Transcript Transport, con't.

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