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

Thermodynamics of Transport, charged

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 membrane TIM=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