EEOB 410 Summary of the mechanisms by which substances cross the plasma membrane SEQ CHAPTER \h \r 1 Handout to accompany lecture on Chapter 4 Process Requires integral membrane protein? Type of energy required? Can oppose thermo-dynamic equilibrium? Shows high chemical specificity? Typical molecules transported Simple diffusion via lipid bilayer No None (passive) No No Lipd soluble (usu. small, nonpolar): O2, CO2, short-chain fatty acids, Water at low rate Simple diffusion through a protein channel Yes None except to synthesize channel No Yes Ions: Na+, K+, Ca2+ Water via aquaporins Facilitated diffusion Yes None except to synthesize channel No Yes Small- to medium-sized polar molecules: glucose, amino acids, etc. Primary active transport Yes ATP Yes Yes Ions: Na+, K+, Ca2+, H+, etc. Secondary active transport Yes Ion gradient (often Na+) created using ATP Yes Yes Small- to medium-sized polar molecules: glucose, amino acids, some ions
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