Atp

High-energy currency

Figure 2.12 Regenerating ATP. ATP is regenerated from ADP and phosphate during the process of cellular respiration.

Glucose

1. After food is digested, nutrients are absorbed from small intestine to bloodstream.

1. After food is digested, nutrients are absorbed from small intestine to bloodstream.

Fatty acids Glycerol —

Glucose

Amino acids

2. Nutrients are transported in bloodstream to cells.

2 ADP+P

2 ADP+P

Fatty acids Glycerol —

Amino acids

3. Nutrients enter cells in various forms.

4. Final step in the breakdown of food to produce energy occurs by cellular respiration.

3. Nutrients enter cells in various forms.

4. Final step in the breakdown of food to produce energy occurs by cellular respiration.

5. The released energy is stored in the form of ATP.

Figure 2.13 Cellular respiration. Carbohydrates, proteins, and fats are broken down inside a mitochondrion. The energy released by their digestion is used to synthesize ATP.

Cellular respiration occurs in the mitochondria of both plant and animal cells and results in the production of ATP. ATP energizes other compounds through phosphorylation, which means it adds a phosphate to them. (You can think of the donated phosphate as a "little bag of energy.") When a molecule, say an enzyme, needs energy, the phosphate group is transferred from ATP to the enzyme, and the enzyme now has the energy it needs to perform its job. When ATP gives away a phosphate group, it becomes adenosine diphosphate or ADP. ATP is then regenerated from ADP and phosphate by the process of cellular respiration (Figure 2.12).

All of the foods you eat undergo cellular respiration. In this process, cells utilize oxygen and produce carbon dioxide and water (this is why you breathe oxygen in and breathe carbon dioxide out), and the energy stored in the chemical bonds of the nutrients is used to produce ATP (Figure 2.13). The ATP that is produced can then be used to power cellular activities, such as helping an enzyme perform its job (Figure 2.14).

Media Activity 2.1D ATP Production in the Cell

Enzyme Phosphorylated

(energized) enzyme

Enzyme Phosphorylated

(energized) enzyme

Figure 2.14 Phosphorylation. The terminal phosphate group of an ATP molecule can be transferred to another molecule, in this case a protein, to energize it. When ATP loses a phosphate it becomes ADP. The protein that gained the phosphate group becomes energized.

Essay 2.1

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