Respiration and ATP production, at a glance

One glucose forms two pyruvate, with net two ATP and two reduced NAD in the cytosol.

• Cytosol: glucose -> two pyruvate.
• Four ATP made minus two invested = net two.
• Two NAD reduced; oxidised NAD must be regenerated.

Keep in mind: It does not directly use oxygen; its continuation depends on regenerating NAD, which fermentation can provide.

The link reaction forms acetyl coenzyme A; the Krebs cycle releases its carbon as CO2 while reducing electron carriers.

• Link reaction per glucose: 2 CO2 and 2 NADH.
• Two Krebs turns per glucose.
• Krebs per glucose: 4 CO2, 6 NADH, 2 reduced FAD and 2 ATP equivalents.

Keep in mind: It is regenerated as the cycle proceeds, allowing repeated acetyl-group entry.

Electron transfer pumps protons out of the matrix; their return through ATP synthase drives ATP formation, with oxygen accepting electrons at the end.

• Protons pumped: matrix -> intermembrane space.
• Protons return through ATP synthase to matrix.
• Oxygen accepts electrons and forms water.

Keep in mind: Inorganic phosphate supplies the phosphate; oxygen accepts electrons and protons to form water.

Fermentation reoxidises reduced NAD so glycolysis can continue; it does not add ATP beyond glycolysis in these pathways.

• Lactate pathway: pyruvate reduced, NAD regenerated.
• Yeast: pyruvate -> ethanal + CO2 -> ethanol.
• Net yield remains two ATP per glucose from glycolysis.

Keep in mind: It regenerates NAD; the standard anaerobic ATP yield comes from glycolysis.

A valid respiration measurement separates biological gas exchange from temperature, pressure and sample-size effects.

• CO2 absorption makes gas decline reflect O2 uptake.
• Use an equilibrated matched control.
• Normalise rates to time and sample amount.

Keep in mind: Cooling, pressure changes and leaks can also affect gas volume; controls are needed.