1. Glucose: Animals obtain glucose from the food they consume.
2. Glycolysis: The first stage of cellular respiration breaks down glucose into pyruvate, producing a small amount of ATP (2 molecules).
3. Krebs Cycle (Citric Acid Cycle): Pyruvate is further broken down, producing electron carriers (NADH and FADH2). This cycle also generates a small amount of ATP.
4. Electron Transport Chain: The electron carriers from the Krebs Cycle deliver electrons to the electron transport chain. As electrons move down the chain, energy is released and used to pump protons across the inner mitochondrial membrane, creating a proton gradient.
5. ATP Synthase: The flow of protons back across the membrane through ATP synthase drives the production of large amounts of ATP (approximately 32 molecules per glucose molecule).
In summary: The energy stored in ATP molecules in animal cells originates from the chemical bonds of glucose, which is broken down in a series of reactions that ultimately release energy used to drive ATP synthesis.
It's important to note that while glucose is the primary fuel source, animal cells can also obtain energy from the breakdown of other molecules like fats and proteins.
