2012 transport in organism
TRANSCRIPT
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Transport in organism
Transports
Transport across membranes
Electron transport
Nutrient transport
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Transport across membranes
Biological membranes
Composition: lipid bilayer (glycerolphospholipids, cholesterol,
glycosphingolipids, proteins)peripheral and integral
Cell protection and building function, compartmentization
Highly selective permeability
Regulation of metabolic pathways
Impermeable to ions and polar molecules
They can have specific receptors for signal molecules
In some of them are integratet enzymes or enzymes systems
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Basic function of all membranes is
selective transportacross them
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Mechanism of transport
Nonmediated transport
Nonspecific permeationsimple diffusion
Mediated transport
Passive (facilitated diffusion)
Active, against concentration gradient
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Simple diffusion
The direction of movement of solutes by
diffusion is always from a higher to a lower
concentration and rate is described by Fick
Ficksfirst law of diffusion:
A net movement of molecules from onecompartment to another will continue until the
concentration in each is at a chemical equilibrium
Solution in membrane lipids and redistribution on the reverse side
of membrane (some lipophilic compounds, gases dissolved in
waterO2, N2, H2, CO2)
Permeability through irregularity in lipids bilayer(ca 10% of H2O)
Diffusion by pores in membrane
Movement by hydrophilic channels
gap junction
konexin
transfer of molecules and ions between 2 neighbouring cells
Simple diffusion
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Mediated transport
ActivePassive
Mediated transport
Passive
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Ionophores - mediated transport
Ionophores- organic molecules with different structure, often antibiotics,they increase membrane permeability for some ions
- passively transport ions via membrane until the concentration
in each side is at a chemical equilibrium
Ionophores
Valinomycin(cyclic peptide) Transfer of K+(104ions / s)
Gramicidin (linear peptidehelix)
Transfer of K+(107ions / s)
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Glucose transport into
muscle and fat cells
Glc binds to the protein on one face of the membrane
A conformational change closes the first binding site and expose
the binding site on the other side of the membrane
Glucose dissociates from the protein
The transport cycle is completed by the reversion of the glc
transporter to its initial conformation in the absence of bound glc
Glucose transport into
muscle and fat cells
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Membrane channels
Passive, but specific systems
Mainly for cations
Transport due to concentration gradient or gradient of electrochemical
potential
Some channels are always open(eg. some porines)
Mostly regulated:
by membrane depolarization
(ions channels for K+a Na+in nerve impulses) by binding of specific ligand (eg. acetylcholin - neurochemistry)
by mechanical pressure (ions channels in special cells of inner ear)
Gate is principal regulator, open and closed position
Mediated transport
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Mediated transport
ActivePassive
Mediated transport
Active
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Significance of the active transport
Maintain intracellular volume
Maintain ion composition (optimal osmotic condition
in a cell)
Form and keep ion gradient
Elimination of waste products of metabolism
Active transport
Transport against gradien (chem., el.)
Supply of energy is needed
Hydrolytic cleavage of molecules with high transfer
potentialATP
Primary active transport
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Na/K-ATPase
Energy 1 ATP
transfer 3 Na+and 2 K+
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Primary active transport:
Na/K-ATPase
in
out
ATP 3 Na+
3 Na+2 K+
2 K+ADP Pi
Ca-ATPase
Actively pumps Ca2+out of the cytosol at the expense of
ATP hydrolysis Activation by calmodulin
H,K-ATPase of gastric mucosa
Secretion of H+ - antiport with K+
Cl-for HCl formation is transfer by different transportervia symport with K+
Primary active transport
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Secondary active transport
Many active transport processes are not directlydriven by the hydrolysis of ATP
Characterization by co-transport
Antiporter
Symporter
Secondary active transport
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Transport in mitochondrion
Structure of mitochondrion
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Mitochondrial membrane inner membrane
76 % proteins 24 % lipids
in compar ison wi th:
Hepatocytes membrane
46 % proteins 52 % lipids Erythrocytesmembrane
49 % proteins 43 % lipids
MI membrane - outer
Outer membrane contains protein porin,
nonspecific pores
transport of molecules (up 10 kDa) by
diffusion
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MI membrane - inner
High content of proteins - enzymes and transportproteins
permeable only for O2, CO2, H2O
impermeable for acetyl-CoA, oxaloacetate,nikotinamide nucleotides,...
other metabolites (low-molecular products andsubstrates) and some ions have regulatedpermeability
NADH produced by glycolysis must be transported into
MI
metabolites formed in MI (eg. oxaloacetate, acetyl-CoA)
must be transported into cytosolbiosynthesis
ATP formed in MI must be transported into cytosol,
where is most reactions which use it
ADP and Pimust be transported from CY intoMI
(substrates of oxidative phosphorylation)
Mitochondrial transport systems
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Malate-aspartate shuttle
Transport of Ac-CoA to cytosol
Acetyl-CoAoxidative decarboxylaion of pyruvate, FA
oxidation
Low consumption of ATPacetyl-CoA is stored in formof fattransport to cytosol is needed
Acetyl-CoAenters into cyt. as citratetransport
system for tricarboxylic acids
in cytosol:
ATP + citrate + CoA acetyl-CoA + oxaloacetate + ADP + Pi
ATP-citratelyase
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