Overview
This lecture explains the respiratory quotient (RQ), how to calculate it for different respiratory substrates, and what RQ indicates about the substrate being used.
Introduction to Respiratory Quotient (RQ)
- The respiratory quotient (RQ) is the ratio of carbon dioxide produced to oxygen consumed during respiration.
- RQ helps determine which respiratory substrate (carbohydrate, lipid, or protein) is being used for respiration.
Calculating RQ for Different Substrates
-
Carbohydrates (e.g., glucose): Balanced equation for glucose respiration shows 6 CO₂ produced and 6 O₂ consumed.
-
RQ for carbohydrates = 6 ÷ 6 = 1.
-
If RQ = 1, the organism is respiring carbohydrates.
-
Lipids (e.g., fatty acids): Example equation produces 16 CO₂ and requires 23 O₂ molecules.
-
RQ for lipids = 16 ÷ 23 ≈ 0.7.
-
If RQ ≈ 0.7, the organism is respiring lipids.
-
Proteins: RQ is more complex due to varied amino acid formulas, but typically RQ ≈ 0.9.
-
If RQ ≈ 0.9, the organism is respiring proteins.
Interpreting RQ Values
- RQ values help identify which type of substrate (carbohydrate, lipid, or protein) is being respired.
- Different substrates yield different RQ values due to their chemical compositions.
Key Terms & Definitions
- Respiratory Quotient (RQ) — The ratio of the volume of CO₂ produced to the volume of O₂ consumed during respiration.
- Respiratory substrate — A molecule (carbohydrate, lipid, or protein) used for energy production in respiration.
Action Items / Next Steps
- Practice balancing respiration equations for different substrates.
- Memorize typical RQ values for carbohydrates, lipids, and proteins.