Aston University BIRMINGHAM UK CLOSED OPEN lipid bilayer N selectivity filter in aqueous pore Figure 11-20 Molecular Biology of the Cell 5/@ [C Garland Science 2008) Membrane Transport Zita Balklava z.balklava@aston.ac.uk Learning Objectives To describe: > Membrane permeability. > Membrane transporters and channels. > Driving forces for transport. Aston University
Permeability of membranes How do water-soluble molecules cross membranes? Gases Hydrophobic molecules Small polar molecules Large polar Charged molecules molecules H CO2 O2 Benzene H2O Ethanol Ca2+ Na+ lons Glucose Amino acids TV Aston University Transmembrane proteins facilitate transport Transporters and channels provide specificity (selectivity). v Define which substrates are allowed into the compartment. EXTRACELLULAR FLUID Channel Channel protein Solute CYTOPLASM Transporter/carrier Carrier protein Solute Aston University
Concentration gradients > A difference in concentration (a gradient) represents a chemical potential. barrier C C Diffusion C C C> C=C Aston University Concentration gradients Ć The process is unidirectional! Diffusion C C C C C> C C=C Aston University