THE MOLECULAR BASIS OF INHERITANCE
STRUCTURE OF NUCLEIC ACIDS
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[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Detailed explanation-1: -There are 64 possible codons, three of which do not code for amino acids but indicate the end of a protein. The remaining 61 codons specify the 20 amino acids that make up proteins. The AUG codon, in addition to coding for methionine, is found at the beginning of every mRNA and indicates the start of a protein.
Detailed explanation-2: -The four types of nitrogen bases found in nucleotides are: adenine (A), thymine (T), guanine (G) and cytosine (C). The order, or sequence, of these bases determines what biological instructions are contained in a strand of DNA.
Detailed explanation-3: -1. Three is the minimum number of nucleotides per codon needed to encode 20 amino acids. 4x4 = 16 amino acids. (i.e. 64 different combinations of four nucleotides taken three at a time).
Detailed explanation-4: -In fact, even two nucleotides per amino acid (a doublet code) could not account for 20 amino acids (with four bases and a doublet code, there would only be 16 possible combinations [42 = 16]). Thus, the smallest combination of four bases that could encode all 20 amino acids would be a triplet code.