5.7.8(Respiratory substrates)

What is the respiratory quotient equation

• RQ = CO₂ produced/ O₂ consumed

What is the RQ values for glucose, fatty acids and amino acids

• Glucose: 1

• Fatty acids: 0.7

• Amino acids: 0.8

What do different RQ values indicate

• If the RQ value is 1 or below, then aerobic respiration is taking place

• If the RQ value is greater than 1 then anaerobic respiration is taking place

Describe how carbohydrates can be used as respiratory substrates

1. Disaccharides can be digested to monosaccharides for respiration

2. Monosaccharides such as fructose and galactose can be changed, by isomerase enzymes, to glucose for respiration

Describe how fatty acids can be used as respiratory substrate

1. Glycerol:

   • Triglycerides are hydrolysed by lipase to glycerol and fatty acids

   • Glycerol can then be converted into triose phosphate and to pyruvate and fed into the link reaction

2. Fatty acids:

   • Fatty acids can be combined with CoA to form a fatty acid- CoA complex

   • In the matrix, it is then broken down into acetyl CoA which can be fed into the krebs cycle

Describe how proteins can be used as respiratory substrates

• Deaminated amino acids leave keto acids

• These enter the respiratory pathway as:

  • Pyruvate or acetate

  • Converted into Acetyl-coA and enter link reaction

  • Can enter krebs cycle directly

Describe when keto acids are used as respiratory substrates

• They are used when there is insufficient glucose or lipids due to fasting starvation or prolonged exercise