Membrane Transport Proteins
Membrane Transport Proteins - Related Videos
01:34
Protein Transport into the Inner Mitochondrial Membrane
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2023
Nuclear encoded mitochondrial precursors are imported to the inner membrane in a multistep process involving two separate translocons, TIM22 and TIM23. TIM23 is a cation-selective pore that remains closed by the N terminal segment of the protein. Negative charges on the TIM23 act as a receptor for the incoming precursor, pulling the positively charged matrix-targeting sequence for peptide insertion and translocation. Transport of mitochondrial precursors across the TIM23 channel is driven by...
01:18
Protein Transport to the Inner Chloroplast Membrane
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2023
Proteins targeted to the inner chloroplast membrane, or plastid proteins, are transported by two general pathways: the stop-transfer and the re-insertion or post-import pathways. Most plastid proteins carry N-terminal transit sequences and internal import sequences targeting it to the specific chloroplast subcompartment. Proteins targeted by the stop-transfer pathway have internal hydrophobic sequences that inhibit their translocation into the stroma. As a result, these precursors are arrested...
08:46
Green Fluorescent Protein-based Expression Screening of Membrane Proteins in Escherichia coli
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Cited by 34 •
2015
A streamlined approach to screening for the expression of recombinant membrane proteins in Escherichia coli based on fusion to green fluorescent protein is presented.
01:11
Protein Transport to the Outer Chloroplast Membrane
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2023
Chloroplast outer membrane proteins encoded by the nucleus are synthesized in the cytosol. Soon after synthesis, they bind cytosolic factors such as 14-3-3 protein and the Hsp70 chaperones that keep these precursors in an unfolded state until their translocation. Two models describe the mechanism of precursor recognition and entry across the outer membrane through the TOC complex. Model 1 suggests the newly synthesized precursor binds to the TOC receptor 159 and forms a complex.
11:55
Membrane Transport Processes Analyzed by a Highly Parallel Nanopore Chip System at Single Protein Resolution
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Cited by 2 •
2016
The presented protocol describes the analysis of membrane protein mediated transport on the single transporter level using pore-spanning solvent-free lipid bilayers. This is achieved by the creation of bulk produced nanopore array chips, combined with highly parallel data acquisition and analysis, enabling the future establishment of membrane protein effector screenings.
FAQs
Selectivity comes from the chemical fit between a transported solute and the protein’s pathway or binding site. Molecular size and charge help determine whether a solute can enter a channel or bind a carrier, while membrane permeability limits movement through the surrounding barrier. These interactions let cells regulate their chemical composition rather than allowing all dissolved substances to pass.
Channels and carriers differ in how they create a route across the membrane. A channel offers a hydrophilic passageway, whereas a carrier temporarily binds a solute and changes conformation before releasing it on the other side. Pumps add an energy requirement because they move substances against an electrochemical gradient. This distinction explains why transport processes have different energy demands.
An electrochemical gradient combines two influences: a concentration difference and the effect of charge across the membrane. For ions, both factors can favor or oppose movement, so transport direction cannot be predicted from concentration alone. Transport proteins use this combined chemical and electrical driving force, while coupled transport can draw on an ion gradient rather than directly on ATP.
ATP-driven pumping becomes important when a substance must move against its electrochemical gradient. ATP supplies the energy that permits transport in this otherwise unfavorable direction. By sustaining unequal ion and solute distributions, pumping contributes to ion balance and membrane potential, which support cellular function and signaling. This energy dependence distinguishes active pumping from movement through a channel.
A chemistry-focused analysis would compare solute movement with molecular size, charge, concentration difference, membrane permeability, and the presence or absence of an energy source. It would also distinguish direct ATP use from dependence on a coupled ion gradient. These comparisons reveal whether transport reflects passage through a channel, carrier-mediated movement, or active pumping.
They are central when researchers examine nutrient uptake, waste removal, ion balance, membrane potential, or signaling. The same transport principles provide context for studying drug action and transport-related disease. Chemistry connects these outcomes to solute charge, concentration differences, permeability, and energy use, making transport proteins relevant from molecular mechanisms to broader cellular physiology.