Q.Sugar, amino acids and nucleotides unite to their respective subunits to form --------

A living cell's chemistry is built almost entirely from just a handful of elements — the prime elements carbon, hydrogen and oxygen (drawn largely from air and water), the macro elements nitrogen, phosphorus, potassium, calcium, magnesium and sulfur, and a set of trace elements (boron, chlorine, zinc, copper, iron, sodium, molybdenum, nickel, silicon, cobalt) needed only in minute amounts. The chemical substances built from these elements inside the cell's protoplasm are collectively called biomolecules, and are broadly classed as organic (carbon-containing: macromolecules and micromolecules) or inorganic (the mineral elements themselves).

Chemically, every living organism is built around three basic types of macromolecules — large polymer molecules assembled by joining together many smaller, repeating subunits called monomers:

• Polysaccharides (carbohydrates) are polymers of monosaccharides.
• Polypeptides (proteins) are polymers of amino acids.
• Polynucleotides (nucleic acids) are polymers of nucleotides.

Alongside these, the cell also contains lipids (water-insoluble, comparatively small molecules, not built as monomer-chain polymers) and secondary metabolites (small organic molecules such as alkaloids, phenolics and terpenoids that are not essential for basic growth but serve specialised roles). Biochemistry is the branch of biology that studies this chemistry of living systems — the molecular basis of cell communication, inheritance, and disease.