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.