The building blocks of nucleic acids are ________.

a. sugars

b. nitrogenous bases

c. peptides

d. nucleotides

Nucleotides are macromolecules that occur in two forms in nature: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most living organisms contain DNA as their genetic material that is transferred from parent to offspring. Some viruses contain RNA as their genetic material. DNA also gives instructions for protein synthesis needed for the functioning of the cells and tissues.

Sugars or carbohydrates are a class of macromolecules that are a major source of energy to the cell and provide structural support to plants, fungi, and arthropods. Glucose is the major source of energy for the cell. Glucose molecules are the building blocks for disaccharides and more complex molecules like polysaccharides. Hence, option a is incorrect.

Nitrogenous bases are one of the three parts of a nucleotide and consist of a nitrogen-containing ring structure. Nitrogenous bases are of two types: purines and pyrimidines. Purines consist of two carbon-nitrogen fused rings and pyrimidines consist of a single carbon-nitrogen ring. DNA nucleotides consist of purines - adenine (A) and guanine (G) and pyrimidines - cytosine (C) and thymine (T). RNA has A, G, and C but T is replaced by uracil (U). Hence, option b is incorrect.

Peptides are a short chain of amino acids, typically 2-50 amino acids long. Amino acids are the building blocks for the formation of peptides that are linked together by peptide bonds. Several hormones and antibiotics consist of peptides. Hence, option c is incorrect.

Nucleotides are the building blocks of nucleic acids - DNA and RNA. They consist of three parts: a nitrogenous base, pentose sugar, and a phosphate group. In DNA, the pentose sugar is deoxyribose and in RNA it is ribose.

The phosphate group of one nucleotide and the pentose sugar of the next nucleotide form a covalent bond, which binds the monomers together.

This phosphodiester linkage forms the sugar-phosphate backbone of the nucleic acids. Hence, option d is correct.