7. membran 2010
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Biomolecular Biomolecular Membrane Membrane
Dra Sri Musta’ina, MKes
Functions of Membrane
1. Compartmentalization
2. Selectively permeable membrane barrier
3. Transport phenomena
4. communication and compartment attachment
5. Cell identity and antigenicity
6. Conductivity
The Fluid Mosaic Model
Sheet-like non-covalent assemblies Regulates transport of small and macro-
molecules Controls flow of information between cells
Specific receptors for external stimuli Generation of signals
Cell adhesion for tissue formation. Energy conversion processes- a battery.
- Small platform, composed of sphingolipids, chol & prot
- fluid, more ordered & tightly packed.
- function : regulate membrane functions- Prot : GPI anchored, tyrosin kinase, G
protein fragments, eNOS- Disease : alzheimer, muscular disthrophi,
astme, allergic respons, etc.
Raft clustering.
Transport l I ntas membran
Lipid bilayer
Small hydrophobic molecules: O2, CO2, N2, benzeneSmall uncharged polar
molecules: H2O, ethanol, glycerolLarger uncharged polar
molecules: glucose, amino acid, nucleotides
Plasma membrane is a semi-permeable membrane
Ions: H+, Na+, HCO3- ,
K+, Ca+, Mg2+, Cl- , etc.
Overview of transport mechanismsOverview of transport mechanisms
DIFFUSION (hydrophobic/ lipophilic molecules only): a slow process.
FACILITATED DIFFUSION, uniport (e.g. glucose transporters)
CO-TRANSPORT: symport (same direction) or antiport (opposite directions
ACTIVE TRANSPORTER, against the concentration gradient
CHANNELS, e.g. sodium channel, water channel (aquaporin)
ATP
ADP + Pi
Diffusion : kinetic energy
Diffusion rate: temperature distance
concentration gradienareaDetermined by : molecular size + attribute
solvent characteristic
Simple diffusion : - oxygen
- carbon dioxide- water- uncharged molecules- lipid soluble molecules
OSMOSIS• diffusion of water molecules through a
selectively semipermeable membrane• from hypoosmotic sol to hyperosmotic sol• continues until : equilibrium reached cell destroyed stopped by opposing force
SOLVENT FLOW. Movement of water occurs by one of two
processes.
1. Osmosis
2. Filtration – (Example: urine formation in kidney)
3. Specific Channel
Passage of water molecules through the aquaporin AQP1. Because of the positive charge at the center of the channel, positively charged ions such as H3O+, are deflected. This prevents proton leakage through the channel.
AquaporinAquaporin water channel proteins called Aquaporins (AQP1 & AQP2)
Peter Agre’s experiment with cells containing or lacking aquaporin. Aquaporin is necessary for making the 'cell' absorb water and swell.
Facilitated diffusion
Molecules with low permeability coefficients can go through the membrane faster than normal diffusion process.
Ex : uptake of glucose into erythrocyte. It is rapidly moved across the membrane down
the concentration gradient with the help of a membrane protein called permease.
The velocity of transport is saturablePermease is a multipass transmembrane
protein to facilitate the diffusion of specific molecules across biological membrane.
Facilitated Diffusion: with molecule specific permease
Glucose transporter (permease)
ATP ADP
Transport velocity
External concentration of glucose, mM
Simple diffusion
Facilitated diffusion
Vmax
Half Vmax
Km
Rate
of G
luco
se U
ptak
eTransporters must have a specific binding site for the solute, e.g. glucose. Once they get in the cells, they are usually phosphorylated to go into metabolic pathway and hence the outer concentration of glucose is higher than inside.
Saturable
Facilitated Facilitated DiffusionDiffusion of Ions of IonsThe transmembrane channels that permit facilitated diffusion can be opened or closed. They are said to be "gated”
1. Ligand-gated ion channels. open or close in response to binding a small signaling molecule or
"ligand". (extracellular ligands and intracellular ligands) The ligand is not the substance that is transported when the channel opens.
2. Mechanically-gated ion channels Examples: Mechanical deformation of the cells of stretch receptors
opens ion channels leading to the creation of nerve impulses.
3. Voltage-gated ion channels In so-called "excitable" cells like neurons and muscle cells, some
channels open or close in response to changes in the charge (measured in volts) across the plasma membrane.
ChannelsChannelsVoltage gated
channels
Sodium channel consists of FOUR transmembrane domain, each has SIX transmembrane αhelices, the forth helice is believed to be the voltage sensor.
Potassium channel has ONE molecule of only SIX transmembrane α helices
COOH
COOH
NH
2
NH2
Active transport
Use ATP hydrolysis directly or indirectly (secondary active transport) to move molecules across the membrane against the concentration gradient.
Active transporters are membrane proteins specifically bind and move the molecules across the membrane to a unique direction using ATP hydrolysis as an energy source.
Mainly for ions and chemicals, creating a chemical gradient using ATP energy.
The gradients created maintain many life processes..
Concepts of active transport
TRANSPORTER• specific• conformation changes• slower than Channel protein• 3 tipe : - passive transporter - active transporter - group transporter- Mechanism : - uniporter - antiporter - symporter
Tipe TransporterUNIPORTER1 molekul, searah gradien konsentrasic/ : glukosa transporter
SYMPORTER• tanpa ATP, energi dari gradien • melibatkan 2 jenis molekul • sama dengan kerja pompaarah : sama, c/ : Na+ dan glukosa, di lumen usus-jaringanANTIPORTERarah : berlawanan c/: Na+ dan Ca+, di otot jantung
P-class pump Perubahan konformasi protein yang disebabkan karena proses fosforilasi oleh ATP
F-class / V-class Proton transporting protein (H+).V-class : mempertahankan pH, pada lisosom, dan vesikula lainF-class : di mitokondria, melawan gradien elektrokimia
Indirect active transport
Three types of ATPases: P, V & F.
α αβ β
P-type ATPase
V-type ATPase F-type ATPase
F1 complex
F0complex
V1 complex
V0 complex
1997 Nobel prize of Physiology and Medicine went to Paul Boyer and John Walker for their work on ATP synthase (F type), and Jens Skou for his work on Na-K-ATPase, which uses one-third of the ATP made by ATP synthase.
ATP synthaseProton
pump
P-type: Na+-K+-ATPase, Ca2+ and H+ pump, P means they have phosphorylation and they all sensitive to inhibition.
V-type: inner membrane ATPase to regulate H+ and adjust proton gradients, v means vacuole type for acidification of lysosomes, endosomes, golgi, and secretory vesicles.
F-type: ATP synthase to generate ATP energy from moving the proton across; F means energy coupling factor. There are F1 and F0 subcomplexes: F1 generates ATP, F0 lets H+ go through the membrane.
ABC transporters: ATP-binding cassette protein for active transport of hydrophobic chemicals and Cl-.
Classified according to their protein sequence homology and structures.
P-type ATPase: Ca2+ATPase
Other divalent ion transporters have similar structure with this Ca2+-ATPase and the αsubunit of Na+-K+-ATPase.
NH2
COOH
Ca2+ binding siteAspartate
ATP binding site
ATP
ADP
Ca2+
ABC (ATP-Binding Cassette) transporters: 6 or 12 trans-membrane helices with 2 ATP binding sites, drug or ligand- binding sites yet to be clearly identified.
ATP binding domains
NH
2 COOH
Oligosaccharide chains
P-glycoprotein
R domain
NH
2
ATP binding domains
COOH
Chloride channel: the cystic fibrosis transmembrane conductance regulator,
CFTR, has an extra R domain
Vesicle-mediated transport
Vesicle-mediated transport
- receptor-mediated endocytosis: requires specific receptor/ligand pair
- small pit contains ligand receptors exposed to extracellular space and adaptin and clathrin on the intracellular side (skeleton for vesicle)
- adaptin links receptor (intracellular side) and clathrin to form a coated pit
- clathrin forms polyhedral cage giving the "coat" of the vesicle
- pinching off of vesicle into cell is requires dynamin,a GTPase
- clathrin-coated vesicle is "de-coated" of clathrin and the proteins involved in formation are recycled while the vesicle is further processed
- phagocytosis:ingestion of particles (bacteria, dust, carbon particles)
Vesicular Transport : Receptor Mediated Endocytosis
Junction
A. CELL TO CELL JUNCTION. 1. OCCLUDING JUNCTION / TIGHT JUNCTION 2. ADHERING JUNCTION : actin filament = ZONULLA intermediate filament =
MACULAB. CELL TO CELL COMMUNICATION : gap junctionC. CELL – MATRIX / ANCHORING JUNCTION Not only hold cells together but provide tissues with structural cohesion. These
junctions are most abundant in tissues that are subject to constant mechanical stress such as skin and heart.
1. FOCAL ADHESION / DESMOSOME plasma membrane - plasma membrane of adjacent cells.
2. HEMI DESMOSOME cytoskeleton and extracellular matrix components such as the basal laminae that underlie epithelia
Occluding junction : tight junction
Adhering junction :
a. Zonula adherent
b. Macula adherent
Gap junction
Cell – cell communication
Cell-matrix Adhessive junction : anchoring junction
Desmosome hemidesmosome
Anion antiport in parietal cells of stomach with H+- K+ -ATPase to produce stomach acid.
Basolateral membrane
Apical membrane
CO2CO2
HCO3
Carbonic anhydrase
Cl - Cl -Cl -
HCO3
K+
K+
K+ channel
Anion antiportCl -channel
H+-K+-ATPaseATP
ADP + Pi
K+H2O
+ OH
-
Omeprazole inhibits the proton pump.
Omeprazole and Cimetidine stop stomach acid
• H+-K+-ATPase is an electroneutral antiport. K+ is removed by K+ channel and concurrently Cl- channel removes Cl- to the same direction.
• HCl is the overall transport product in the stomach lumen.
• Omeprazole inhibits the proton pump directly.• Cimetidine resembles histamine to block the
binding of histamine to its receptor thus inhibit the activation of H+K+-ATPase by histamine receptor.
Glucose uptake from lumen to the capillaries using glucose transporter (permease), glucose-sodium symport and Na+-K+-ATPase.
Glucose gets into the cell and
simultaneously transported by
glucose transporter into the capillaries.
Na+Na+Na+
K+K+Na+-Glucose Symport
ATP
ADP + Pi
Na+-K+-ATPase
Glucose transporter: permease
Intestinal lumen
Capillaries
Glucose-NaGlucose-Na++ symport is driven symport is driven
by intracellular by intracellular Na+ levels using Na+ levels using
Na+ –K+ -ATPase. Na+ –K+ -ATPase.
Primary and secondary active transporters work coordinately in animal cells. They generate membrane potential, generate proton gradient, maintain acidity, etc…..
K+
K+
Na+
Na+
Na+
Na+ -driven symport
soluteNa+
soluteNa+ -K+ ATPase
ATP
ADP + Pi
ATP
H+
H+
H+ ATPase
K+ = 140 mMNa+ = 12 mM
K+ = 4 mMNa+ = 145 mM
----
++++
ADP + Pi
Co-transport Systems and Co-transport Systems and their couplingtheir coupling
Adapted from Sperlakis (ed)., 1998. Cell Physiology Source Book. Academic Press.
Na+Na+
Ca-Na Antiport
Ca-ATPase
Ca-channel
Na-K ATPase
Sarcoplasmic reticulum
K+
Na+-K+-ATPase and Ca2+-ATPaseNa+-K+-ATPase and Ca2+-ATPase
Ouabain inhibits Na-K-ATPase.
Ouabains for treatments of angina pectoris and myocardial infarction
Ouabain blocks Na + -K + -ATPase. By blocking the Na+-K+-ATPase, Intracellular Na+ remains high
Hence, the Na+- Ca2+ antiport cannot remove Ca2+ ions out from the cardiac muscle cells.
Eventually, the Ca2+ ion level is restored to maintain the contraction power of cardiac muscle.
MEMBRANE & DISEASES
Can be disrupted by :- Change to protein- component of the lipid bilayer : protein lipid composition- component of cytoskeleton-
Categories of “true” membrane based disease :
1.Defects in cytoskeletal component impair membrane function
2.Altered membrane lipid composition disrupts membrane traficking.
Defects in cytoskeletal component and membrane function :
Ex.-Sickle cell anemiaActin/spectrin lattice “lock”, RBC less drformable and obstruct the microcirculation
- Duchene muscular dystrophyMutation in dystrophin gene disrupts the ability of protein product to anchor cytoskeletal element to the surface membrane. Structural support is loss, membrane becomes permeable, intracell pressure ↑ and cell explodes.
DisrupTs of membrane trafficking
-Rab protein : Lipid modification to carboxyl terminus.
-Hermansky-Pudlak, Griscelly sindrome Lysosome-related organelle
-Niemann-Pick Disease type C (NPC) LSD
Protein membran dysfunctionProtein membran dysfunctionCystic fibrosisDefect pada mekanisme transport chlorida di epitel
paru(CFTR = Cystic Fibrosis Transmembrane Regulator)
Pathologic condition : CFTR transport Cl- : epithelial – airway lumen,
followed by Na+ and water : thick & dehydrated mucous in the lungs
Good breeding ground for infection by bacteria Trouble breathing
Intracellular drug delivery
- Uptake by cell : 1. endocytosis
~ 500 nm
clathrin coated pits
pH environment
2. macropinocytosis, phagocytosis
scavenger (mØ, neutrophils) APC
size : up to the size of cell
- Cross the plasma membrane
- Escape from endosome/lysosome
- Cross the plasma membrane Direct entry to cytosol Viral peptide transporters
- Escape from endosome/lysosome cargo released from vesicle once taken inside the cell routes : - viral peptides evolved for endosomal escape - fusion with endosomal membranes - disruption of endosomal compartments
Intracellular drug delivery (cont)
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