Direct source of energy for cell processes is ATP (adenosine triphosphate). ATP is produced primarily by cellular respiration, which includes glycolysis in the cytoplasm, the citric acid cycle (Krebs cycle) in the mitochondria, and oxidative phosphorylation (electron transport chain) across the inner mitochondrial membrane. The energy released from ATP hydrolysis (ATP → ADP + Pi) powers most cellular activities, including motor movement, active transport, biosynthesis, and signal transduction. Key points
- ATP as universal energy currency: ATP hydrolysis provides energy for countless cellular processes. The terminal phosphate bond cleavage releases usable energy that drives endergonic reactions and work within the cell.
- Primary production pathways:
- Glycolysis: breaks down glucose in the cytoplasm to form a modest amount of ATP and NADH.
* Citric acid cycle: oxidizes acetyl-CoA to CO2, generating NADH and FADH2, which feed the electron transport chain.
* Oxidative phosphorylation: electron transport chain uses the energy from NADH and FADH2 to pump protons and create a proton gradient that powers ATP synthase, yielding most cellular ATP. Oxygen is the final electron acceptor.
- Sunlight and photosynthesis: in photosynthetic organisms, light energy is converted into chemical energy (ATP and NADPH) which then fuels carbon fixation and other biosynthetic processes. This makes sunlight the ultimate energy source for many cells and ecosystems.
If you’d like, I can tailor this into a concise explainer for a specific audience (e.g., high school students, undergraduates, or a layperson) or expand on how ATP synthase works and how energy coupling drives metabolism.
