Simplify the following text for a Grade 17 native English-speaking person.
Original: Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell , including the interrelationship of DNA , RNA and protein biosynthesis and learning how these interactions are regulated .
Simplified: Molecular biology chiefly concerns itself with understanding and the interactions between the various systems of a cell , including the interactions between the different types of DNA , RNA and protein biosynthesis as well as learning how these interactions are regulated .