with the aid of peptide bond. A peptide bond is formed when the amino end of an amino acid combines with the carboxyl end of the adjacent amino acid. In the process a water molecule is eliminated. The monosaccharides combine with a glycosidic bond to form a polysaccharide. This bond is also formed resulting in dehydration. In a nucleic acid, the one end of the phosphate molecule joins with the 5’carbon of one sugar and 3’carbon of another sugar molecule. The link between the phosphate molecule and the sugar molecule is formed due to an ester bond. Hence, phospho diester bond is formed.

The functional part of the genome or the region in the genome that codes for a protein is called as a gene. The protein-coding genes are known to be consisting of tri-nucleotide regions called codons, each of them coding for an amino acid. The nucleotide comprises of one of the four nitrogen bases, phosphate group and a deoxyribose sugar molecule. The purines guanine and adenine are bigger in size and comprise of two Aromatic rings. Thymine and cytosine are pyrimidines that are smaller in size and they comprise of one aromatic ring.

Every organism has DNA specific to that organism. Genetic code is a nucleotide sequence which helps in the transfer of information from DNA to RNA and further to the protein. There are certain rules that are offered by the genetic code that helps in the conversion of information present in the DNA of the living cells, into proteins. The genetic code aids in matching the nucleotide sequences of the codons and amino acids. The tri-nucleotide sequence of the nucleic acid identifies with one amino acid. Most of the genes are coded by the same genetic code and hence the referred genetic code is called as standard or canonical genetic code. The standard genetic code is also called simply as genetic code although there are other variations of genetic codes. Therefore, the canonical genetic code is not worldwide. In the case of mitochondria in humans, the synthesis of proteins depends on the genetic code which is different from the canonical genetic code. The source of the genetic code in the genome of an organism exists in DNA while it exists in RNA in the case of some viruses.

The codon comprising of three nucleotides constitute the genetic code. As there are four nitrogen bases, the codon can form 64 different combinations. All these codon possibilities were found to be representing 20 aminoacids. The DNA is transcribed into messenger RNA which represents the basis for the protein formation. The transfer RNA further recognizes the codons of the mRNA and translates them into aminoacids that are useful in the systematic synthesis of protein.