Question

Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together. What would happen to DNA molecules treated with these enzymes?

(A) The two strands of the double helix would separate.

(B) The phosphodiester linkages of the polynucleotide backbone would be broken.

(C) The pyrimidines would be separated from the deoxyribose sugars.

(D) All bases would be separated from the deoxyribose sugars.

Short answer

(A) The statement “The two strands of the double helix would separate.” is false.

(B) The statement “The phosphodiester linkages of the polynucleotide backbone would be broken.” is true.

(C) The statement“The pyrimidines would be separated from the deoxyribose sugars.” is false.

(D) The statement “All bases would be separated from the deoxyribose sugars.”is false.

Step-by-step solution

Structure of DNA

DNA is deoxyribonucleic acid. It is a double-stranded structure made up of polynucleotide chains interwind around each other.Each nucleotide in the polynucleotide chain is attached by covalent bonds between the sugar of one nucleotide and the phosphate bond of the next nucleotide.

This results in a sugar-phosphate backbone. According to the base-pairing rule, the nitrogenous bases are joined together by hydrogen bonds where purine in the first chain binds to a pyrimidine base in the complementary chain. Accordingly, adenine binds to thymine (A—T) while cytosine binds to guanine (G—C).

Explanation of option ‘(A)’

Hydrogen bonds join the two strands of double helix through the nitrogenous bases. The enzyme used is known to catalyze the hydrolysis of covalent bonds.

Thus, the two strands of DNA double helix are do not separate.

Therefore, the given statement is false.

Explanation of option ‘(B)’

The nucleotides in each chain of DNA double helix are joined by a covalent bond called the phosphodiester linkage. The enzyme hydrolyzes this linkage.

Thus, thephosphodiester linkages of the polynucleotide backbone would be broken by the enzyme.

Therefore, the given statement is true.

Explanation of option ‘(C)’

The bond between the deoxyribose sugar and pyrimidine base is a glycosidic bond. C1 of sugar is bonded to N1 of pyrimidine.

Thus, the enzyme cannot break the bond between pyrimidine and deoxyribose sugar.

Therefore, the given statement is false.

Explanation of option ‘(D)’

The bases of the deoxyribose sugars are bonded to each other by glycosidic bonds. The enzyme used to treat DNA molecules break the covalent bonds.

Thus, the bases would not separate from the deoxyribose sugars by the action of the enzyme.

Therefore, the given statement is false.