Mitochondria Notes

The transcript states the mitochondria are the powerhouse of the cell; this summarizes their central role in ATP production via cellular respiration.

Mitochondria are double-m membrane-bound organelles (outer membrane and inner membrane).
Inner membrane folds into cristae to greatly increase surface area for housing the electron transport chain and ATP synthase.
Matrix is the interior space containing enzymes of the citric acid cycle, as well as mitochondrial DNA (mtDNA) and mitochondrial ribosomes.
Intermembrane space lies between the outer and inner membranes.
Mitochondria contain their own circular DNA and ribosomes, enabling some autonomous protein synthesis; they replicate and undergo fission/fusion alongside the cell.
Inheritance: mtDNA is typically inherited maternally in humans.

Primary role: production of ATP via oxidative phosphorylation (OXPHOS).
Key stages associated with the mitochondria:
- Pyruvate oxidation (link step) in the mitochondrial matrix: pyruvate → acetyl-CoA + CO₂ + NADH.
- Citric acid cycle (Krebs cycle) in the matrix: acetyl-CoA is oxidized to CO₂, generating NADH, FADH₂, and GTP/ATP.
- Electron transport chain (ETC) and chemiosmosis on the inner mitochondrial membrane: NADH and FADH₂ donate electrons to ETC complexes; proton pumping creates a proton-motive force across the membrane.
ATP synthesis:
- Protons flow back into the matrix through ATP synthase, driving the phosphorylation of ADP to ATP.
- Overall glucose oxidation yields approximately: \mathrm{C6H{12}O6} + 6\ \mathrm{O2} \rightarrow 6\ \mathrm{CO2} + 6\ \mathrm{H2O} + \text{~30-32 ATP}
Energy yield and efficiency:
- Typical yield in eukaryotic cells: ~30–32 ATP per glucose.
- Theoretical maximum in prokaryotes can be ~38 ATP per glucose under ideal conditions; actual yields depend on shuttle systems and other factors.
Byproducts and regulation:
- Water is formed at complex IV; proton leak can generate heat.
- Reactive oxygen species (ROS) are potential byproducts of the ETC; cells have antioxidant systems to mitigate damage.

Glycolysis (in cytosol): glucose → 2 pyruvate + net 2 ATP + 2 NADH.
Pyruvate oxidation: pyruvate → acetyl-CoA + CO₂ + NADH in the mitochondrial matrix.
Citric acid cycle: acetyl-CoA → CO₂ + NADH, FADH₂, and GTP/ATP per turn.
Electron transport chain + chemiosmosis: NADH/FADH₂ powering proton pumping; ATP synthase converts the proton motive force into ATP.

mtDNA is circular and encodes a subset of respiratory chain proteins; additional mitochondrial proteins are encoded by nuclear DNA.
Mitochondrial ribosomes synthesize some mitochondrial-encoded proteins.
Mitochondria replicate and partition during cell division; mtDNA is typically inherited maternally.
Biogenesis relies on coordinated signaling and gene expression; pathways like PGC-1α regulate mitochondrial biogenesis in response to energy demand.

Mitochondrial diseases arise from mutations in mtDNA or nuclear genes affecting mitochondrial function; common symptoms include muscle weakness, neurodegeneration, and lactic acidosis.
Aging and metabolic health are linked to mitochondrial function and ROS management.
Exercise stimulates mitochondrial biogenesis and increases mitochondrial density and efficiency; metabolic adaptations improve with training.

Mitochondrion as a power plant: converts chemical energy from nutrients into ATP, the cell’s usable energy currency.
Cristae as high-efficiency turbine surfaces; inner membrane as the energy-conduction platform; matrix as the energy processing and storage area.

Overall glucose oxidation: \mathrm{C6H{12}O6} + 6\ \mathrm{O2} \rightarrow 6\ \mathrm{CO2} + 6\ \mathrm{H2O} + \text{~30-32 ATP}
ATP synthase reaction: \mathrm{ADP} + \mathrm{P_i} \rightarrow \mathrm{ATP}
Theoretical maximum ATP per glucose (book value):
- In eukaryotes: ~30–32 ATP per glucose.
- In prokaryotes (theoretical maximum): up to ~38 ATP per glucose.