Molecular biology is the branch of biology that deals with the structure and function of the macromolecules e.g. proteins and nucleic acids or the study of biology at a molecular level. The branch overlaps with another area of biological study particularly genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell, including the interrelationship of DNA, RNA and protein synthesis and learning how these interactions are regulated. Atom and molecule are the fundamental units for all matters in the universe.
Molecular physics is the study of the properties, dynamics and interactions of the basic (but not fundamental) building blocks of matter. Various types of spectroscopy technique used to study chemical bonds between atoms as well as the molecular dynamics. The field is closely related to atomic physics and overlaps greatly with theoretical chemistry, physical chemistry, and chemical physics.