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The aquaporin water channels essay writer of my talk, the aquaporins, is something that we have been studying in our lab for the last 15 years. It is not something that I anticipated when starting my career. In fact, I am a hematologist, but in science, sometimes what we find is not what we are looking for.
A typical middle-aged man, I weigh 75 kg, of which 50 are water. This is something that we all share. Water is the major component of all our cells in all of our tissues. This is also shared with all other life forms, other vertebrates, invertebrates, microorganisms, and plants.
Multicellular life comes with potential problems. One of these problems is the movement of fluids across biological barriers, and the principal barrier for most of our tissues is the plasma membrane.
The aquaporins, which I will describe, are an answer to how water crosses biological membranes, but specific questions still need be defined. I am very pleased to be speaking to the American Thoracic Society because I believe that many of the questions related to fluid movements in lung are still unsettled.
When we began our studies some years back, the problem of membrane water permeability had already been looked at by a generation of biophysicists and physiologists. With the discovery of the lipid bilayer in the s, it was speculated that a finite degree of water permeability would occur by simple diffusion through the plasma membrane.
However, the work of very vigorous biophysicists and physiologists indicated that in certain tissues—for example, renal tubule, secretory glands, and red cells—the water permeability is much larger than could be explained through simple diffusion through the plasma membrane.
And these investigators predicted correctly that there must be specialized water-selective channels in these membranes. The current view is that both mechanisms occur—diffusion through all membranes and flow through aquaporins that are present in certain special membranes.
The biophysical differences are quite significant; diffusion is a low-capacity bidirectional movement of water, whereas water channels have a high capacity and great selectivity for water. The channels are so selective that water passes through them, and acid does not. As we all know, protons exist in fluid as the hydronium ion.
This distinction is really quite important. Every day, our kidneys filter and reabsorb about L of water. If we do not reabsorb that water, we would die of dehydration. If we reabsorb the water, along with protons, we would become systemically acidotic.
The movement of water through the aquaporins is driven by osmotic gradients. For example, red cells dropped into seawater will shrink because water leaves the cells; red cells dropped into fresh water will swell and explode since water enters the cell.
The process of osmosis that we all learned about as children is known to occur very rapidly in membranes in which aquaporins are present. An experiment by Bob Macy at the University of California, Berkeley, in made a very important observation.
It was known that diffusion of water through membranes is not inhibited by any known pharmacologic agents. Macy discovered that mercuric chloride reduces the water permeability of red cells, and when the membranes have been treated with reducing agents, the water permeability was restored.
Macy concluded that the water channel protein must contain a free sulfhydryl somewhere within the pore. This provided very strong evidence that water channels must exist; however, most physiologists and other scientists remained very skeptical. They could not identify water channel molecules, much less purify them, clone them, express them, or reconstitute them.
Our laboratory got into the water channel field by accident. Interestingly, it was identical to a polypeptide in the kidney. This was in the early days before the genome was sequenced, so it was a lot of hard work.
We obtained a cDNA encoding a —amino acid polypeptide. Identical transcripts were obtained from red cell and kidney libraries. The new protein was found to have six bilayer-spanning domains. The N-terminus of the protein resides within the cell, and then two interesting repeats appear, each corresponding to three bilayer-spanning domains.
They are not a perfect sequence repeats but are genetically similar sequences.Aquaporin water channels essay writer, show creative writing groups minneapolis a written curriculum vitae, creative writing course manchester.
Morten Ø. What to write for my college essay Newton's laws and cause and. International Journal of Molecular Sciences, an international, peer-reviewed Open Access journal International Journal of.
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Aquaporins selectively conduct water molecules in and out of the cell, while preventing the passage of ions and other solutes. Also known as water channels, aquaporins .
Oct 19, · Reprinted by permission from King LS, Nielsen S, Agre P. Aquaporin-1 water channel protein in lung: ontogeny, steroid-induced expression. We would like to show you a description here but the site won’t allow us. Aquaporin water channels essay writer Aquaporin water channels essay writer theatre royal sydney death of a salesman essay citation introduction words for an essay tufts application essay dbq essay search and seizure viking invasion of england essay writing a trip to london essayist underbelly season 1 cast comparison essay critical essay on.