A sequence of how many nucleotides in messenger `RNA` makes a codon for amino acid ?

Options

A. Three
B. Four
C. One
D. Two

Answer

A

Explanation

One kind of `RNA` (called fittingly, messenger `RNA`) carries a message to the ribosome, where protein synthesis actually takes place. At the ribosome, messenger `RNA` calls up a series of transport `RNA` molecules, each of which is loaded with a particular amino acid, The order in which the transport `RNA` molecules are called by (i.e., the sequence in which the amino acid are built into the protein chain) depends upon the sequence of bases along the messenger `RNA` chain.
A sequence of three nucleotide in messenger `RNA` makes a codon for an amino acid because four bases in messenger `RNA` (i.e. adenine, cytosine, guanine and uracil) have been shown to act in the form triplet. Thus, `GAU` is the code for aspartic acid, `UUU`, phenylalanine, `GUG` valine. There are 64 three-letter code words (codons) and only 20-odd amino acids, so that more than one codon can call up the same amino acids: `CU U` and `CUG`, leucine, `GA A` and `GAG`, glutamic acid.