Which feature of the phosphodiester bond contributes most to the overall negative charge of the DNA molecule?

Correct option is A

The correct answer is (A) The phosphate group’s ionisable oxygen atoms

Explanation:

• The phosphodiester bond in DNA links the phosphate group of one nucleotide to the sugar of the next nucleotide, forming the backbone of the DNA strand.
• The phosphate group in this bond has ionizable oxygen atoms that can form negatively charged ions (as the oxygen atoms can lose a hydrogen ion, leaving a negatively charged oxygen).
• This negative charge from the phosphate groups contributes significantly to the overall negative charge of the DNA molecule.
• The ionizable oxygen atoms are key in making the DNA molecule negatively charged at physiological pH, which plays a critical role in its interaction with proteins and other molecules.

Information Booster:

• The phosphate group contains a phosphorus atom bonded to four oxygen atoms, three of which are negatively charged in the ionic form.
• This negative charge is crucial for the structure of DNA and affects how it interacts with other molecules, such as histones and proteins in the nucleus.

Additional Knowledge:
(B) The ribose sugar:

• While the ribose sugar (in RNA) or deoxyribose sugar (in DNA) is an essential component of the nucleotide, it does not contribute to the negative charge of the DNA. The sugar’s role is mainly structural.

(C) The methyl group of thymine:

• The methyl group of thymine is part of the base but does not contribute to the overall negative charge of the DNA. It plays a role in DNA methylation and gene expression regulation, but not in the charge.

(D) The nitrogen in purines:

• The nitrogen atoms in purines (adenine and guanine) are part of the base structure and participate in hydrogen bonding with complementary bases. They do not contribute to the negative charge of the DNA molecule.