Molecular structure : Molecules have fixed equilibrium geometries--bond lengths and angles--that are dictated by the laws of quantum mechanics. The chemical formula and the structure of a molecule are the two most important factors that determine its properties, particularly its reactivity. Structure also plays an important role in determining polarity, phase of matter, color, magnetism, and taste, among several other properties.
From: en.wikipedia.org/wiki/Molecular_structure

Molecular Biology
the branch of biology concerned with the structure and development of biological systems in terms of the biochemistry of their molecular components. Molecular biology overlaps a wide variety of other disciplines in use of molecular techniques eg PCR, RFLP analysis, etc.
From : www.accessexcellence.org/AE/AEC/CC/crick_glossary.html