Aerobic Respiration: Overview
Occurs in Four Distinct Stages:
1. Glycolysis: 10-step process in the
cytoplasm.
2. Pyruvate Oxidation: 1-step process in the
mitochondrial matrix.
3. Krebs Cycle: 8-step cyclical process in the
mitochondrial matrix.
4. Electron Transport Chain &
Chemiosmosis: Multi-step process in the
inner mitochondrial membrane.
Energy Transfer Terminology
Substrate-level Phosphorylation:
• ATP forms directly in an enzyme-catalyzed
reaction.
Oxidative Phosphorylation:
• ATP forms indirectly through a series of
enzyme-catalyzed redox reactions involving
oxygen as the final electron acceptor.
Energy Carriers
• NAD+ and FAD+ are low energy,
oxidized coenzymes that act as electron
acceptors.
• When an electron(s) are added to these
molecules, they become reduced to
NADH and FADH2.
• In this case, reducing a molecule gives
it more energy.
Cellular Respiration:
The Details
Glycolysis
• 2 ATPs are used in
steps 1 & 3 to prepare
glucose for splitting.
• F 1,6-BP splits into
DHAP and G3P.
• DHAP converts to G3P.
• 2 NADH are formed in
step 6.
• 2 ATP are formed by
substrate-level
phosphorylation in both
steps 7 and 10.
• 2 pyruvates are
produced in step 10.
Glycolysis
Energy Yield & Products:
4 ATP produced – 2 ATP used = 2 net ATP
2 NADH
2 pyruvates
Further processing in aerobic
cellular respiration
(if oxygen is available)
Mitochondria
Highly folded
Smooth
Folds of the inner
membrane
Protein-rich liquid
Fluid-filled
intermembrane
space
See PDF Glycolysis
Pyruvate Oxidation
(if oxygen is present…)
The following occurs for each pyruvate:
1. CO2 removed.
2. NAD+ reduced to NADH and the
2-carbon compound becomes acetic
acid.
3. Coenzyme A (CoA) attaches to
acetic acid to form acetyl-CoA.
Pyruvate Oxidation
Pyruvate Oxidation
Energy Yield & Products:
2 NADH
2 acetyl-CoA
2 CO2 (released as waste)
See PDF Pyruvate Oxidation
The Krebs Cycle
Occurs twice for each molecule of glucose, 1 for each acetyl-CoA.
The Krebs Cycle
1. In step 1, acetyl-CoA combines with
oxaloacetate to form citrate.
2. In step 2, citrate is rearranged to isocitrate.
3. NAD+ is reduced to NADH in steps 3, 4 and 8.
4. FAD is reduced to FADH2 in step 6.
5. ATP if formed in step 5 by substrate-level
phosphorylation. The phosphate group from
succinyl-CoA is transferred to GDP, forming
GTP, which then forms ATP.
6. In step 8, oxaloacetate is formed from malate,
which is used as a reactant in step 1.
7. CO2 is released in steps 3 and 4.
The Krebs Cycle
Energy Yield & Products:
2 ATP
6 NADH
2 FADH2
4 CO2 (released as waste)
NADH and FADH2 carry electrons to the electron
transport chain for further production of ATP by
oxidative phosphorylation.
See PDF Krebs