Download Plasma membrane Dr.Shayma`a Jamal Ahmed

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At the end of this lecture the student will be able
to:
Define the cell membrane.
Describe the structure of cell membrane.
Determine the functions of cell membrane.
Recognize to the mechanisms of transport.
Compare between the Exocytosis &
Endocytosis
Which is called also plasma Membrane or
Cytoplasmic Membrane .
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It is a biological membrane, it is
surrounding and separating the interior
components (which are alive)of all cells from
the outside environment (which is nonliving).
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 The
cell
membrane is
flexible and
allows a
unicellular
organism to
move.
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Balanced internal condition of cells
Also called equilibrium
Maintained by plasma membrane controlling
what enters & leaves the cell
 Protective
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barrier
Regulate transport in & out of cell
(selectively permeable)
Allow cell recognition.
Provide anchor sites for filaments of
cytoskeleton.
 Provide
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a binding site for enzymes
Interlocking surfaces bind cells together
(junctions)
 Contains
the cytoplasm (fluid in cell)
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The plasma membrane (cell membrane) is
made of two layers of phospholipids. The
membrane has many proteins embedded in it.
The arrangement of protein & lipid molecules
with in the membrane may suggest different
models. The most accepted model is the
Fluid-Mosaic model.
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In 1972, Singer & Nicolson revised the model
in simple way:
They proposed that: the globular protein
are inserted of the lipid bilayer, with their
nonpolar segments in contact with the
nonpolar interrior of the bilayer & their polar
portions stick out from the membrane
surface.
A. Mosaic: an object comprised of bits and pieces
embedded in a supporting structure
1. membrane lipids form the supporting structure
2. membrane proteins provide the bits and pieces
3. both lipids and proteins may be mobile or 'fluid'
B. Membrane lipids: the supporting structure
1. phospholipids
2. glycolipids
3. cholesterol
C. Membrane proteins: the bits and pieces
1. integral (intrinsic) proteins
2. peripheral (extrinsic) proteins
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Lipids : bilayer of phospholipids
Hydrophilic heads - P04 end "water"
"loving" attracted to water on inner/outer
parts of cell
b. Hydrophobic tails - fatty acids "water"
"fearing" attracted to each other on inside
of bilayer
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Diagram of the arrangement
of amphipathic lipid
molecules to form a lipid
bilayer.
The yellow polar head
groups separate the grey
hydrophobic tails from the
aqueous cytosolic and
extracellular environments.
c. Glycolipids - some carbohydrates
attached
to outer lipids (involved in cell to cell
recognition)
d. Cholesterol - regulates fluidity of
membrane
2. proteins: interspersed throughout the
membrane.
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Receptors:- hormones ,neurotransmitters.
Enzymes: - reactions in & out of cell.
Transport :- ions and molecules.
Intercellular junctions.
Cell-cell recognition.
Cytoskeletal and extracellular matrix
attachment.
1- Integral proteins: - inserted into the bilayer
(transmembrane - across
entire bilayer).
2- Peripheral proteins: - on inner & outer surface.
3- Glycoproteins: - carbohydrates on outer
surface.
glycocalyx - outer carbohydrate coat (cell
recognition and identification).
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11- lipids can pass
through the cell
membrane easily.
2- Small molecules and larger
hydrophobic molecules move
through easily.
e.g. O2, CO2, H2O
3- Ions, hydrophilic molecules
larger than water, and large
molecules such as proteins
do not move through the
membrane on their own