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:
http://www.vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/absorb_sugars.html
Here is part of it:
Digestion and Absorption of Carbohydrates, September 18, 2015
In order to learn about nutrition in the body, we need to know about all the different metabolic processes. One can ask the questions, “Is sugar bad for you? If so, why?” As we will find out, these are very complex questions. And we need to know how glucose is handled by the body in order to even come close to answering these questions. Today’s lecture involved a blackboard demonstration of carbohydrate digestion and glucose absorption. I spent a great deal of time on this, but I thought it was important to go through it in detail.
Digestion- What is interesting to me is that both amylose and amylopectin are digested so fast—see their glycemic indices. However, there are versions of amylose that are very long that are more slowly digested because the chain curls up on itself and the enzyme can’t get at it.
Also in the diagram is cellulose, which looks very similar to amylose (long chain of glucose molecules) but if you look closer it uses a different kind of bond (called Beta) that links the glucoses together and human enzymes can not cleave it.
Sucrose is only a disaccharide and it is only half glucose. The other half is fructose.
No matter what, the glucose transporter in the enterocyte requires sodium and there is co-transport of glucose and sodium into the enterocyte cell. Then the glucose enters the blood and flows fairly directly to the liver. The increase in glucose in blood stimulates the secretion of insulin from the pancreas. Insulin is important in removing glucose from the blood. We will go over this in great detail in the next lecture.
Here are some of the figures.
Information on Food Labeling is on the Internet
Information on Food Labeling is easily found on the internet:
Who is in the Class? – In Class Survey on September 1 2015
Who is in the class? This information is important for me and important for you. It is good to see who the competition is. There may be more students of your major in the class than you thought. The class has more seniors than usual, but the seniors have little biology and chemistry in their background. As one student said, “It was either this or Dinosaurs.” I would have taken the class on Dinosaurs myself! The seniors are experienced students and usually do well. There are more freshman in the class than usual. In fall 2014 several freshman did well, so it is possible for freshman to keep up, but it will require more studying for them. As usual, the class is largely made up of sophomores and juniors. As I mentioned in class, “Everyone is welcome!”
Here are the data:
What Part of Genius and Partnership is Required Reading
This year I have assigned a book I wrote as required reading. But I am only requiring that you read Part II. Cholesterol: What is it? One of the reasons I wrote this book was to explain what this mysterious molecule (cholesterol) is and how it is important in the body. I could have written an entire book on cholesterol, but I don’t think many people would have read it! If you get a chance, please read the whole book. It is about Ancel and Margaret Keys. I wrote the book because there are some very untrue accusations about Ancel Keys on the Internet and in some recent books. I can assure you they are totally false, and in fact, Ancel Keys was a great scientist and American.
Note: The Genius and Partnership book can be found as a pdf on the Sakai website!
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