Anatomy and Transport Across Plasma Membrane

Running head: BIOSCIENCE
Bioscience
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BIOSCIENCE
Anatomy of plasma membrane
The plasma membrane is defined as the boundary of the cell, which separates the
components of the cell from the extra-cellular components. It is made up of protein and lipid
molecule that forms tough, thin, pliable and hydrophobic barrier around the cell (Luckey et
al., 2014). In other words it can be said that cellular membranes or plasma membrane is
composed of two layers of phospholipid molecule. This bipartite layer has hydrophilic end
and hydrophobic end. The hydrophilic ends are directed towards the inner and the outer
surface of the membrane whereas the hydrophobic ends are buried within the interior of the
membrane (Rodwell et al., 2015).
This arrangement of the plasma membrane is known as fluid mosaic model as
proposed by Singer and Nicolson (Rodwell et al., 2015). According to the fluid mosaic
model, the hydrocarbon chain of phospholipid bilayer forms hydrophobic core that restricts
diffusion of water soluble solutes through the membrane. The polar head group of the
phospholipid has hydrophilic tail that remains embedded within the membrane (Lodish et al.,
2000).
Transport of Oxygen across plasma membrane
Gases such as oxygen (O2) and CO2 (carbon di-oxide) and other small uncharged
molecules which are polar in nature (urea and ethanol) are transported through the plasma
membrane via passive diffusion. These molecules can diffuse across the plasma membrane
without the requirement of transport proteins. Moreover, metabolic energy is not expended
due to the movement of these polar molecules occur from a domain of high concentration to a
region of low concentration, down the chemical concentration gradient. From the theory of
thermodynamics it can be stated that such transportation reactions are spontaneous because it