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MEMBRANE STRUCTURE, MEMBRANETRANSPORT
MEMBRANE STRUCTURE
Biological membranes consists of lipids and proteins to bind with non-covalent bond.
Phospholipids are the main components of biological membranes.
Phospholipid = diglyceride (1 glycerole + 2 fatty acids) + phosphate group + organic molecule
(e.g. choline)
Membrane-models
Irving Langmuir was an American chemist and
Lipid-soluble substances enter the cell quickly.
physicist. 1932 – Nobel prize
Fats are arranged in a layer on the surface.
Benzine-lipid mixture, the evaporation of petrol a
molecular lipid film is formed.
Petrol – soluble lipids form lipid bilayer on the surface
of the water.
1925 Lipid bilayer
The proteins are an integral part of cell membrane. The
lipid bilayer. Partly explains the proteins, sugars, ions and
other hydrophilic substances fast passage.
Discovery of Electronmicroscope.
The cells are covered by plasmamembrane.
„Unit-membrane”model.
Mosaic-like
1972
„ Fluid arrangement
mosaic” modelof
proteins in the membrane.
Transmembrane proteins.
Dr. habil. Kőhidai László
FLUID MOSAIC MODEL
Singer – Nicolson
1972
Membrane of erythrocyte
http://www.youtube.com/watch?v=ZP3i5Q9XfTk
http://www.youtube.com/watch?v=oq4Um1oV4ag
STRUCTURE OF THE CELL MEMBRANE
MEMBRANE PROTEINS
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These proteins determine the function of the membranes.
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The types of membrane proteins:
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Transmembrane proteins – It can bind to the hydrophobic part of the
membrane.
Peripheral membrane proteins– not directly linked to the membrane.
Glycoproteins - these oligosaccharides are attached to the extracellular side of
the membrane proteins.
Glycosyl-phosphatidylinositol (GPI) - are covalently bonded to the
membrane’s lipids.
Roles:
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Ion channels
Receptors
Signal transduction
Example 1: DIFFUSION THROUGHT THE CELL MEMBRANE
EXTRACELLULAR
SPACE
MATTER
TRANSPORT
LIPID BILAYER
MEMBRANE PROTEINS
INTRACELLULAR SPACE
cytoplasm
water
apolar molecules
ions
monosaccharides
amino acids
metabolites
different mechanism: exocytosis and endocytosis
DIFFUSION THROUGH THE CELL MEMBRANE
TRANSPORT PROCESSES ACROSS BIOLOGICAL MEMBRANES
I. TRANSPORT MECHANISM
WITHOUT MEDIATOR
WITH MEDIATOR
PASSIVE DIFFUSION
ion channels
1.
2.
FACILITATED DIFFUSION
carrier proteins
carrier proteins
3.
PASSIVE TRANSPORT
4.
ACTIVE TRANSPORT
II. ENERGETIC REQUIREMENTS
DIFFUSION THROUGH THE CELL MEMBRANE
1. PASSIVE DIFFUSION
Passive transport
Without mediator
 direction of transport:ELECTRO-CHEMICAL POTENTIAL GRADIENT
 chemical potential gradient (concentration)
 electric potential gradient (charge)
 rate of diffusion: Fick’s laws
 mediator: no
 energetic requirement: no
 examples:
 hydrophobic molecules: O2, N2
 small polar molecules: CO2, water, alcohol, urea, glycerol
 glucose, sacharose
DIFFUSION THROUGH THE CELL MEMBRANE
2. FACILITATED DIFFUSION
Passive transport
With mediator: ION-CHANNEL
 direction of transport: chemical or electro-chemical potential gradient
 rate of diffusion: faster than that expected from Fick’s laws
 mediator: ION-CHANNEL PROTEIN
 transmembrane proteins
 closed / open state: no transport / transport
 regulation:
 mechanically-gated (mechanical tension)
 voltage-gated (potential difference)
 ligand-gated (ligand-binding)
 selectivity: size & charge of the ions
 energetic requirement: no
DIFFUSION THROUGH THE CELL MEMBRANE
3. FACILITATED DIFFUSION
Passive transport
With mediator: CARRIER PROTEINS
 direction of transport: chemical or electro-chemical potential gradient
 rate of diffusion: faster than that expected from Fick’s laws
 mediator: CARRIER PROTEIN
 specifically binds the ions or molecules and promotes their transport
 energetic requirement: no
DIFFUSION THROUGH THE CELL MEMBRANE
4. FACILITATED DIFFUSION
Active transport
With mediator: CARRIER PROTEINS
 direction of transport: AGAINST the chemical or electro-chemical potential gradient
! ENERGY IS REQUIRED
 mediator: CARRIER PROTEIN
 uniporter
 symporter/antiporter
 energetic requirement: yes
 ATPase transporter (ATP hydrolysis)
 photo transporter (light energy)
 coupled transporter (energy from an other transport)
 example: Na+-K+ pump