Mitochondria: Function, Definition, Structure, & Facts

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o Mitochondria are the powerhouses of the eukaryotic cell. According to the endosymbiont theory, mitochondria may have evolved from a symbiotic relationship between ancient prokaryotes and eukaryotes.

o Like prokaryotes, mitochondria have their own circular DNA that replicates independently from the eukaryotic cell.

o This DNA contains no histones or nucleosomes.

o Sections of DNA that aren’t in use are wrapped tightly around globular proteins called histones.

o Eight histones wrapped in DNA form a nucleosome.

o Nucleosomes, in turn, wrap into coils called solenoids, which wrap into supercoils.

o Mitochondrial DNA is passed maternally (from the mother) even in organisms whose male gamete contributes to the cytoplasm.

o The genes in the mitochondrial DNA code for mitochondrial RNA that is distinct from the RNA in the rest of the cell.

o Thus mitochondria have their own ribosomes with a sedimentation factor of 55-60 S.

o Antibiotics that block translation in prokaryotes also seem to work in the mitochondria.

o Mitochondria also have some different codons (presenting an exception to the universal genetic code).

o However, most proteins used by mitochondria are coded for by nuclear DNA, not mitochondrial DNA.

Mitochondria Structure

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o Mitochondria are surrounded by two phospholipid bilayers.

o The inner membrane invaginates to from the cristae.

o It is the inner membrane that holds the electron transport chain.

o Between the inner and outer membrane is the intermembrane space (lower pH and higher [H+] than the matrix).

o Organelles with two membranes: nucleus, mitochondria, and chloroplast.

Mitochondria Function

o TCA / Krebs Cycle: (aerobic, occurs in the cytoplasm for prokaryotes, mitochondrial matrix for eukaryotes).



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