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 AF = 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

• 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 membraneTIM=translocase of inner membrane

Post-translational modification

• 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