Which atoms were these molecules made up of and in what relative proportions? which of these atoms plays a central role as the "backbone" to the structure of these atoms? why do you suppose this is?

The key repeating units in these macromolecules are: sugar (aldose/ketose) for carbohydrates, amino acids for proteins, fatty acids and CoA for lipids and a nitrogenous base, sugar and phosphate for nucleic acids.

What is the composition of these macromolecules?

Carbohydrates contain only the elements carbon, hydrogen and oxygen (CH2O), and their combustion will yield carbon dioxide plus one or more molecules of water.
Proteins contain the elements carbon, hydrogen, and oxygen, and nitrogen. In each amino acid the elements are arranged into a specific conformation around a carbon center.
Lipids are composed of carbon, hydrogen and oxygen atoms, and in some cases contain phosphorus, nitrogen, sulfur and other elements.
Nucleic acids contain the same elements as proteins: carbon, hydrogen, oxygen, nitrogen and phosphorous (C, H, O, N, and P).
Carbon is the key element which serves as the basic structural component, or “backbone,” of the macromolecules.
It has unique properties that allow it to form covalent bonds to as many as four different atoms.
Carbon is unique in its ability to form large, diverse molecules.

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Question: Consider the structure of biologically important macromolecules (i.e. carbohydrates, proteins, lipids, and nucleic acids) and explain the significance of the key elements involved in formation of these molecules. Which atoms were these molecules made up of and in what relative proportions? Which of these atoms plays a central role as the "backbone' to the structure of these atoms? Why do you suppose this is?