Respiration: An Overview
- Glucose is the main respiratory substrate used by cells
- Aerobic respiration is the process of breaking down a respiratory substrate in order to produce ATP using oxygen
- The equation for aerobic respiration:
glucose + oxygen → carbon dioxide + water + energy
C6H1206 + 6 O2 → 6 CO2 + 6 H20 + 2870kJ
- The energy that is released during the process is used to phosphorylate (add a phosphate) ADP to form ATP
- The ATP provides energy for other biological processes in cells
- The process of aerobic respiration using glucose can be split into four stages:
- Glycolysis
- The Link reaction
- The Krebs cycle
- Oxidative phosphorylation
- Glycolysis occurs in the cytoplasm of the cell, while the other three stages all occur within different parts of the mitochondria
- The reactions in each stage of respiration are controlled by enzymes found inside the cell
- The enzyme that catalyses these reactions the slowest will determine the overall rate of aerobic respiration
- Several coenzymes are required during respiration to transfer various molecules involved in the process
- NAD and FAD are the coenzymes responsible for transferring hydrogen between molecules
- Depending on whether they give or take hydrogen, they are able to reduce or oxidise a molecule
- Coenzyme A is responsible for the transfer of acetate (also known as acetic acid) from one molecule to another
- Although glucose is the main fuel for respiration, organisms can also break down other molecules (such as fatty acids or amino acids) to be respired
Structure of mitochondria
- Mitochondria have two phospholipid membranes
- The outer membrane is:
- Smooth
- Permeable to several small molecules
- The inner membrane is:
- Folded (cristae)
- Less permeable
- The site of the electron transport chain (used in oxidative phosphorylation)
- Location of ATP synthase enzymes (used in oxidative phosphorylation)
- The intermembrane space:
- Has a low pH due to the high concentration of protons
- The concentration gradient across the inner membrane is formed during oxidative phosphorylation and is essential for ATP synthesis
- The matrix:
- Is an aqueous solution within the inner membranes of the mitochondrion
- Contains ribosomes, enzymes and circular mitochondrial DNA necessary for mitochondria to function
The structure of a mitochondrion