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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