Mitochondria and the Electron Transport Chain (ETC):
Comprehensive Notes
I. Introduction to Mitochondria
Mitochondria are dynamic, double-membraned organelles critical
for cellular energy metabolism. Often termed the "powerhouses
of the cell," their principal role is to generate adenosine
triphosphate (ATP) through the process of oxidative
phosphorylation. However, their functions extend far beyond
mere energy production, encompassing roles in cell signaling,
apoptosis, metabolic regulation, and biosynthetic pathways.
II. Key Functions of Mitochondria
1. ATP Production via Oxidative Phosphorylation
The primary energy-yielding process occurs across the inner
mitochondrial membrane (IMM) via the Electron Transport
Chain (ETC) and ATP synthase.
ATP is synthesized as electrons donated by reduced
cofactors (NADH and FADH₂) pass through ETC complexes,
, driving proton pumping and the generation of the proton
motive force (PMF).
2. Mitochondrial Genome and Protein Expression
Mitochondria possess their own circular DNA (~16.5–17 kb)
encoding 13 essential polypeptides, 22 tRNAs, and 2 rRNAs.
These components are crucial for the assembly and function
of ETC complexes.
Despite this autonomy, ~99% of mitochondrial proteins are
encoded by nuclear genes, translated in the cytosol, and
imported post-translationally via specialized translocases.
3. Generation and Regulation of Reactive Oxygen Species (ROS)
As electrons leak from the ETC, particularly at Complexes I
and III, superoxide (O₂⁻) and other ROS are formed.
At physiological levels, ROS act as signaling molecules;
however, excess ROS lead to oxidative damage,
mitochondrial dysfunction, and disease pathogenesis.
Antioxidant systems (e.g., superoxide dismutase, glutathione
peroxidase) mitigate oxidative stress.
4. Calcium Homeostasis
Comprehensive Notes
I. Introduction to Mitochondria
Mitochondria are dynamic, double-membraned organelles critical
for cellular energy metabolism. Often termed the "powerhouses
of the cell," their principal role is to generate adenosine
triphosphate (ATP) through the process of oxidative
phosphorylation. However, their functions extend far beyond
mere energy production, encompassing roles in cell signaling,
apoptosis, metabolic regulation, and biosynthetic pathways.
II. Key Functions of Mitochondria
1. ATP Production via Oxidative Phosphorylation
The primary energy-yielding process occurs across the inner
mitochondrial membrane (IMM) via the Electron Transport
Chain (ETC) and ATP synthase.
ATP is synthesized as electrons donated by reduced
cofactors (NADH and FADH₂) pass through ETC complexes,
, driving proton pumping and the generation of the proton
motive force (PMF).
2. Mitochondrial Genome and Protein Expression
Mitochondria possess their own circular DNA (~16.5–17 kb)
encoding 13 essential polypeptides, 22 tRNAs, and 2 rRNAs.
These components are crucial for the assembly and function
of ETC complexes.
Despite this autonomy, ~99% of mitochondrial proteins are
encoded by nuclear genes, translated in the cytosol, and
imported post-translationally via specialized translocases.
3. Generation and Regulation of Reactive Oxygen Species (ROS)
As electrons leak from the ETC, particularly at Complexes I
and III, superoxide (O₂⁻) and other ROS are formed.
At physiological levels, ROS act as signaling molecules;
however, excess ROS lead to oxidative damage,
mitochondrial dysfunction, and disease pathogenesis.
Antioxidant systems (e.g., superoxide dismutase, glutathione
peroxidase) mitigate oxidative stress.
4. Calcium Homeostasis
