Rucete ✏ Campbell Biology In a Nutshell
Unit 2 THE CELL — Concept 9.1 Catabolic Pathways Yield Energy by Oxidizing Organic Fuels
Cells extract energy by breaking down organic molecules in a series of redox reactions. This energy is then used to power cellular work, especially through the production of ATP—the currency of life.
1. Catabolic Pathways and ATP Production
- Catabolism refers to the breakdown of complex molecules into simpler compounds, releasing energy in the process.
- This energy is captured in the form of ATP (adenosine triphosphate), the molecule cells use to perform work.
2. Fermentation and Cellular Respiration
- Fermentation:
- An anaerobic process (no oxygen required)
- Produces ATP by partially breaking down sugars
- Cellular respiration:
- A more efficient aerobic process (requires oxygen)
- Fully breaks down glucose into CO₂ and H₂O
- Yields much more ATP than fermentation
3. Redox Reactions: Fueling the Flow of Energy
- Oxidation: The loss of electrons from a substance
- Reduction: The gain of electrons by a substance
- In respiration:
- Glucose is oxidized (loses electrons)
- Oxygen is reduced (gains electrons)
- These redox reactions release energy used for ATP synthesis
4. Electron Carriers: NAD⁺ and the Electron Transport Chain
- NAD⁺ (Nicotinamide adenine dinucleotide):
- Functions as an electron shuttle
- Accepts electrons during oxidation and becomes NADH
- Electron Transport Chain (ETC):
- A series of proteins embedded in membranes
- Transfers electrons from NADH and FADH₂ to oxygen in a controlled stepwise fashion
- This gradual energy release drives ATP production
In a Nutshell
- Catabolic pathways break down organic molecules to release energy.
- Redox reactions are the basis for extracting energy from food.
- NAD⁺ and the electron transport chain are central to moving and converting that energy into usable ATP.
- Respiration is efficient, and cells rely on it to power nearly all biological work.