ATP: How Cells Store and Spend Energy

0:00How do cells store energy, and how do they spend it?

0:05Cells keep energy ready to use in a molecule called ATP, which stands for adenosine triphosphate.

0:13It is adenosine joined to three phosphate groups; tri means three.

0:18Think of ATP as a charged battery, holding energy the cell can use right away.

0:25To spend it, the cell splits off the end phosphate, leaving ADP and a free phosphate.

0:32ADP is adenosine diphosphate, because di means two.

0:37Splitting off that phosphate releases energy, which the cell can use for work.

0:43It powers work such as muscle contraction for movement, active transport, and building molecules like proteins.

0:51Active transport pumps substances across a membrane against their concentration gradient.

0:57Now ADP is like a run-down battery that needs recharging.

1:02Respiration recharges it: these reactions release energy from glucose, mostly inside the cell's mitochondria.

1:10Aerobic respiration uses oxygen: one glucose and six oxygen molecules make six carbon dioxide and six water molecules.

1:20The energy released joins a phosphate back onto ADP, which makes ATP again.

1:27In aerobic respiration, each glucose gives about 30 to 32 ATP, though older textbooks say 36 to 38.

1:37So energy passes from glucose, then to ATP, and then to the work the cell does.

1:44ATP releases energy as it becomes ADP, and respiration turns ADP back into ATP.