The Power Plant
The primary source of cellular energy in nonphotosynthetic cells is glucose. The complete aerobic degradation of glucose to CO² and H²O is coupled to the synthesis of as many as 32 molecules of ATP.
In eukaryotic cells, the initial stages of glucose degradation occur in the cytosol, and the terminal stages, including those involving oxygen, occur in the mitochondria. Two ATPs are generated in the cytosol. As many as 30 are generated in the mitochondria: much of the energy released in the mitochondrial oxidation can be used for other purposes, such as heat generation and transportation of molecules into or out of the mitochondrion. Nonetheless, the mitochondrion can still be regarded as the «power plant» of the cell.Individual Mitochondria
In eukaryotic cells, mitochondria are large enough to be seen under the light microscope. As a cell grows, its mitochondria increase in size and one or more daughter mitochondris pinch off in a manner similar to the way in which bacterial cells grow and divide. Mitochondrial growth and division is not coupled to nuclear division of the cell.Mitochondria contain their on genetic system and exhibit cytoplasmic inheritance. Mitochondrial DNA (mtDNA) is located in the matrix of the mitochondrion and is sometimes found attatched to the inner mitochondrial membrane. In human mtDNA a completely sequenced circular molecule of 16,569 bp, is among the smallest known. Studies now suggest that genes moved from the mitochondria to the cell nucleus, or vise versa, during evolution. Translocations of short segments of mtDNA to nuclear DNA may be occuring still.
The genetic code used in mitochondria is different from the standard code used in all prokaryotic and eukaryotic nuclear genes; the code is even different in mitochondria from different species.
In humans, the sperm contributes little cytoplasm to the zygote, and consiquently, most (if not all) of the mitochondria in the embryo must be derived from those of the mother (via the egg), not the father (via the sperm).
