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9/3/2009
1
Biological
membranes
Biological membrane = cell
membrane
Definition: semi-permeable barrier
between cell and environment; between
different environments in the cell
responsible for different functions
Types of cell membranes:
Cell membrane = plasmalemma (plasma membrane) Inner membranes Nuclear envelope Membranes of smooth and rough ER Membranes of Golgi apparatus Membranes of mitochondrion (inner and outer) Membrane of lysosome Membrane of peroxisome Membranes of different vesicles
!!! All cellular membranes:
Have similar lipo-proteic structure;
Have different properties and functions determined by:
Heterogeneity of membrane proteins;
+
Heterogeneity of membrane phospholipids;
+
Heterogeneity of carbohydrates.
The functions of biological
membranes
Biologic barrier;
Compartmentalization of eukaryotic cells;
Transport of ions and molecules;
Receiving of signals;
Cell connection;
Support for enzymes
(animation)
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Structure of membranes
Lipid bi-layer phospholipids
sphyngolipids
cholesterol
Proteins Integrated
Peripheral
Carbohydrates Glycolipids
Glycoproteins
Lipid bi-layer
Membrane proteins
Integrated proteins
Peripheral proteins
Glycocalyx
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Receptors
Receptor for insulin
Transport through membranes
Passive transport
Simple diffusion of small uncharged molecules
Facilitated diffusion of medium molecules through permeases
Diffusion of ions through ionophores
Active transport
Transport of ions through pumps
Transport of macromolecules by endocytosis, exocytosis and transcytosis
Cytoskeleton
Cell junctions
Occlusion junctions: Tight junctions;
Septate junctions.
Anchor junctions: Using actin filaments - cell – cell (adherent junctions);
cell – cell matrix (focal junctions);
Using intermediate filaments– cell – cell (desmosomes);
cell – cell matrix (hemidesmosomes);
Communication junctions: Gap-junctions;
Synapses.
Examples of junction proteins
Protein Localization Consequences of
inactivation
E-cadherinAdhesion of epithelial cells
Death at stage of blastocyst
N-cadherinAdhesion in synapses (neurons, heart, skeletal muscles, fibroblasts)
Embryo death because of heart failure
P-cadherin Cell adhesion in placenta, epidermis, breast)
Abnormal development of breast
VE-cadherin Adhesion of endothelial cells
Abnormal development of blood vessels
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Cell junctionsCell junctions
Tight contacts Desmosomes
Gap jonctions