What are the major types of cellular molecular energy carriers?

The major types of cellular molecular energy carriers are ATP, FADH2, NADH and NADPH. ATP is the most abundant energy carrier molecule in cells. It is composed of a nitrogen base (adenine), a ribose sugar, and 3 phosphate groups. ATP is made through cellular respiration that occurs in the mitochondria of a cell. More specifically, ATP is made in eukaryotes through oxidative phosphorylation and substrate-level phosphorylation. NADH stands for nicotinamide adenine dinucleotide. It occurs naturally in the body and also plays a key role in generating energy. High energy electrons from NADH are passed along the ETC within the mitochondrial inner membrane. Energy released by their transfer is utilized to fuel the process that generates ATP and consumes molecular oxygen. NADPH is the reduced form of NADP+ and is used in anabolic reactions such as nucleic acid and lipid synthesis, which requires NADPH as a reducing agent. FADH2 stands for flavin adenine dinucleotide. It is a redox enzyme associated with various proteins and a high-energy electronic carrier. It transfers electrons generated in glycolysis and TCA cycle to the ETC.