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The cell-surface membrane is the name given to the plasma membrane
that surrounds cells and forms the boundary between cell cytoplasm and
the environment
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some proteins never extend completely across the bilayer
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Some are protein channels (form water soluble ions to diffuse across the
membrane) or carrier proteins (bind to ions or molecules like glucose and amino
acids, then change shape in order to move these molecule across the membrane)
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They are important components of cell-surface membranes because:
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Act as channels transporting water-soluble substances
across the membrane

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Allow active transport across the membrane through carrier proteins

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Act as receptors (like hormones)

Structure of the Cell

the hydrophilic heads of both phospholipid layers point to the outside of
Surface Membrane
the cell-surface membrane attracted by water on both sides
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Phospholipids:
Lipid soluble material moves through the membrane via the phospholipid portion
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allow lipid-soluble substances to enter and leave the cell

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Make the membrane flexible and self-sealing
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The
add strength to the membranes
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Functions:
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Make the membrane less fluid at high temps

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Glycolipids:
Made up of a carbohydrate covalently bonded with a lipid
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Functions:
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Help maintain the stability of the membrane

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In general most molecules do not freely diffuse across it because many are:
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Too large to pass through the channels in the membrane
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Electrically charged (are polar) and therefore have difficulty passing through the
non-polar hydrophobic tails in the bilayer
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These glycoproteins also act as cellsurface receptors (for hormones and neurotransmitters)

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This gives the membrane a flexible structure that is constantly changing
shape
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Mosaic = because the proteins that are embedded in the phospholipid bilayer
vary in shape, size and pattern in the same way as tiles in a mosaic
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act as recognition sites

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Allows cells to recognise one another, for example lymphocytes
can recognise an organisms own cells

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