Cells are the basic components of living organisms. The two major types of cells are prokaryotic and eukaryotic cells. Eukaryotic cells have membrane-bound organelles that perform essential cell functions. Mitochondria are considered the “powerhouses” of eukaryotic cells. What does it mean to say that mitochondria are the cell’s power producers? These organelles generate power by converting energy into forms that are usable by the cell. Located in the cytoplasm, mitochondria are the sites of cellular respiration. Cellular respiration is a process that ultimately generates fuel for the cell’s activities from the foods we eat. Mitochondria produce the energy required to perform processes such as cell division, growth, and cell death.
Mitochondria have a distinctive oblong or oval shape and are bounded by a double membrane. The inner membrane is folded creating structures known as cristae. Mitochondria are found in both animal and plant cells. They are found in all body cell types, except for mature red blood cells. The number of mitochondria within a cell varies depending on the type and function of the cell. As mentioned, red blood cells do not contain mitochondria at all. The absence of mitochondria and other organelles in red blood cells leaves room for the millions of hemoglobin molecules needed in order to transport oxygen throughout the body. Muscle cells, on the other hand, may contain thousands of mitochondria needed to provide the energy required for muscle activity. Mitochondria are also abundant in fat cells and liver cells.
Mitochondria have their own DNA, ribosomes and can make their own proteins. Mitochondrial DNA (mtDNA) encodes for proteins that are involved in electron transport and oxidative phosphorylation, which occur in cellular respiration. In oxidative phosphorylation, energy in the form of ATP is generated within the mitochondrial matrix. Proteins synthesized from mtDNA also encode for the production of the RNA molecules transfer RNA and ribosomal RNA.
Mitochondrial DNA differs from DNA found in the cell nucleus in that it does not possess the DNA repair mechanisms that help prevent mutations in nuclear DNA. As a result, mtDNA has a much higher mutation rate than nuclear DNA. Exposure to reactive oxygen produced during oxidative phosphorylation also damages mtDNA.
Mitochondrion Anatomy and Reproduction
Mitochondria are bounded by a double membrane. Each of these membranes is a phospholipid bilayer with embedded proteins. The outermost membrane is smooth while the inner membrane has many folds. These folds are called cristae. The folds enhance the “productivity” of cellular respiration by increasing the available surface area. Within the inner mitochondrial membrane are a series of protein complexes and electron carrier molecules, which form the electron transport chain (ETC). The ETC represents the third stage of aerobic cellular respiration and the stage where the vast majority of ATP molecules are generated. ATP is the body’s main source of energy and is used by cells to perform important functions, such as muscle contraction and cell division.
The double membranes divide the mitochondrion into two distinct parts: the intermembrane space and the mitochondrial matrix. The intermembrane space is the narrow space between the outer membrane and the inner membrane, while the mitochondrial matrix is the area that is completely enclosed by the innermost membrane. The mitochondrial matrix contains mitochondrial DNA (mtDNA), ribosomes, and enzymes. Several of the steps in cellular respiration, including the Citric Acid Cycle and oxidative phosphorylation occur in the matrix due to its high concentration of enzymes.
Mitochondria are semi-autonomous in that they are only partially dependent on the cell to replicate and grow. They have their own DNA, ribosomes, make their own proteins, and have some control over their reproduction. Similar to bacteria, mitochondria have circular DNA and replicate by a reproductive process called binary fission. Prior to replication, mitochondria merge together in a process called fusion. Fusion is needed in order to maintain stability as, without it, mitochondria will get smaller as they divide. These smaller mitochondria are not able to produce sufficient amounts of energy needed for proper cell function, then we need to give it more energy in the form of Near Infra Red Spinning Magnetic Wave energy (NIRSMW) that is absorbed by mitochondria, which perform the function of producing cellular energy called “ATP”