 ATP is consumed in the cell by energy @-@ requiring ( endergonic ) processes and can be generated by energy @-@ releasing ( exergonic ) processes . In this way ATP transfers energy between spatially separate metabolic reactions . ATP is the main energy source for the majority of cellular functions . This includes the synthesis of macromolecules , including DNA and RNA ( see below ) , and proteins . ATP also plays a critical role in the transport of macromolecules across cell membranes , e.g. exocytosis and endocytosis . 
