PSIO 303A Lecture 21: Block 2 - Lecture 6 - General characteristics of membrane transport - carriers and channels_AF
20 Oct 2016
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Block 2 - lecture 6 - general characteristics of membrane transport - carriers and channels. Both facilitate the movement of molecules across the membrane. All channels and some carriers can only support net transport down the electrochemical gradient of their transported substrates. One category of carriers can support net movement of their substrate against an electrochemical gradient (no channel can do this). Carriers are proteins and in some cases they are protein complexes, as they exist as an alternating access pathway (not open/close like channels). They allow particles to go against their concentration gradient. As a consequence of this, they can build gradients where there didn"t exist one. The uptake of substrate (y-axis) into a cell changes as substrate concentration changes (x-axis) At low concentrations, transport increases almost proportional to substrate concentration. However, unlike diffusion as substrate concentration continues to increase, the rate falls over thus reaching a max value. iii.
