transport, con't
DESCRIPTION
Transport, con't. The Na/K ATPase. Consequences of Na/K ATPase. Two ion gradients Used as energy source Electrical signaling Charge difference across membrane Membrane potential difference Negative on inside -60 to –90 mV in animal cells ~ -150 mV in bacteria -200 to –300 mV in plants - PowerPoint PPT PresentationTRANSCRIPT
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Transport, con't.
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The Na/K ATPase
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Consequences of Na/K ATPase
• Two ion gradients– Used as energy source– Electrical signaling
• Charge difference across membrane– Membrane potential difference– Negative on inside
• -60 to –90 mV in animal cells• ~ -150 mV in bacteria• -200 to –300 mV in plants
– Not just due to these ions• Phosphatidylserine on inside of PM• Other ions
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Indirect (secondary) AT
• Na/glucose symporter– Intestinal absorptive cells
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Thermodynamics of Transport
Ain Aout
GA = RT ln ([A]in/[A]out)
if [A]out>[A]in, then G<0 for inward movement
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Thermodynamics of Transport, charged
GA = RT ln ([A]in/[A]out) + ZAF
Z= charge on AF = Faraday's constant, the charge in a mole of electrons = membrane potential, difference in charge between in and out, generally negative
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Intracellular compartments
The Endomembrane System
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Endoplasmic Reticulum
• Smooth ER
• Rough ER
• ER cisternae
• ER lumen
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Smooth ER
• Lipid biosynthesis– Membrane phospholipids– Cholesterol– TAG
• Drug detoxification
• Glycogen metabolism (catabolism)
• Calcium storage
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Rough ER
• "rough" with ribosomes
• Synthesis of – Membrane proteins for endomembrane
system– Secreted proteins
• Initial glycosylation of many of these
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Golgi body
Camillo Golgi, 1898
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Golgi
• Glycosylation of secretory and membrane proteins
• Sorting/trafficking
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Secretory and membrane proteins
• Synthesis starts in cytoplasm on ribosomes
• Signal sequence determines where it goes– Nucleus– Mitochondria
• Post-translational import
– RER (endomembrane system)• Co-translational import
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Pg. 679
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Co-translational import—secreted protein
SRP=signal recognition particle
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Membrane bound proteins
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Post-translational import (mitochondrial)
TOM= translocase of outer membraneTIM=translocase of inner membrane
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Post-translational modification
• Proteolytic cleavage
• Glycosylation
• Phosphorylation
• Addition of a lipid group (lipid anchored proteins)
• Adenylation
• Etc.
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Glycosylation
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The Big Picture
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Bulk Transport
• Exocytosis
• Endocytosis– pinocytosis– Phagocytosis
• Autophagy
– Receptor-mediated endocytosis
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Exocytosis-constitutive
secretion-regulated secretion
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Endocytosis-pinocytosis
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Receptor Mediated Endocytosis
• Bulk transport
• Specific
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The Big Picture
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Coated Vesicles
• Clathrin– Golgi to endosomes– Endocytosis
• COP I
• COP II– ER and Golgi– Within the Golgi
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How do coated vesicles go to the right place and fuse with the
right membrane?
The “SNARE” hypothesis
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SNARE
• Vesicle-SNAP-receptors (v-SNAREs)
• Target-SNAP-receptors (t-SNAREs)
• SNAP=soluble NSF attachment proteins
• NSF=N-ethylmaleimide-sensitive factor
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Lysosomes
• Digestive enzymes
• Low pH (4-5)
• Develop from late endosomes/hydrolases from Golgi
• Activated by lowering the pH
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