Transport Proteins (Campbell Biology)
Specific ions and a variety of polar molecules can’t move through cell membranes on their own. However, these hydrophilic substances can avoid contact with the lipid bilayer by passing through transport proteins that span the membrane.
Some transport proteins, called channel proteins, function by having a hydrophilic channel that certain molecules or atomic ions use as a tunnel through the membrane. For example, the passage of water molecules through the membrane in certain cells is greatly facilitated by channel proteins known as aquaporins. Each aquaporin allows entry of up to 3 billion water molecules per second, passing single file through its central channel, which fits ten at a time. Without aquaporins, only a tiny fraction of these water molecules would pass through the same area of the cell membrane in a second, so the channel protein brings about a tremendous increase in rate. Other transport proteins, called carrier proteins, hold onto their passengers and change shape in a way that shuttles them across the membrane.
A transport protein is specific for the substance it translocates (moves), allowing only a certain substance (or a small group of related substances) to cross the membrane. For example, a specific carrier protein in the plasma membrane of red blood cells transports glucose across the membrane 50,000 times faster than glucose can pass through on its own. This “glucose transporter” is so selective that it even rejects fructose, a structural isomer of glucose. Thus, the selective permeability of a membrane depends on both the discriminating barrier of the lipid bilayer and the specific transport proteins built into the membrane.
Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition. https://www.pearson.com/us/higher-education/series/Campbell-Biology-Series/2244849.html
Date Published: December 5, 2018 Publisher: Public Library of Science Author(s): Hassan Zafar, Milton H. Saier, Luis Caetano Martha Antunes. http://doi.org/10.1371/journal.pone.0208151 Abstract: The communities of beneficial bacteria that live in our intestines, the gut microbiome, are important for the development and function of the immune system. Bacteroides species make up a significant fraction of the … Continue reading
Research Article: In vitro transport of methotrexate by Drosophila Multidrug Resistance-associated Protein
Date Published: October 12, 2018 Publisher: Public Library of Science Author(s): Agnes Karasik, András Váradi, Flóra Szeri, Hernâni Gerós. http://doi.org/10.1371/journal.pone.0205657 Abstract: Methotrexate (MTX) is a widely used chemotherapeutic agent, immune suppressant and antimalarial drug. It is a substrate of several human ABC proteins that confer multidrug resistance to cancer cells and determine compartmentalization of a … Continue reading
Research Article: Polyglycine Acts as a Rejection Signal for Protein Transport at the Chloroplast Envelope
Date Published: December 9, 2016 Publisher: Public Library of Science Author(s): Joshua K. Endow, Agostinho Gomes Rocha, Amy J. Baldwin, Rebecca L. Roston, Toshio Yamaguchi, Hironari Kamikubo, Kentaro Inoue, Xiu-Qing Li. http://doi.org/10.1371/journal.pone.0167802 Abstract: PolyGly is present in many proteins in various organisms. One example is found in a transmembrane β-barrel protein, translocon at the outer-envelope-membrane … Continue reading
Date Published: August 2, 2016 Publisher: Public Library of Science Author(s): Mauro Pietribiasi, Jacek Waniewski, Alicja Załuska, Wojciech Załuska, Bengt Lindholm, Jeff M Sands. http://doi.org/10.1371/journal.pone.0159748 Abstract: The kinetics of protein transport to and from the vascular compartment play a major role in the determination of fluid balance and plasma refilling during hemodialysis (HD) sessions. In … Continue reading
Research Article: Vesicular Location and Transport of S100A8 and S100A9 Proteins in Monocytoid Cells
Date Published: December 14, 2015 Publisher: Public Library of Science Author(s): Paramita Chakraborty, Per Bjork, Eva Källberg, Anders Olsson, Matteo Riva, Matthias Mörgelin, David Liberg, Fredrik Ivars, Tomas Leanderson, Mohammad Saleem. http://doi.org/10.1371/journal.pone.0145217 Abstract: We show here, by using surface biotinylation, followed by Western blotting or surface plasmon resonance analysis, that very low levels of S100A8 … Continue reading