Question

What is not true for genetic code?
a. It is unambiguous.
b. A codon in mRNA is read in a non-contiguous fashion.
c. It is nearly universal.
d. It is degenerate.

Answer 1

Hint: As we know that genetic code is a group of combinations of three nucleotides which forms codon and that codes for amino acid. Genetic code is stored on any one strand of DNA as well as spread and non-overlapping nitrogenous base (Adenine, Guanine, Cytosine and Thymine) sequences. Genetic code consists of three lettered words known as codon and there are 64 such codons. During translation starting from the start codon (AUG) until it reaches to stop codon cells read them in mRNA from 5’ to 3’.

Complete answer:
Genetic code has an inter-relationship with DNA or mRNA sequence and amino acid sequence. mRNA sequence contains coded information for one amino acid and three nucleotides.
Codon is a triplet of nucleotide bases forming 64 codons and each codes for 1 amino acid out of 20( Glutamic acid, Methionine, Phenylalanine, Serine, Tryptophan, Tyrosine, etc.).
Option (a)- Genetic code is unambiguous because each codon codes for only one amino acid and therefore there is no complexion during translation. Example; AUG codes for only Methionine i.e. amino acid.
Option(b)- A codon in mRNA is read in a non-contiguous fashion; this statement is incorrect because it is read in contiguous fashion as there is no punctuation in between i.e. codons do not contains any space in between or there is no punctuation between two or more codons.
Option(c)- It is nearly universal because the basic four nucleotides form the base of DNA in all organisms and also forms genetic codes that code for the same amino acids in all the organisms.
Option(d)- It is degenerate because one amino acid is coded by more than one codon as the amino acids Arginine, Alanine and Leucine contain six same codons. There are two types of degeneracy: 1. Partial and 2. Complete.

Hence, Option (b) i.e. A codon in mRNA is read in a non-contiguous fashion is the correct answer as it is not a true statement for genetic code.

Note: Each codon is made of three nitrogenous bases, do not overlap other codons and are independent. Codons in mRNA are read in continuous or contiguous fashion. Genetic code is important in translation as it determines the amino acid so that the protein structure is decided.