Transport of Substances across the Plasma Membrane in Eukaryotic Cells

These are made of short branching carbohydrate chains attached to proteins and lipids in the membrane. They give other functions to the membrane. For example they allow the proteins to act as receptors that would detect chemical molecules such as hormones and trigger an action within the cell.1,2,3,14
Membrane Cholesterol
The amount of cholesterol differs between types of plasma membranes. Bacteria for example do not have any cholesterol in their plasma membranes. The presence of cholesterol has few but very important functions in the plasma membrane of eukaryotic cells. The cholesterol immobilizes the first few hydrocarbons of the phospholipid molecules; this makes the lipid bilayer less deformable and decreases its permeability to small water soluble molecules. Without cholesterol a eukaryotic cell would need a cell wall (similar to bacteria).1,3,10
10
The cholesterol molecules have the same orientation to the phospholipid molecules. Their polar region is aligned with the polar region of the phospholipids which is the phosphate groups and their non-polar region is aligned with the fatty acids tails (non-polar).1,3,10
Transport across membranes
A phospholipid bilayer around cells makes a very effective barrier between the cell and its external environment. This barrier is particularly effective against water-soluble molecules and ions. The aqueous contents of the cell are thus prevented from escaping out to the external environment. However some exchange between the cell and the environment surrounding it is essential to the cell’s survival. The mechanism used to do the exchange depends on the properties of the substance being transported. There are four basic mechanisms by which exchange of substances are achieved, these are: Diffusion, Osmosis, Active Transport and Endo-/Exocytosis.
Diffusion
Diffusion is the movement of substances from a region of their higher concentration to a region of their lower concentration. Diffusion do not require energy (ATP), it is a passive process. With diffusion substances after a while tend...

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