THE MOLECULAR BASIS OF INHERITANCE
STRUCTURE OF NUCLEIC ACIDS
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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the four nucleic acid bases combine in three letter sequences that each define an amino acid
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the four nucleic acid bases combine in two letter sequences that each define an amino acid
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the four nucleic acid bases are converted into tRNA molecules which can each attach to sixteen different amino acids
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the four bases each specify one amino acid, and these then combine to form the other sixteen amino acids
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Detailed explanation-1: -How do the four different nucleotides found in DNA result in twenty different amino acids that are then used to form proteins in the cell? The four nucleic acid bases combine in 3 letter sequences to make an amino acid.
Detailed explanation-2: -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.
Detailed explanation-3: -Since each of the 20 amino acids is chemically distinct and each can, in principle, occur at any position in a protein chain, there are 20 × 20 × 20 × 20 = 160, 000 different possible polypeptide chains four amino acids long, or 20n different possible polypeptide chains n amino acids long.
Detailed explanation-4: -11. How can only four bases in RNA carry instructions for 20 different amino acids? The genetic code is read three letters at a time, so that each “word” of the coded message is three bases long. that is to be added to a polypeptide.