Bronies Coklat

Although names like Molecular Biology and Biochemistry are used in a fairly consistent manner, it is not always clear to outsiders what the primary concerns of a Molecular Biologist are, and how they differ from those of a Biochemist.
Let's take an arbitrary metabolic reaction occurring in a cell, catalyzed by an enzyme.
A molecular biologist would want to know how the gene that expresses this enzyme is controlled: when is it expressed, what are the factors that turn its expression on and off? Is the enzyme stable once it has been generated, or does it rapidly break down in the cell? The relevant points of interest are the signals that control the presence of the enzyme in the cell, how the activity of this enzyme is controlled and balanced in the cell with respect to all the other processes that are occurring around it in the cell, or perhaps before and after its expression during the lifetime of the cell.
A biochemist would be more interested in the role the enzyme plays in facilitating the reaction - the relative free energy of the reactants and products, and how the transition state is stabilized by the interactions between the reactants and the interior of the enzyme. In this case, the balance of energy between reactants and products, and the overall change in the kinetics of the reaction.
So a molecular biologist is most interested in how all the critical processes required for cell function are regulated, and how the available nutrients and energy are apportioned among them. A biochemist is more interested in the overall chemistry of the reaction, whereas a molecular biologist is more interested in the biology.