Calculate RQ values of different respiratory substrates from equations for respiration

SouravOctober 31, 2024

Answer

Let’s calculate the Respiratory Quotient (RQ) values for different respiratory substrates by analyzing the equations for their complete oxidation during cellular respiration. The RQ is calculated as:

RQ = CO2 Produced (moles) / O2 Consumed (moles)

1. Carbohydrates (Glucose)

Equation:
C6H12O6 (Glucose) + 6O2 → 6CO2 + 6H2O

RQ Calculation:

• CO2 Produced: 6 moles
• O2 Consumed: 6 moles
• RQ = 6 CO2 / 6 O2 = 1.00

2. Fats (Palmitic Acid, a typical fatty acid)

Equation:
C16H32O2 (Palmitic Acid) + 23O2 → 16CO2 + 16H2O

RQ Calculation:

• CO2 Produced: 16 moles
• O2 Consumed: 23 moles
• RQ = 16 CO2 / 23 O2 ≈ 0.70

3. Proteins (Generalized Equation for Amino Acids)

Note: The equation varies depending on the amino acid. We’ll use a generalized form, which might not perfectly represent every amino acid’s RQ.

Equation (Simplified for an average amino acid):
C3H7NO2 (Simplified Amino Acid) + 3.5O2 → 2.5CO2 + 2.5H2O + NH3 (later converted to Urea, not affecting RQ)

RQ Calculation (Approximate):

• CO2 Produced: 2.5 moles
• O2 Consumed: 3.5 moles
• RQ ≈ 2.5 CO2 / 3.5 O2 ≈ 0.71

However, the often-quoted average RQ for proteins is around 0.80 due to variations in amino acid structures and the fact that some proteins have more or fewer carbon, hydrogen, oxygen, and nitrogen atoms, affecting the overall RQ.

Summary of RQ Values for Different Substrates:

• Carbohydrates (e.g., Glucose): RQ ≈ 1.00
• Fats (e.g., Palmitic Acid): RQ ≈ 0.70
• Proteins (Average, varies by amino acid): RQ ≈ 0.80 (used commonly, though calculated example gave ≈ 0.71)