Cytoplasmic membrane

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The cytoplasmic membrane is otherwise known as the plasma membrane. The primary function of both eukaryotic and prokaryotic cell membranes is to separate the internal environment of the cell from the outside environment. This is vital for regulating the internal cell environment. The presence of proteins within this membrane facilitates the transport of water-soluble, polar molecules between the external and internal cell environment.

The original cell membrane model, the Fluid Mosaic Model, was proposed by Singer and Nicolson in 1972[1]. Although this model has since been updated as imaging technology has improved it is still widely taught today[2]. The model proposed that cell membranes consisted of a lipid bilayer, with each layer being composed of amphipatic phospholipids. The hydrophilic phosphate heads face the external environment and the hydrophobic tails face inwards[3]. Because of this, only small, non-polar lipid soluble molecules can pass through the bilayer into the cell. To allow addition molecules to enter the cell, the bilayer is embedded with intrinsic and extrinsic proteins. This facilitates the movement of water soluble, charged particles into the cell.


  1. Grisham C and; Garret R. Biochemistry. 6th edition, Canada: Cengage learning. 2016
  2. NCBI - The basic structure and dynamics of cell membranes: an update of the Singer-Nicolson model. 2014 – [cited 12/11/18] Available from -
  3. Banfalvi G. Biological Membranes. 1st Edition, Switzerland: Springer. 2016
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