Class on Tuesday, September 22, 2015
Last class I discussed glucose transport into the enterocyte and how it required sodium co-transport. Then later on I was talking about glucose transport into muscle and how it was regulated by insulin. Then a student asked if the transporter in muscle was the same transporter as in intestine. Wow! What a great question! Then a student asked what exactly a glucose transporter was? And this was another great question. So let me answer these two fantastic questions.
The glucose transporter in muscle is in fact a different protein (or gene) than the glucose transporter in intestine. The two proteins are still in the same family of proteins. So what happened is that during evolution these two glucose transporter proteins evolved slightly differently to play different roles. This happened with many proteins in the body.
Below is a table describing five different glucose transporters in the body.
The second question was what are glucose transporters?
Answer: The membranes of the cell is a lipid phospholipid bi-layer that is not permeable to water soluble molecules like glucose. Therefore, there must be a way of getting glucose through the membrane. This is done by a protein transporter that is situated in the membrane (Spans the membrane). In the case of glucose transport into the enterocyte, sodium must be present and co-transported in order for glucose to cross into the cell. This is shown in the following animation:
Here is part of it:
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