cell membrane
introduction
cell membrane is also called plasma membrane or cytoplasmic membrane
definition :-
cell membrane is the selective permeable membrane so it controle the exchange of material between the cell and environment.
cell membrane separate the cell contents from their external environment.
location :-
cell membrane is the outer most layer of animal cell ,while in plant it lies next to cell wall.
cell membrane is present in all types of cell including pro-karyotic and eukaryotic cells .
characters :-
it is thin , elastic and semi-permeable.
b) chemical composition :-
chemically cell membrane is composed from protein , lipids ,and carbohydrates.
they are present in various ratio.
1)protein :-
Protein is present in high concentration in plasma membrane.
protein made the cell membrane more semi permeable.there are two types of protein is present in cell membrane.
a)pheripheral protein :-
pheripheral protein are also called extrensic protein .They protein which are floating in lipid bilayer or not fully embedded protein are called pheripheral protein.they are present on surface maybe outside or maybe inside the plasma membrane.
b)integral protein :-
integral protein are also called intrensic protein.the fully embedded protein are called integral protein.its function is carrying of protein and enzymes.
2)lipids :-
cell membrane are actually composed of lipids .lipids are structural unit of cell membrane.the major classes of lipids are present in plasma membrane like phospholipid,sphangiolipid,glycolipid,and cholestrole.
phospholipid arranged in bilayer and make up the basic fabrics of plasma membrane they are hydrophobic and hydrophilic.
3)carbohydrate :-
carbohydrate are present on the surface of plasma membrane maybe branched or unbranched .sometimes carbohydrate attach with lipid form gylcolipid and attach with protein form glycoprotein.
4)enzymes :-
about 30 different enzyme are present on the surface of plasma membrane.
enzyme of plasma membrane maybe ecto or endo.
chemical composition of RBC:-
protein ------52%
lipids----------40%
carbohydrate-8%
Ameoba cell :-
protein --------------52%
lipids------------------40%
carbohydrates-----8%
c)models about structure of cell membrane :-
different models are presented about structure of cell membrane, which are given as under.
a)harvey and cole 1932
Harvey and cole in 1932 presented a model about the structure of cell membrane.
they reported the extension of the plasma membrane and suggested the protein in plasma membrane.
b)sandwich model :-
Danille and davijan in 1969 proposed a model about the structure of cell membrane .they gave name to this as sandwich model.
they said that the lipids arr sandwich between proteins they are covalent in nature.
c)fluid mosaic model :-
who presented -
singer and nicolson presented a model about the structure of cell membrane in 1972.
according of this model
"cell membrane is a lipid bilayer in which some protein are completly embedded (intrensic protein) while some protein are partailly embedded (extrensic protein).
the phospholipid bilayer form a fluid in which specific protein fload like ice berg.
the word mosaic refers to the many different kind of protein dispersed in the phospholipid.
each phopholipid molecule has a polar head that are located over the cell surface,which are hydrobhlic ( hydro-water , philic-mean loving) its mean head is atracted to water.
tail of both layer are hydrophobic (phobic mean water hating) theyare repelled by water.
carbohydarte are also prsent in cell membrane in the form og glycolipid and phospholipid.
due to continously changing position of the sheet like structure it was named as fluid mosaic model .
it was the most acceptable model the structure of plasma membrane.
diagrame
cell membrane of egg (ovum)
some special cell posses impermiable plasma membrane like egg through which no molecule can pass only gasses pass through it.
function :-
give protection
cell membrane protect the inner cell content .
separate inner content
seprate inner content of cell from external environement
give shape
give shape to the cell .
regulate matetial
regulate inflow and outflow of matrtial
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