4. suppl. membrane transport 2
Post on 18-Jul-2015
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MEMBRANE MEMBRANE TRANSPORTTRANSPORT
Overview of membrane transport Overview of membrane transport proteinsproteins
Uniporter-catalyzed transportUniporter-catalyzed transport
Uniporters accelerate a reaction that is already Uniporters accelerate a reaction that is already thermodynamically favored (similar to enzymes)thermodynamically favored (similar to enzymes)
This type of transport is termed facilitated This type of transport is termed facilitated transport or facilitated diffusiontransport or facilitated diffusion
Three main features distinguish uniport transport Three main features distinguish uniport transport (facilitated diffusion) from passive diffusion(facilitated diffusion) from passive diffusion The rate of facilitated diffusion is much higher The rate of facilitated diffusion is much higher
than passive diffusionthan passive diffusion Transport is specificTransport is specific Transport occurs via a limited number of Transport occurs via a limited number of
uniportersuniporters
A comparison of the uptake rate of A comparison of the uptake rate of glucose by facilitated diffusion and glucose by facilitated diffusion and
passive diffusionpassive diffusion
An example uniporterAn example uniporter
Subunit composition of the Subunit composition of the NaNa ++ /K/K++ ATPase ATPase
Proposed model for operation of Proposed model for operation of the two-Nathe two-Na ++ /one-glucose /one-glucose
symportersymporter
Transport across epithelia: the Transport across epithelia: the intestinal epithelium is highly intestinal epithelium is highly
polarizedpolarized
Transepithelial movement of Transepithelial movement of glucose and amino acids requires glucose and amino acids requires
multiple transport proteinsmultiple transport proteins
Tight junctions seal off body Tight junctions seal off body cavities and restrict diffusion of cavities and restrict diffusion of
membrane componentsmembrane components
Bulk transport: Endocytosis (Pinocytosis, Phagocytosis)
Receptor-Mediated Endocytosis
Protein structure determines Protein structure determines functionfunction
Proteins are single, unbranched chains of Proteins are single, unbranched chains of amino acid monomersamino acid monomers
There are 20 different amino acidsThere are 20 different amino acids A protein’s amino acid sequence A protein’s amino acid sequence
determines its three-dimensional structure determines its three-dimensional structure (conformation) (conformation)
In turn, a protein’s structure determines In turn, a protein’s structure determines the function of that proteinthe function of that protein
All amino acids have the same All amino acids have the same general structure but the side chain general structure but the side chain
(R group) of each is different(R group) of each is different
Hydrophilic amino acidsHydrophilic amino acids
Hydrophobic and “special” amino Hydrophobic and “special” amino acidsacids
Peptide bonds connect amino Peptide bonds connect amino acids into linear chainsacids into linear chains
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