Respiratory substrates & quotients (RQ)

What are respiratory substrates?

Any organic structures that can be used in respiration to produce ATP

Which substrates produce more ATP when respired?

Substrates with more H atoms per unit mass

Carbohydrates

15.8 kJ g⁻¹

Lipids

39.4 kJ g⁻¹

Proteins

17.0 kJ g⁻¹

Respiratory substrates in Aerobic Respiration

Carbohydrates = Glycogen/starch forms glucose

Lipids = Fatty acids break down into 2x Acetyl CoA, then enter the Krebs cycle

Proteins = Proteins break down into amino acids, which are deaminated into pyruvate or Acetyl CoA

What is the Respiratory Quotient?

The ratio of the volumes of oxygen consumed and carbon dioxide given of in respiration

RQ equation

Q1) C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Volumes aren't given here but we do have number of molecules

6CO₂ released / 6O₂ consumed

6/6

1

What's the RQ of carbohydrates?

1

What's the RQ of proteins?

0.9

What's the RQ of lipids?

0.7

Why is the RQ different to the volume of energy produced?

Lipids and proteins RQ value is lower as more oxygen is needed to oxidise them, in comparison to carbohydrates.