4.1 Chemical Energy and ATP

Key Concept

• All cells need chemical energy.

Main Ideas

• The chemical energy used for most cell processes is carried by ATP (adenosine triphosphate).
• Organisms break down carbon-based molecules to produce ATP.
• Some organisms do not need sunlight and photosynthesis for energy.

Vocabulary

• ATP: Adenosine triphosphate, a molecule that transfers energy from the breakdown of food molecules to cell processes.
• ADP: Adenosine diphosphate, a lower-energy molecule that can be converted into ATP by the addition of a phosphate group.
• Chemosynthesis: Process by which some organisms use chemical energy instead of light energy to make energy-storing carbon-based molecules.

ATP and ADP

• ATP transfers energy to cell processes.
• ADP is converted into ATP by adding a phosphate group.
• ATP has three phosphates; removing one releases energy, converting ATP to ADP.
• The breakdown of ATP to ADP and the production of ATP from ADP involves complex proteins.

Energy in Food

• Foods contain carbon-based molecules storing chemical energy in bonds.
  • Carbohydrates and lipids are primary energy sources.
  • Energy is released after food molecules are broken down.
• The breakdown of glucose (a carbohydrate) yields about 36 ATP molecules.
• Lipids store the most energy, yielding more ATP than carbohydrates.
  • A triglyceride can be broken down to make about 146 ATP molecules.
  • Lipids hold about 80% of the body's energy.
• Proteins store similar energy amounts as carbohydrates, but are used less for ATP production.

Photosynthesis and Chemosynthesis

• Plants: Use sunlight to make sugars for ATP production.
• Chemosynthesis: Used by organisms in environments without sunlight (e.g., hydrothermal vents).
  • Chemosynthetic organisms use chemical compounds as energy sources.

Comparing Energy Sources

• Plants vs. Chemosynthetic organisms:
  • Both make food, but with different raw materials.

Reviewing Main Ideas

1. ATP and ADP Relationship: ATP becomes ADP when a phosphate group is removed.
2. Molecules Broken Down for ATP:
   • Typically carbohydrates and lipids; carbohydrates are often used.
3. Organisms Without Sunlight:
   • Utilize chemosynthesis to survive in environments like the deep ocean.

Critical Thinking Questions

1. Energy from Food: Energy is not received directly; it requires food digestion and molecule breakdown.
2. Plants vs. Animals Energy Needs:
   • Both need ATP but obtain it differently; plants make sugars via photosynthesis.
3. Chemical Reaction of ATP Breakdown:
   • Adding Water: ATP + H₂O → ADP + Phosphate Group.