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The four key macromolecules required for the sustenance of life are:

• Carbohydrates are the major source of energy for the cell and provide structural support.
• Lipids act as energy storage molecules, components of the plasma membrane, signaling molecules, and hormones.
• Proteins repair body tissues, produce hormones and enzymes required for carrying out important functions.
• Nucleic acids store and transfer genetic information from parents to offspring. DNA directs RNA synthesis which in turn is responsible for protein synthesis. Carbohydrates, proteins, and nucleic acids are repetitions of monomer units; however, the building blocks for lipids are fatty acids and glycerol.

Nucleotides are building blocks for nucleic acids such as DNA and RNA. They consist of a pentose sugar, nitrogenous base, and phosphate group. Nucleotides are joined by covalent bonds that form between the phosphate group of one nucleotide and the pentose sugar of the next nucleotide. Hence, option a is incorrect.

A disaccharide is a carbohydrate that is composed of two sugar monomers joined by glycosidic linkage. Lactose and maltose are examples of disaccharides. Hence, option b is incorrect.

Chaperones are proteins that stabilize the unfolded protein and assist in correct protein folding and assembly. For example, heat shock protein-70 (HSP-70) is a chaperone that attaches to newly synthesized proteins and protects them from other proteins that may bind and hinder the folding process. Hence, option d is incorrect.

Amino acids are the building blocks of proteins. Amino acids consist of a central carbon atom that is linked to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain. Amino acids join together to form a polypeptide by peptide bonds formed between the amino group of one amino acid and the carboxyl group of the neighboring amino acid. This polypeptide chain folds into its specific conformation that will enable it to fully function in the cell. Hence, option b is correct.