Mitochondria
Mitochondria are double-membrane-bound organelles found in the cytoplasm of eukaryotic cells that serve as the primary site of cellular respiration, generating adenosine triphosphate (ATP) through oxidative phosphorylation on the inner membrane's folds called cristae. They contain their own circular DNA and ribosomes, supporting the endosymbiotic theory that they evolved from ancient free-living bacteria engulfed by ancestral eukaryotic cells. Mitochondria regulate cell metabolism, calcium signaling, and apoptosis, and their number in a cell varies from one to several thousand depending on the cell's energy demands.
Mitochondrial Structure and Associated Functions
| Structure | Description | Function |
|---|---|---|
| Outer membrane | Smooth double phospholipid membrane | Regulates passage of molecules; contains porins |
| Inner membrane | Highly folded membrane | Site of electron transport chain and ATP synthase |
| Cristae | Folds of inner membrane | Increase surface area for ATP production |
| Matrix | Fluid inside inner membrane | Site of Krebs cycle (citric acid cycle); contains mitochondrial DNA |
| Intermembrane space | Space between outer and inner membranes | Proton reservoir for chemiosmosis |
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Related Terms
Eukaryote
A eukaryote is an organism whose cells contain a membrane-bound nucleus housing the DNA, along with other membrane-enclosed organelles such as mitochondria, endoplasmic reticulum, and the Golgi apparatus. Eukaryotes include all plants, animals, fungi, and protists, and their cells are generally much larger and more structurally complex than prokaryotic cells. The compartmentalization of cellular functions within organelles allows eukaryotes to perform more specialized and regulated biochemical processes.
Chloroplast
Chloroplasts are double-membrane-bound organelles found exclusively in plant cells and algae that capture light energy and convert it into chemical energy through photosynthesis, producing glucose and oxygen from carbon dioxide and water. They contain a system of flattened membrane sacs called thylakoids, arranged in stacks called grana, which house the light-absorbing pigment chlorophyll and the protein complexes of the light-dependent reactions. Like mitochondria, chloroplasts contain their own circular DNA and ribosomes, supporting the endosymbiotic theory that they evolved from ancient photosynthetic cyanobacteria.
Cell Nucleus
The cell nucleus is a large, membrane-bound organelle found in eukaryotic cells that serves as the control center of the cell, housing the cell's genetic material (DNA) organized into chromosomes. It is surrounded by a double membrane called the nuclear envelope, which contains nuclear pores that regulate the transport of molecules between the nucleus and the cytoplasm. The nucleus directs cell activities by controlling gene expression, coordinating DNA replication during cell division, and producing ribosomal RNA in a specialized subregion called the nucleolus.
From Greek "mitos" meaning thread and "chondrion" meaning small granule. The term was coined by German microbiologist Carl Benda in 1898 to describe the thread-like structures he observed in cells under the light microscope.