The mitochondrion is a double-membrane-bound organelle that plays a critical role in energy production and various cellular processes. Its structure consists of the following key components:

1. Outer Membrane: This smooth membrane encloses the mitochondrion and contains porins, protein channels that allow the passage of ions, nutrients, and small molecules. It serves as a barrier and regulates the exchange of materials between the mitochondrion and the cytoplasm.

2. Intermembrane Space: The narrow space between the outer and inner membranes. It is involved in several metabolic reactions and serves as a reservoir for protons during oxidative phosphorylation.

3. Inner Membrane: This highly folded membrane forms structures called cristae, which significantly increase its surface area. The inner membrane contains proteins and enzymes essential for the electron transport chain and ATP synthesis. It is impermeable to most molecules, ensuring the maintenance of a proton gradient.

4. Cristae: The infoldings of the inner membrane that create more surface area for oxidative phosphorylation and ATP production. They house the protein complexes of the electron transport chain and ATP synthase.

5. Matrix: The innermost compartment of the mitochondrion, enclosed by the inner membrane. It contains mitochondrial DNA, ribosomes, and enzymes involved in the citric acid cycle (Krebs cycle), fatty acid oxidation, and other metabolic pathways. The matrix is also the site of mitochondrial protein synthesis.

6. Mitochondrial DNA (mtDNA): A small, circular DNA molecule found within the matrix. It encodes some of the proteins and RNA necessary for mitochondrial function, although most mitochondrial proteins are encoded by nuclear DNA and imported into the organelle.

The unique double-membrane structure of the mitochondrion and its specialized components enable it to perform its primary function: the production of ATP through oxidative phosphorylation. Additionally, mitochondria are involved in processes such as apoptosis (programmed cell death), calcium storage, and the regulation of cellular metabolism.