When scientists changed the Southern blot to find proteins, they called it a Western blot. When scientists changed the Southern blot to find RNA, they called it a Northern blot. The Western blot is named after the person who invented the Southern blot, Edwin Southern. This means that the scientist can tell whether there is more or less protein but not exactly how much. Scientists say Western blots are semi-quantitative. They will run a Western blot to look for proteins that HIV makes. For example, if a doctor knows a patient is sick and thinks that patient has HIV, the doctor will take a cell sample from that patient. They choose a primary antibody that sticks to that protein. Most of the time, the scientist already thinks they know which proteins are in the sample. Otherwise, the proteins shrink into their tight ball shape again. Scientists put the chemical sodium dodecyl sulfate (SDS) in the gel so the proteins stay unfolded. This makes it easier to tell large proteins from small ones. Denaturing the protein makes it unfold so it is more like a string. A large protein in a tight ball will move faster than a large protein unfolded like a string. Most of the time, proteins are crumpled or squashed into balls or other shapes. Proteins are long chains of amino acids, like beads on a string. Sometimes scientists denature the proteins before the Western blot. This way, the scientists can see how much protein is there on the membrane and where it went when it moved through the gel. The secondary antibody either glows or changes color. The secondary antibody sticks to the primary antibody. Then they treat them with a secondary antibody. The primary antibody sticks to the protein. Then they treat the proteins with a primary antibody. That means they treat them so they will not bind to anything the scientist does not want. Most proteins are clear or cloudy in color, so scientists have to make them easier to see. The scientist puts the rectangular membrane on top of the rectangular gel, so the proteins stay in the same pattern. Next, the scientist moves the proteins from a gel onto a blotting membrane. These are some of the ways a Western blot helps scientists tell proteins apart. Proteins with big electric charges move faster than proteins with small electric charges. Small proteins move through gel faster than large proteins, so they move further. Then they look at the gel to see how far each sample moved. Then the scientist turns off the electrodes so that the proteins stop moving. The scientist or technician waits for some time. The proteins have a negative charge, so they move toward the positive side of the gel as if they are running a race. Then the scientist turns on the electrodes to make a charge. In one row, the scientist puts a mixture of proteins that they already know. They put them in neat rows so they can see which sample is which. So the scientists put the proteins on the negative side of the gel. The other end has a negative electric charge. One end of the gel has a positive electric charge. The electricity makes the proteins move from one side of the gel to the other. They put electrodes on two sides of the gel to make electricity. That means the scientists make a gel in the shape of a rectangle. Scientists studying proteins do Western blots more than any other test.Ī Western blot is one kind of gel electrophoresis. Sometimes a Western blot can show how much of the protein is there. A Western blot can show how big a protein is. Scientists use Western blots to look at proteins. Western blotting is also called immunoblotting. The Western blot is a scientific process. The test proteins are all between 37 and 50 kiloDaltons in size. A complete Western blot that used lipoic acid to show the proteins.
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