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Inner membrane
From Wikipedia, the free encyclopedia
The inner membrane is a membrane (phospholipid bilayer) of an organelle that is within the outer membrane. The inner membrane is present within the nuclear envelope, mitochondria and the plastids of eukaryotic cells. The lumen between the inner and outer membranes is referred to as intermembrane space.
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The inner membrane of the nuclear envelope is connected to the outer nuclear envelope membrane through nuclear pores. It contains a number of proteins involved in the structural organization of the nucleus and the attachment of chromatin to the nuclear envelope. In metazoan cells, the inner nuclear membrane contains proteins of the nuclear lamina, a protein meshwork underlying the nuclear envelope and providing structural support. Mutations in inner nuclear envelope proteins can cause nuclear envelopathies, a number of genetic disorders in humans.
The mitochondrial inner membrane forms internal compartments known as cristae, which allow greater space for the proteins such as cytochromes to function properly and efficiently. The electron transport chain is located on the inner membrane of the mitochondria. Within the inner mitochondrial membrane are also transport proteins that transport in a highly controlled manner metabolites across this membrane.
The inner membrane of mitochondria is similar in lipid composition to the membrane of prokaryotes. This phenomenon can be explained by the endosymbiont hypothesis of the origin of mitochondria as prokaryotes internalized by a eukaryotic host cell.
The plastidial inner membrane surrounds the stroma of the plastid. In chloroplasts, extensions of the inner membrane form the thylakoid membrane where the photosystems for photosynthesis are located. The inner and thylakoid membranes are very similar to the membranes found in cyanobacteria. Similar to mitochondria, plastids are thought to have evolved from bacterial endosymbionts.