Mitochondria
Mitochondria are double-membrane bound organelles that function as the primary site of ATP production in eukaryotic cells. They are essential for aerobic respiration and also play important roles in apoptosis, cell differentiation, growth, and cell cycle regulation.
I. Structure
Mitochondria have a unique structure that reflects their functions:
- Outer Membrane: The outer membrane is relatively permeable due to the presence of porin proteins, which allow small molecules to pass freely.
- Inner Membrane: The inner membrane is highly selective and impermeable to ions. It is folded into numerous cristae, which greatly increase the surface area available for oxidative phosphorylation. Embedded within this membrane are the electron transport chain (ETC) complexes and ATP synthase, both essential for ATP generation.
- Intermembrane Space: The space between the two membranes is narrow and acts as a reservoir for protons pumped across the inner membrane during electron transport.
- Matrix: The innermost compartment, the matrix, is a dense, enzyme-rich fluid. It contains the enzymes of the Krebs cycle and β-oxidation, as well as mitochondrial DNA (mtDNA), ribosomes, tRNAs, and mRNAs. This allows mitochondria to synthesize some of their own proteins.