ulkikalvojen

Ulkikalvojen, often translated as outer membranes, refers to the outermost layer of a cell or organelle. In bacteria, the outer membrane is a significant component of the cell envelope, found in Gram-negative bacteria. This membrane is a lipid bilayer that contains phospholipids and lipopolysaccharides (LPS), the latter being a unique component that contributes to the structural integrity and pathogenicity of these bacteria. The outer membrane acts as a selective barrier, controlling the passage of molecules into and out of the cell. It also contains porins, which are channel proteins that allow small hydrophilic molecules to diffuse across the membrane.

In eukaryotic cells, the term "outer membrane" typically refers to the outer membrane of organelles like the mitochondria and the nucleus. The mitochondrial outer membrane is a permeable barrier that encloses the organelle and contains porins that allow molecules up to about 5000 Daltons to pass through. The nuclear outer membrane is continuous with the endoplasmic reticulum and is studded with nuclear pores, which regulate the transport of molecules between the nucleus and the cytoplasm. The presence and specific composition of outer membranes are crucial for the function and compartmentalization within cells, playing vital roles in protection, transport, and cellular organization.