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Membrane Transport Mechanisms and Energetics
Fichas del conjunto (41)
- 1Needs for transportMaintain homeostasis
Keep solutes within defined limits e.g. proteins structure impacted by pH
Specific mechanisms for selective transport - 2Intracellular ionic concentrationsExtremely low H+
Very low Ca2+
Low Mg2+
Fairly low Na+
High K+ - 3Solutes in trade and communicationSolutes for growth and maintenance imported and waste exported
Export for wall synthesis/ hormones and other agents
Cells use transport systems to move across membrane - 4Volume regulationRegulate volume through solute movement - water follows by osmosis
- 5CompartmentationAreas of specialised function need own environment different to cytoplasm
Vacuole pH3 - 6Vesicle mediated transportcomponents retrieved, recycled or broken down
New components in place
Endocytosis = pinch of membrane. Import of solids = phagocytosis, liquids = pinocytosis
Exocytosis =addition of new components by fusion - 7Receptor mediated endocytosisMore selective. Cholesterol, growth regulator, iron binding proteins
- 8How does this occur?Specific protein adapter complex interacts with clathrin after specific tetra peptide sequence binds with protein adapter
Clathrin spontaneously polymerises to form coated puts of invaginated membrane below plasma
Protein adapter associates with free end of heavy chain - receptors localised above pits or diffuse into pit region after conformational change when bind to ligand or their solute
Invagination continues until clathrin coated vesicles form
In cytosol, clathrin and adaptors released and recycled, catalysed by chaperone - 9Clathrin3 heavy chains and 3 light chains
From triskelion - 10Cholesterol - unloading the cargoinsoluble - transported as water-soluble LDL
Core of cholesterol ester linked to fatty acids surrounded by phospholipids and unesterised cholesterols
Embedded is specific protein to allow recognition by LDL receptor - 11How uptakes?Uncoated vesicle fuses with CURL - lower pH cause dissociation of LDL from receptor
receptor embedded in CURL extensions, bud as transport vesicles and taken to the membrane
Some transport LDL in lumen, fuse to lysosome. Separated by hydrolytic enzymes - 12ExocytosisFusion of vesicle to plasma membrane to release cargo or insert protein
Seed germination - highly exocytotic - aleurone cells release alpha amylase to hydrolyse starch supply
Marine diatom - able to secrete calcium coccolith - equivalent of human exocytosing tyre - 13Transmembrane transport basicsMore lipid soluble, more permeable
Passive - down concentration gradient for net movement.
increases entropy by dissipating gradient - 14Protein mediated transportHydrophilic, charge, large polar
Passive (facilitated diffusion) - electrochemical gradient. electrical and chemical gradients can be additive (Na+) or oppose (K+)
Active transport -> Carrier, energy from ATP, against gradient - 15Energetics of solutes with no chargeOnly consider concentration different
Exergonic = down concentration gradient
If positive, ATP needed to decrease free energy
Et equilibrium, concentration equal hence Keq =1 - 16Energetics of charged solutesInfluence of membrane potential
Influx of cations favoured
NERNST or Goldman equation
If know Em and find solution concentration different to predicted by NERST, know must be active - 17Membrane potentialsAnimal = -80mV
Plant & Bacteria= -150mV
Fungi = -250mV - 18Partition coefficientIn lipid mediated transport
Amount dissolving in test lipid/ amount dissolving in water
Amount in test lipid equivalent to hydrophobic core - 19Rate limitingCore viscosity - slows movement
Best in liquid crystal state - 20Notable lipid transportEthanol movement for anaerobic respiration of plants and fungi
Lipid soluble vulnerable to hydrophobic pollutants from industrial activities - 21Protein mediated transportProtein undergoes conformational change
Substate same chemical state, but different compartment
Highly specific
Inhibited by similar structures
Rate of reaction quicker - protein lowers Ea
Saturation kinetics
Driven chemical potential gradient of solute
Not intrinsically vectorial - direction depends on gradient - 22CarriersLower Ea of transport
Binding cause conformational change - stop further binding. release at other face trigger return to normal
Cotransport - 23ChannelFastest 10^6-10^8/ sec
Smaller conformational change
Hydrophilic pore - 24Fungi adaptationsPhosphorylate glucose as soon as reach cytoplasm to prevent gradient reversal
- 25Ion transportVaried specificity of channels - size and residues lining pore determine
Gate controlled via +ve charge amino acid residues - voltage sensory. Phosphorylation or cAMP
Channels rapid where needed - nerve/ muscle
Plants - K+ to close stomata - 26Patch clamp electrophysiologyion movement generates electrical current
Glass electrode pushed against to isolate
tiny currents mreasures
Increase of 1Pa for less than 1 sec. 10^-2 moles pass - 27IonophoresBacterial peptides, secreted to kill competing bacteria
Shuttle within membrane
Valinomycin has K+ in centre - hydrophobic outside to allow transport through
Bacteria have beta barrel porins for passive transport - 28Water movementsDiffusion
Bulk flow - down pressure gradient
Osmosis - high energy to low energy - 29Water potentialWP = solute potential + pressure potential + gravity effect (only if above 5m)
- 30Why water potential causes movement of waterAdding solutes increases entropy - WP more negative
Solute potential = -RTcs (Cs mole concentration solute per litre water)
Pressure potential - negative pressure decreases water potential - walled cells- protoplast against inflexible wall and wall pushes back with equal force - 31Osmosis in actionNo significant pressure difference if no wall
Hypotonic, water moves into cell as higher water potential outside
Isotonic = same water potential inside and outside so no net movement
Hypertonic = water moves out as lower water potential outside - 32Growth of walled cellsLoosening of wall needed
Accumulates solute for water to enter
Antibiotics weaken walls - 33How water goes through membraneAquaporins
Regulated by phosphorylation and ADH
Osmosis combination of through membrane and bulk flow through aquaporins - 34Active transportEnergy input form ATP to move against gradient
Primary = ATP directly used to power
Secondary = energy from gradient
Specific, saturation kinetics, solutes can be accumulated against gradient - 35Primary active transportHydrolysis coupled to trnasport
ATP high energy bond to overcome phosphate repulsion
-31kjmol-1 released to decrease Gibbs free energy to make negative - 36P Type ATPaseEukaryotic cell function. phosphorylated intermediate - Na+/K+ ATPase
2K+ in/ 3Na+ out to maintain below toxic
1/2 ATP on this
Phosphorylation releases Na+, removal of P binds K+- conformational change
Plants - H+ transactor. 1H+ per ATP. Maintain pH gradient for cell function - 37V Type ATPaseH+ translocating pumps - ubiquitous in eukaryotes endomembranes - vacuole, vesicles, endosomes
Acidification of compartment. ATP drives. V0 integral domain, peripheral V1 domain - 38Secondary active transportCotransport of glucose - Na+ chemical gradient symports glucose in with Na+
Chemical gradient brings one down and one against gradient
Symport = same direction
Antiport = opposite - 39F type ATPaseUse transport mechanism to synthesis ATP
Plasma bacteria membrane/ inner mitochondrial membrane/ thylakoid membrane
H+ pumped across membrane, chemiosmosis back down gradient stimulates ATP synthesis
similarity supports endosymbiosis - 40Structure of ATPaseSequential H+ binding and release at weak acidic residuals changes electrostatic attraction, rotation by epsilon gamma shaft
3 beta and 3 alpha subunits - beta involved in ATP formation
Each 120 degree rotation causes conformational change and release of ATP - 41Membranes and signallingSignalling ligand recognised by specific transmembrane protein receptors - specific and sensitive
Response without ligand crossing
Ligand binding causes conformational change in receptor - functionally linked to cytoplasmic protein and initiate next reactions
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- (Membranes) Biology of Cells IA Fichas sobre Membrane Transport Mechanisms and Energetics, creado por Alice Hathaway el 08/01/2019.
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- Alice Hathaway
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