Which bond connects two amino acids?

Which of the following compounds shows aromatic properties?

Select the correct match for $X$ and $Y$:

Column $X$	Column $Y$
$(1)$ Primary protein	$(P)$ Globular or fibrous form
$(2)$ Secondary protein	$(Q)$ Three-dimensional arrangement of a single polypeptide chain
$(3)$ Tertiary protein	$(R)$ Gene-controlled
$(4)$ Quaternary protein	$(S)$ Helical or pleated sheet form

Which one of the following is most essential for the growth and formation of new cells?

Primary proteins are also called as polypeptides because:

Schematically represent primary, secondary and tertiary structures of a hypothetical polymer, for example, a protein.