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Chapter 17: Q17-2TYU (page 362)

Which of the following is not true of a codon?

  1. It may code for the same amino acid as another codon.

  2. It never codes for more than one amino acid.

  3. It extends from one end of a tRNA molecule

  4. It is the basic unit of the genetic code.

Short Answer

Expert verified

  1. The statement “It may code for the same amino acid as another codon” isfalse.

  2. The statement “It never codes for more than one amino acid” isfalse.

  3. The statement “It extends from one end of a tRNA molecule” is true.

  4. The statement “It is the basic unit of the genetic code” is false.

Step by step solution

01

Codon

An mRNA (messenger ribonucleic acid) molecule is a sequence of nucleotides transcribed from the nucleotides present in the DNA (deoxyribonucleic acid). A series of three-nucleotide sequences of mRNA that code for specific amino acids are called codons.

02

Explanation of option (A)

Many codons can code for the same amino acid. This is called the degeneracy of the genetic code. For example, GAG and GAA are two codons that code for glutamic acid.

Thus, a codon that codes a specific amino acid can also be coded by another codon.

Therefore, the given statement is false.

03

Explanation of option (B)

A codon codes for a single amino acid, but an amino acid can be coded by more than one codon. For example, GAG only codes for glutamic acid, but glutamic acid is coded by two codons (GAG and GAA).

Thus, codon codes for a single amino acid.

Therefore, the given statement is false.

04

Explanation of option (C)

Codon is the triplet nucleotide sequence on mRNA. However, one end of the tRNA contains the amino acid coded by the mRNA codon.

Thus, the tRNA molecule does not contain a codon.

Therefore, the given statement is true.

05

Explanation of option (D)

The sequence of nucleotides on the RNA molecule that specifies the amino acids of the polypeptide chain is referred to as the genetic code. The mRNA codon codes for the amino acid.

Thus, the codon is the basic unit of the genetic code.

Therefore, the given statement is false.

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Most popular questions from this chapter

What enables RNA polymerase to start transcribing a gene at the right place on the DNA in a bacterial cell? In a eukaryotic cell?

The height of a stack letters in a logo indicates the predictive power of the stack (determined statistically). If the stack is tall, we can be more confident in predicting what base will be in that position of a new sequence is added to the logo. For example, at position2 in the sequence alignment, all 10 sequences have a G: the probability of finding a G there in a new sequence is very high, as is the stack in the sequence logo. For short stacks, the bases all have about the same frequency, so it’s hard to predict would be at those positions. (a) Looking at the sequence logo, which two positions have the most predictable bases? What bases do you predict would be at those positions in a newly sequenced gene? (b) Which 12 positions have the least predictable bases? How do you know? How does this reflect the relative frequencies of the base shown at these positions in the sequence alignment? Use the two leftmost positions of the 12 as examples in your answer.

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