• The code is unambiguous which suggests that code is for only one amino acid.
• There is no comma, gap in the code.
• The code is degenerate. This means that one amino acid has more than one codon. For example phenylalanine is specific to two codons UUU and UUC. Only tryptophan and methionine are coded by single codon.
• The codon is non-overlapping. For example a code as AUGCUGGGUGAUUUUGUA then codons will be AUG, CUG, GGU and so on and not AUG, UGC, GCU and so on.
• Genetic code is universal, which suggests that genetic code and its meaning is common for all life forms. However there are some exceptions to this rule. For example, UGA is a stop codon but it codes for tryptophan in Mycoplasma, Spiroplasma, and mitochondria of several species. Similarly, CUG codes for Leucine in general but in yeast mitochondria it codes for threonine.

The basic process that occurs in protein synthesis is the formation of a peptide bond  between the carboxyl group of one amino acid at the end of growing polypeptide and a free amino group on an amino acid. Peptide synthesis requires several components- mRNA, tRNAs, Ribosomes and several factors and enymes for conducting the process.

Messenger RNA (mRNA) : mRNA has a 5’ end, 5’ UTR, ribosomal binding site, coding sequence, 3’ UTR. In eukaryotes there are additional structures as 5’ Guanine cap and poly (A) tail (detail already discussed in earlier lecture) Figure 30.2.  Messenger RNA (mRNA) has 3 reading frames out of which only one codes for desired protein. If in the sequence of bases there is no stop codon to interrupt the translation then that synthesis entire polypeptide chain and is that is called as open reading frames (ORF).

Figure 30.2 :Structure of m RNA