Biological membranes

9/3/2009
Biological membrane = cell
membrane
Biological
membranes
 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
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!!! All cellular 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
The functions of biological
membranes
 Biologic barrier;
 Have similar lipo-proteic structure;
 Have different properties and functions determined by:
 Heterogeneity of membrane proteins;
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 Heterogeneity of membrane phospholipids;
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 Heterogeneity of carbohydrates.
 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
Glycocalyx
Membrane proteins
 Integrated proteins
 Peripheral proteins
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Receptor for insulin
Receptors
Transport through membranes
Cytoskeleton
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
Cell junctions
 Occlusion junctions:
 Tight junctions;
 Septate junctions.
 Anchor junctions:
 Using actin filaments -
Examples of junction proteins
Protein
E-cadherin
N-cadherin
 cell – cell (adherent junctions);
 cell – cell matrix (focal junctions);
 Using intermediate filaments–
 cell – cell (desmosomes);
 cell – cell matrix (hemidesmosomes);
 Communication junctions:
 Gap-junctions;
 Synapses.
P-cadherin
VE-cadherin
Consequences of
inactivation
Adhesion of epithelial Death at stage of
cells
blastocyst
Adhesion in synapses Embryo death because
(neurons, heart,
of heart failure
skeletal muscles,
fibroblasts)
Cell adhesion in
Abnormal development
placenta, epidermis, of breast
breast)
Adhesion of
Abnormal development
endothelial cells
of blood vessels
Localization
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Cell junctions
Tight contacts
Cell junctions
Desmosomes
Gap jonctions
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