2012 transport in organism

8/12/2019 2012 Transport in Organism

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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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2012 transport in organism

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