Chapter 21, Problem 21.40E

Which of the following statements about the genetic code are true and which are false? Correct each false statement.

a. Each codon is composed of four bases.

b. Some amino acids are represented by more than one carbon.

c. All codons represent an amino acid.

d. Each living species is thought to have its own unique genetic code.

e. The codon AUG at the beginning of a sequence is a signal for protein synthesis to begin at that codon.

f. It is not known if the code contains stop signals for protein synthesis.

Interpretation Introduction

(a)

Interpretation:

The statement about genetic code that each codon is composed of four bases is true or false is to be predicted. The correct statement is to be stated.

Concept introduction:

The three nitrogenous bases present on messenger RNA which corresponds to specific amino acid are known as codon. The three nitrogenous bases present on transfer RNA which are complementary to three nitrogenous bases present on messenger RNA are known as anticodon.

Answer to Problem 21.40E

The statement about genetic code that each codon is composed of four bases is false. The correct statement is that each codon is composed for three bases.

Explanation of Solution

The three nitrogenous bases present on messenger RNA which corresponds to a specific amino acid are known as codon. Therefore, it is false that each codon is composed of four bases. The correct statement is that each codon is composed for three bases.

Conclusion

The statement about genetic code that each codon is composed of four bases is false. The correct statement is that each codon is composed for three bases.

Interpretation Introduction

(b)

Interpretation:

The statement about genetic code that some amino acids are represented by more than one codon is true or false is to be predicted. The correct statement is to be stated.

Concept introduction:

The three nitrogenous bases present on messenger RNA which corresponds to specific amino acid are known as codon. The three nitrogenous bases present on transfer RNA which are complementary to three nitrogenous bases present on messenger RNA are known as anticodon.

Answer to Problem 21.40E

The statement about genetic code that some amino acids are represented by more than one codon is true.

Explanation of Solution

The three nitrogenous bases present on messenger RNA which corresponds to a specific amino acid are known as codon. It is true that some amino acids are represented by more than one codon. For example, amino acid alanine is represented by four different codons GCA, GCC, GCG and GCU.

Conclusion

The statement about genetic code that some amino acids are represented by more than one codon is true.

Interpretation Introduction

(c)

Interpretation:

The statement about genetic code that all codons represent an amino acid is true or false is to be predicted. The correct statement is to be stated.

Concept introduction:

The three nitrogenous bases present on messenger RNA which corresponds to specific amino acid are known as codon. The three nitrogenous bases present on transfer RNA which are complementary to three nitrogenous bases present on messenger RNA are known as anticodon.

Answer to Problem 21.40E

The statement about genetic code that all codons represent an amino acid is false. Out of $64$ codons, $61$ codons represent an amino acid.

Explanation of Solution

The three nitrogenous bases present on messenger RNA which corresponds to a specific amino acid are known as codon. However, codons UAG, UAA and UGA do not correspond to any amino acid. They represent a stop signal during the synthesis of protein.

The total number of codons is $64$ out of which three codons do not represent any amino acid. Therefore, out of $64$ codons, $61$ codons represent an amino acid.

Conclusion

The statement about genetic code that all codons represent an amino acid is false. Out of $64$ codons, $61$ codons represent an amino acid.

Interpretation Introduction

(d)

Interpretation:

The statement about genetic code that each living species has its own unique genetic code is true or false is to be predicted. The correct statement is to be stated.

Concept introduction:

The three nitrogenous bases present on messenger RNA which corresponds to specific amino acid are known as codon. The three nitrogenous bases present on transfer RNA which are complementary to three nitrogenous bases present on messenger RNA are known as anticodon.

Answer to Problem 21.40E

The statement about genetic code that each living species has its own unique genetic code is false. The correct statement is that each living species contains same genetic codes but in a different sequence.

Explanation of Solution

The genetic codes present in each of the living species are the same; however, the arrangement of these genetic codes is different in each species. Therefore, the statement about genetic code that each living species has its own unique genetic code is false. The correct statement is that each living species contains same genetic codes but in a different sequence.

Conclusion

The statement about genetic code that each living species has its own unique genetic code is false. The correct statement is that each living species contains same genetic codes but in a different sequence.

Interpretation Introduction

(e)

Interpretation:

The statement about genetic code that codon AUG at the beginning of a sequence is a signal for protein synthesis to begin at that code is true or false is to be predicted. The correct statement is to be stated.

Concept introduction:

The three nitrogenous bases present on messenger RNA which corresponds to specific amino acid are known as codon. The three nitrogenous bases present on transfer RNA which are complementary to three nitrogenous bases present on messenger RNA are known as anticodon.

Answer to Problem 21.40E

The statement about genetic code that codon AUG at the beginning of a sequence is a signal for protein synthesis to begin at that code is true.

Explanation of Solution

The triplet code that represents the start of the signal during translation is AUG. Therefore, the statement about genetic code that codon AUG at the beginning of a sequence is a signal for protein synthesis to begin at that code is true.

Conclusion

The statement about genetic code that codon AUG at the beginning of a sequence is a signal for protein synthesis to begin at that code is true.

Interpretation Introduction

(f)

Interpretation:

The statement about genetic code that in a protein synthesis the code contains stop signals is not known is true or false is to be predicted. The correct statement is to be stated.

Concept introduction:

The three nitrogenous bases present on messenger RNA which corresponds to specific amino acid are known as codon. The three nitrogenous bases present on transfer RNA which are complementary to three nitrogenous bases present on messenger RNA are known as anticodon.

Answer to Problem 21.40E

The statement about genetic code that in a protein synthesis the code contains stop signals is not known is false. The correct statement is that three codons are represented as a stop signal in the protein synthesis.

Explanation of Solution

The triplet codes that correspond to the stop signals are UAG, UAA and UGA. If the code contains UAG, UAA or UGA, the synthesis of protein stops. Therefore, the statement about genetic code that in a protein synthesis the code contains stop signals is not known is false. The correct statement is that three codons are represented as a stop signal in the protein synthesis.

Conclusion

The statement about genetic code that in a protein synthesis the code contains stop signal is not known is false. The correct statement is that three codons are represented as a stop signal in the protein synthesis.