Question

At which points in the respiratory pathway different substrates would enter if they were to be respired and used to derive energy.

Answer 1

Part 1: Introduction

• Not all respiratory substrates can enter the respiratory pathways directly, they need to be converted into some intermediates.
• Glucose is the most common substrate for respiration but sucrose can also be utilized in glycolysis for respiration by breaking it down into glucose.
• Fats are broken down to fatty acids and glycerol, whereas proteins are broken down to amino acids.These fatty acids and amino acids further enter the krebs cycle in the form acetyl CoA.
• Glycerol is converted to phosphoglyceraldehyde which further enters the glycolysis pathway.

Part 2: Entry points of different respiratory substrates in respiration
$\begin{array}{ccc}\text{Respiratory Substrates}& \text{Converted into a substrate}& \\ & \text{to enter in respiration}& \text{Respiratory pathway in which they enter}\\ \text{Carbohydrates like sucrose, fructose, etc}& \text{Glucose}& \text{Glycolysis}\\ \text{Fatty acids (from fats)}& \text{Acetyl CoA}& \text{Kerbs cycle}\\ \text{Glycerol (from fats)}& \text{Phosphoglyceraldehyde}& \text{Glycolysis}\\ \text{Amino acids (from proteins)}& \text{Acetyl CoA, pyruvic acid}& \text{Krebs cycle}\end{array}$