1 PPISMP SAINS 2014
• Biological membrane that encloses the
cytoplasm/protoplasm of the cell.
• Separate the interior and external of the cell.
• Provides shape & protection.
• Semipermeable or selectively permeable.
• Made of a phospholipid bilayer ;
- Hydrophilic [water liking] face ouside.
- Hydrophobic [water dreading] face inside.
Structure of Plasma
• Proposed by Danielli & Davson in 1953.
• Made of phospholipid bilayer where;
- the hydrophilic [polar] heads facing outside &
coated with protein.
- Hydrophobic [non-polar] tails facing inwards,
sandwiched between two bilayer.
- Structure is stable, static & rigid.
FLUID MOSAIC MODEL
• Also known as Singer Model.
• Proposed by S.Jonathan Singer & Garth Nicolson in
1972 based on their study by using freeze-fracture
• In this model, membrane is a fluid system with
proteins embedded in phospholipid bilayer.
• Composed of : - 2 type of protein [ Integral &
- 2 type carbohydrates [ glycoprotein
& glycolipid ]
• The membrane is a dynamic fluid system with
globular proteins embedded in the
phospholipid bilayer mosaic structure.
• Phospholipid move through the membrane
and flip flopping across it fluidity
• Protein do not coat the membrane surface.
• Thickness of PM: 7.5 nm.
• Phospholipid is the main component of PM.
• Composed of 2 protein ; Integral & peripheral
- Integral proteins > interspersed between
> act as enzymes, pumps, carriers, channels &
- Peripheral proteins > attached to the inner or
outer surface of the membrane.
• Composed of carbohydrates [glycoproteins &
- Glycoproteins ; formed when oligosaccharides
attached to globular proteins.
- Glycolipid ; formed when oligosaccharides
attached to phospholipids.
• Both act as – chemical receptors
- cell recognition
that enable the cells to : (i) recognise each other.
(ii) differentiate themselves from foreign cells.
• Composed of cholesterol – reduce the
membrane flexibility & permeability to the
- Increasing the fluidity.
• PM are semi permeable.
• Small uncharged polar molecules are able to
cross the PM freely.
• Ions & large uncharged polar molecules such
as glucose are not allowed.
Functions of Plasma
• Controls the inflow & out flow of materials to
maintain the internal environment of the cell.
• Separate the cytoplasm from its external
• Act as cell identity marker provided by
glycoprotein & glycolipids.
• Act as receptor for chemicals.
• Helps transporting ions and large, polar
substances into & out of the cell.
• Act as attachment site for cytoskeleton that
maintain the cell shape.
• Play a role in cell adhesion.