2. Every cell has a semi permeable membrane that acts as
a protective covering for that cell from the external
environment.It's microscopic membrane of lipids and
proteins which forms the external boundary of the
cytoplasm of a cell or encloses a vacuole, and
regulates the passage of molecules in and out of the
cytoplasm.
Plasma membrane.
3. Discovery of the plasma membrane
:-
Hartog Jacob Hamburger 1896 Developed Hamburger's
solution and conducted
osmotic studies with
erythrocytes
Charles Ernest Overton 1899 He showed that the
membrane was in lipid
structure, conducted
studies on necrosis and
became the first
"membranenologist".
Nathanson 1904 He proposed the mosaic
membrane theory.
Fricke 1923 He calculated that the cell
membrane only is 4 nm
thick
4. Garter and grendel 1926 It was the first
model of plasma
membrane. He was
the first to create
plasma membrane
in laboratory for the
first time.
Nathanson 1904 He proposed the
mosaic membrane
theory.
Fricke 1923 He calculated that
the cell membrane
was only 4 nm.
thick.
Harvey and Kennet
S. Cole
1932 Suggested the
membrane is
surrounded by
proteins.
James
Danielllis
and Davson
1935 Sandwich
membrane
model
Robertson 1959 Unit
membrane
model
Singer and
nicolson
1972 Fluid mosaic
model
5. Major models of plasma membrane
Garter and grendel model:- it was proposed in1926. By studying the bimolecular layer of lipid in
erythrocytes.in this layer both the polar end are toward and oppositeof the cytoplasm. they also studied the
presence of lipid as phospholipid and cholesterol. It is also called as leaflet model or lipid lipid bi-layer mode.
Davson and Danielli(sandwich model):- in this model
plasmamembarne is madeup of three layers in which
bilayer lipidis sandwiched by a layer of protein
6. Unit membrane model:-Robertson 1959 according to
this model all the cellular and organeller membranes are structurallyand
functionally similar.Plasmamembraneis found in exteriorof cell and cell
organelles.He used mylein sheath to study this.
Fluid mosaic model :Singer and nicolson 1972 it's the
latest and the widely accepted model for the structure of plasmalemma.
Its also called protein ice berg in a sea of phospholipid.
7. This model explains the structure of the plasma membrane of animal cells as a mosaic of components
such as phospholipids, proteins, cholesterol, and carbohydrates.
8. Phospholipids:-
:-Phospholipids is the main component of cell membrane
because it forms the stuctural frame of the cell membrane.:-
Phospholipids layer provides fluidity to plasma membrane because
phospholipids are rich in unsaturated fatty acid which are liquid in nature.
- the quasi fluid nature of the membrane is importance for cellgrowthand
division.
- cholesterolis also present in plasma membranethat is more rigid then
phospholipidsso it helps in stability of the membrane structure.
9. Proteins:- two types of plasma membrane is present in the plasma membrane.
1-Integral or interinsic protein:- These are tightly bound with phospholipids. It can be partially
buried or totally buried. These type of protein are called as tunnel(channel) protein which provide
a passage for movement of water soluble material across the membrane.
2- peripheral or extrinsic protein :- they are superficiallyarranged on the surface of lipid
bilayer.These proteins have enzymatic activity.
10. Transport through plasma membrane :-
The membrane is selectively permeable. Many molecules move briefly across the membrane
without any requirement of the energy and this is called as passive transport. Neutral solutes
move by simple diffusion.
Polar moleculer can not pass throughnon polar lipid bilayer. So the transport is done by a
carrier pprotein.few ions transport across the membrane against their concentration gradient.
( lower to higher concentration).These type requires energy and ATP is utilized in it, its called
active transport. (Na+/K+ pump)
11. Transport between plasma membarne can also be
classified :-
Endocytosis :- can be pinocytosis that is ingestion of liquid through
plasmalemma in the form of vesicle like structure called pinosome.
It can also be phagocytosis that is ingestion of solid material by structure called
phagosome.
Exocytosis :- Egestion of waste material from cell through plasma
membrane.
