Question Video: Identifying the Incorrect Statement about the Genetic Code | Nagwa Question Video: Identifying the Incorrect Statement about the Genetic Code | Nagwa

Question Video: Identifying the Incorrect Statement about the Genetic Code Biology • Third Year of Secondary School

Which of these statements is not true about the standard amino acids that belong to the genetic code? [A] Each amino acid contains a codon of three nucleotides in its structure. [B] Amino acids are sometimes coded by several codons in the genetic code. [C] A sequence of amino acids forms a polypeptide, which forms a protein. [D] There are twenty amino acids in the standard genetic code.

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Video Transcript

Which of these statements is not true about the standard amino acids that belong to the genetic code? (A) Each amino acid contains a codon of three nucleotides in its structure. (B) Amino acids are sometimes coded by several codons in the genetic code. (C) A sequence of amino acids forms a polypeptide, which forms a protein. (D) There are 20 amino acids in the standard genetic code.

In order for a gene in DNA to be converted into a protein, it needs to go through two steps. First, the DNA sequence is converted into mRNA during a process called transcription. Then, the sequence of mRNA is converted into a sequence of amino acids to form a polypeptide during translation. This polypeptide can then fold to form a protein. So, answer choice (C) is a correct statement about amino acids and therefore is incorrect.

Let’s look at how a sequence of mRNA can be translated into amino acids. A group of three nucleotides in mRNA is called a codon. In this nine-nucleotide sequence of mRNA, there’s three codons. The specific sequence in a codon corresponds to a specific amino acid. The sequence AGG corresponds to the amino acid arginine.

To determine what codon codes for which amino acid, we can use a codon wheel as shown here. Here, we can see that codon AGG corresponds to arginine. However, the codon AGA also corresponds to arginine. This is because the genetic code is redundant, or degenerate, and amino acids are sometimes coded by several codons. So, answer choice (B) is a correct statement and is, therefore, incorrect.

Also, there are 20 amino acids in the standard genetic code. So, answer choice (D) is a correct statement and is, therefore, incorrect.

The incorrect statement is given by answer choice (A). Amino acids do not contain nucleotides in their structure. mRNA contains codons which are made up of three nucleotides. Therefore, the correct answer is (A). Each amino acid contains a codon of three nucleotides in its structure.

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