Aerobic Respiration

Aerobic Respiration makes the most ATP by completely breaking down glucose into carbon dioxide.

Occurs in 3 stages
Most energy comes electrons taken from glucose to the electron transport chain in the mitochondrion.
NAD+/NADH is a molecule that carries electrons
- NAD+ is the empty version of the molecule (no extra electron)
- NADH is the full version of the molecule (carries extra electron)
FADH2 is another electron carrier

Glycolysis

Glycolysis mean "Sugar-Splitting." This first phase of respiration breaks a 6-carbon molecule of glucose into 2x 3-carbon molecules of Pyruvate.

2 ATP are used to get started
2 NADH molecules are made
4 ATP molecules are made (Net Gain = 2)
2 Pyruvate molecules are made
- can be sent to mitochondria to be broken down further
- can be used to recycle NAD+ if no oxygen is available (fermentation)

Krebs Cycle

Also called the citric acid cycle, Pyruvate is converted to Acetyl CoA, then broken down into individual molecules of Carbon Dioxide.

Per molecule of glucose (2 pyruvate) it makes...
- 8 NADH
- 2 FADH2
- 2 ATP

Electron Transport Chain

The Electron Transport Chain uses the electrons from glucose, brought by NADH and FADH2, to pump hydrogen inside the inner membrane of the mitochondria.

This creates a high concentration that flows back out powering ATP Synthase to make ATP.
- Each NADH powers 3 hydrogen pumps
- Each FADH2 powers 2 hydrogen pumps
- Each hydrogen ion pumped across the membrane can make one ATP as it passes through ATP Synthase
Electrons power the Hydrogen Pumps
Oxygen is used to remove the used electrons
- Without oxygen, the ETC can't pump new H+, NADH can't be recycled, and nothing after glycolysis can function.
- This is the only reason we have to breathe
One oxygen atom combines with electrons and hydrogen ions to make water.

Accounting

The first two stages of aerobic respiration each make some ATP and release electrons for the Electron Transport Chain.

Glycolysis
- 2 ATP
- 2 NADH (x3 = 6 ATP)
Krebs Cycle
- 2 ATP
- 8 NADH (x3 = 24 ATP)
- 2 FADH2 (x2 = 4 ATP)
Total = 38 ATP per molecule of glucose
- some ATP is required to bring the NADH into the mitochondria, so total is often expressed as 36-38 ATP)