Chapter 19, Problem 19.1CC

Suppose a tRNA has the anticodon 3′-CGU-5′. What two different codons could it bind to? How many different amino acids could this tRNA insert into a polypeptide?

Summary Introduction

To determine: The two different codons that will bind to the 3ʹ-CGU-5ʹ anticodon of tRNA.

Introduction: A codon is a sequence comprising of three nitrogenous bases that is present on the mRNA. Anticodon can be defined as three nitrogenous base sequences on the tRNA. The anticodon present on the tRNA pairs with the codon on mRNA.

Explanation of Solution

The anticodons are to bind along with the codons for an amino acid to be inserted into the polypeptide. The polarity of anticodons is opposite to that of the codons. For binding the following base substitutions occur:

• cytosine to guanine
• guanine to cytosine
• adenine to uracil
• uracil to adenine

According to this, one of the codon is 5ʹ-GCA-3ʹ.

The second codon can be determined by the wobble effect. According to the wobble effect in every codon coding for a particular amino acid, the first two nucleotides tend to be similar. Only the third nucleotide of codon shows variation. So going by this effect the other codon will be 5ʹ-GCG-3ʹ.

Hence, the two different codons that will bind to the 3ʹ-CGU-5ʹ anticodon of tRNA are 5ʹ-GCA-3ʹ and 5ʹ-GCG-3.

Summary Introduction

To determine: The different amino acid that could be inserted in the polypeptide by the tRNA.

Introduction: A codon is a sequence comprising of three nitrogenous bases that is present on the mRNA. Anticodon can be defined as three nitrogenous base sequence on the tRNA. The anticodon present on the tRNA pairs with the codon on mRNA.

Explanation of Solution

For an amino acid to be inserted into the polypeptide, the binding has to occur between the anticodons on tRNA with codons on the mRNA. The two different codons that will be binding to the 3ʹ-CGU-5ʹ anticodon are 5ʹ-GCA-3ʹ and 5ʹ-GCG-3. According to the data the codons GCA and GCG code for the amino acid alanine. The tRNA brings the amino acid alanine into the polypeptide.

Hence, the amino acid that could be inserted in the polypeptide by the tRNA is Alanine.