Anchoring Proteins in the Phospholipid Phospholipids Bilayer
Nonpolar areas of protein
Moving Molecules into or out of Cells PROTEINS have a key role in transport across membranes I. Passive Transport 1. Always “down” a concentration gradient
1. Single-Pass… Anchors
Polar areas of protein
2. Always involves proteins called A. Channels B. Carriers C. Pores… “porins”
2. Multi-Pass
II. Active Transport 1. Always “up” a concentration gradient 2. Small molecules transported through A. Protein Pumps 3. Large molecules transported by vesicles A. Endocytosis B. Exocytosis
¾ Channels ¾ Pores ¾ Carriers
Moving Molecules into or out of Cells Passive Transport 1. Multi-pass proteins create openings in the membrane
Moving Molecules into or out of Cells - Passive Transport – Channels
Passive transport of 1) ions 2) Sugars 3) amino acids
K+ ion channel
Solute molecule
Passive Transport 1. Channels 2. Carriers 3. Pores
Moving Molecules into or out of Cells Passive Transport – Carriers
Selectivity filter
Facilitated Diffusion in Red Blood Cells 1) Cl- and bicarbonate ions 2) Glucose carrier
Outside cell
Outside cell Side view
Multi-Pass Protein
Transport protein
Top view
Passive transport of 1) Water-soluble molecules 2) Ions
Inside cell
K+
Inside cell
ion
2
Moving Molecules into or out of Cells Passive Transport – Pores
Aquaporins are Water Channels Aquaporin-0
Porin Protein Pleated folds
How do molecules move across membranes?
Major Sites of Expression Comments
Porins are transport channels 1.Allow movement of small molecules Water Ions Organic Wastes 2003 Nobel Prize in Chemistry Aquaporin Water Channels
1. Proteins allow transport 2. Mechanisms of movement through proteins 1. Passive Transport – “down” concentration gradient ¾ Channels, carriers & pores ¾ Diffusion Simple Facilitated 2. Active Transport – “up” concentration gradient ¾ Molecular Transport ¾ Bulk Transport Exocytosis Endocytosis
