Genetic Code

The genetic code is a triplet code, meaning that each set of three nucleotides, or codon, along the sequence of an mRNA molecule is translated into one amino acid. The codons shown on this table are almost universal, and are used in protein synthesis by nearly all organisms, from bacteria to humans. For example, the mRNA nucleotide sequence AUG is translated into methionine, GCU is translated into alanine, and so on. Since 64 different codons are possible, but only 20 amino acids exist, some amino acids are represented by more than one nucleotide sequence. The methionine codon AUG is most often responsible for initiation of protein synthesis, while translation is usually terminated by the codons UAG, UAA, or UGA. To identify the amino acid coded by a particular nucleotide sequence using this chart, first choose the letter from the left-hand flashing box that represents the first base of the codon. Then choose the second base from the top flashing box and find the white box that lines up with both letters. Finally, choose the third base from the set of letters in the right-hand flashing box that lines up with the white box and match your codon to the correct amino acid.

Question 1: In 1968, the Nobel Prize in Physiology or Medicine was awarded jointly to Har Gobind Khorana, Robert W. Holley, and Marshall W. Nirenberg "for their interpretation of the genetic code and its function in protein synthesis" – in other words – for cracking the genetic code. What is the triplet of nucleotides coding for an amino acid called?
  1. A triple nucleotide.
  2. A trinucleotide.
  3. Base triplet.
  4. A codon.


Answer 1 Answer – (d) codon

Question 2: A total of 20 amino acids are redundantly translated from ____________- different combinations of nucleotides forming codons.
  1. 9
  2. 32
  3. 49
  4. 64


Answer 2 Answer – (d) 64

Question 3: Methionine is the translation product of the start codon for protein sequences and the translation is terminated one of the three following stop codons: ___________, ____________, or _____________?
  1. AAC, AAG, and AAT
  2. TAA, TAG, and TGA
  3. UAA, UAG, and UGA
  4. ATG, AAA, and UAA


Answer 3 Answer – (c) UAA, UAG, and UGA