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Illustration of a eukaryotic cell membrane Comparison of a eukaryotic vs. a prokaryotic cell membrane. The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extracellular space).
Hence, the layer is called a phospholipid bilayer, or sometimes a fluid mosaic membrane. Embedded within this membrane is a macromolecular structure called the porosome the universal secretory portal in cells and a variety of protein molecules that act as channels and pumps that move different molecules into and out of the cell. [2]
There is a simple division of labor in cells—genes give instructions and proteins carry out these instructions, tasks like building a new copy of a cell, or repairing the damage. [6] Each type of protein is a specialist that only does one job, so if a cell needs to do something new, it must make a new protein to do this job.
The outer membrane is also continuous with the inner nuclear membrane since the two layers are fused together at numerous tiny holes called nuclear pores that perforate the nuclear envelope. These pores are about 120 nm in diameter and regulate the passage of molecules between the nucleus and cytoplasm, permitting some to pass through the ...
It is lined with a fiber network called the nuclear lamina which is 10-40 nm thick and provides strength. [citation needed] Mutations in the genes that encode for the inner nuclear membrane proteins can cause several laminopathies. [citation needed]
Schematic representation of transmembrane proteins: 1) a single-pass membrane protein 2) a multipass membrane protein (α-helix) 3) a multipass membrane protein β-sheet. The membrane is represented in light yellow. A transmembrane protein is a type of integral membrane protein that spans the entirety of the cell membrane.
Fluid mosaic model of a cell membrane. The fluid mosaic model explains various characteristics regarding the structure of functional cell membranes.According to this biological model, there is a lipid bilayer (two molecules thick layer consisting primarily of amphipathic phospholipids) in which protein molecules are embedded.
The complementary process that involves increase in quantities of cellular components is called upregulation. [ 1 ] An example of downregulation is the cellular decrease in the expression of a specific receptor in response to its increased activation by a molecule, such as a hormone or neurotransmitter , which reduces the cell's sensitivity to ...