Cells primarily get their energy from the breakdown of food molecules, a process called cellular respiration.
Fuel Molecules:
Cells use complex organic molecules like sugars, fats, and proteins as fuel sources.
These molecules store energy within their chemical bonds.
Energy Release:
Cellular respiration breaks down these complex molecules into simpler ones, releasing the stored energy.
This process happens in a series of steps, each extracting some energy.
The main energy currency produced in cells is Adenosine Triphosphate (ATP). ATP acts like a rechargeable battery, providing quick energy for various cellular functions.
Key Pathways:
Glycolysis: This initial step breaks down glucose (a sugar molecule) into pyruvate, releasing some ATP and energy-rich molecules like NADH.
Citric Acid Cycle (Krebs Cycle): Pyruvate is further broken down in the mitochondria (the cell's "powerhouse") within this cycle, generating more ATP and NADH.
Electron Transport Chain: NADH and other energy carriers from previous steps transfer their energy to create a proton gradient across the mitochondrial membrane. This gradient is used to pump protons back into the mitochondria, ultimately leading to ATP production through a process called oxidative phosphorylation.
Photosynthesis: In plants and some other organisms, photosynthesis captures energy from sunlight to convert water and carbon dioxide into sugars, providing the initial fuel source for cellular respiration.
Energy Storage: Excess energy not immediately needed can be stored in molecules like glycogen (in animals) or starch (in plants) for later use.