Question

The 64 Codons constitute genetic code because-
A) There were 64 types of amino acid.
B) 64 types of tRNA.
C) The genetic code is a triplet.
D) There are 64 enzymes.

Answer 1

The genetic code is the set of rules used by living cells to translate information encoded within genetic material i.e DNA or mRNA sequences of nucleotide or codons into various proteins. A single codon will code for the same/ single amino acid.

Complete answer:
Translation takes place in the ribosome, which links amino acids in a sequence that is directed by messenger RNA (mRNA). By using transfer RNA (tRNA) molecules to carry amino acids and read the mRNA three nucleotides at a time. The genetic code is highly similar among all organisms and can be expressed in a form of 64 codons.

According to the genetic code, three bases must be employed to encode the 20 standard amino acids (statement A is wrong) used by living cells to build the various proteins. With four different nucleotides, a code of 2 nucleotides would allow for only a maximum of 42 codons = 16 amino acids. A codon of 3 nucleotides could code for a maximum of 64 codons.

The codons specify which amino acid will be added next during protein synthesis in ribosomes. With few exceptions, a three-nucleotide codon in a nucleic acid sequence specifies a single amino acid. Translation starts with a start codon(AUG which codes for methionine). There are also 3 stop codons (UUA, UAG, UGA) to terminate the chain.

As a single tRNA will be available for one amino acid. So, there are 20 functional tRNAs. Enzymes are proteins that bring about the catalysis of a biological reaction. Proteins are the sequence of different amino acids. Thus, the genetic code expresses in such a way that 64 codons constitute it, as it occurs in triplets.

Thus the correct answer is option ‘C’.

Note: Translation is the process in which mRNA with the help of the enzyme decodes into the amino acid chain. The proteins are the sequence of the amino acid chain. The start codon alone is not enough to start the process, nearby sequences such as the Shine-Dalgarno sequence in E. coli and Kozak sequence in eukaryotes is required along with the initiation factor.