<p>Molecular biology focuses on DNA, RNA, transciption and regulation of it, and protein production in the cell.</p>
<p>Biochemistry is more focused on proteins and enzymes and the functions of them. It also focuses a lot on metabolism. </p>
<p>Cell biology focuses on whole cells, cell types and IDing them, cell cycle, the the condition of cells, Cell compartments (golgi, ER, mitocondria), culturing cells.</p>
<p>As you might imagine there is large overlap between the disciplines but in general nucleic acids = mol bio, biochemistry = proteins and cell bio = cells.</p>