Questions from Students Right Before Exam 2, October 29, 2015

Joseph Dixon ♦ October 29, 2015 ♦ Leave a comment

1. Is there any way you could present what we need to know about the metabolic pathways more clearly?  I’m confused on the ones in the book to how they are presented in the powerpoints.

   Answer: Thanks for your email and question, which is a good one.

   First of all, the chapter in the book is rather weak and confusing.

   When I presented each of the macronutrients, I went over digestion and the distribution of those nutrients throughout the body.

   The formation of chylomicrons in the enterocyte is for the purpose of the delivery of dietary fat from the intestine to many tissues with a final stop at the liver.

   After the above, I presented the metabolic pathways in a very concise way, because my experience with them is that many students do not have the time and background to learn them and integrate them.

   But at the same time, I can’t neglect the metabolic pathways because they show how amazingly easy it is for cells to interconvert the major nutrients-most often in a few enzymatic reactions.  Most of these occur in the liver, which is the body’s metabolic director.

   There are three questions on metabolic pathways on the exam.  There are a few basic questions on the formation ATP using electrons and hydrogens.

   The Key slide in all the Powerpoints is attached (Main Slide in Metabolism Lecture.pptx). And see below. In its bare minimum, what it says for right after a meal is this:
   1) glucose goes to glycogen for storage (pathway #2); 2) glucose goes down glycolysis forming 2 pyruvates (pathway #1), these are decarboxylated and the acetyl CoA can be oxidized (Krebs cycle, #or made into fat (pathway #3).
   2)   After a meal most amino acids are oxidized to CO2 or made into fatty acids (pathway #3).
   3)  After a meal most fatty acids are repackaged into triglyceride and secreted in VLDL;  Very little are oxidized to acetyl CoA

   For 12 hours after a meal the above mainly reverses!   But it important to write these pathways for each of the conditions a few times in order to learn their start and ending points!

   Hope this helps,

Question #2:

The Review Sheet (first paragraph, page 3) indicates that there are “lipid levels you need to know.” Which ones do we need to know?

Answer:  This is left over from a previous year when I required you to know a few lipid values.  I did not do that this semester. You do not need to know specific lipid values.

Question #3:

“I just have a question about the digestion process of Lipids. Where do the step “Bile acids breakup large fat droplets” and “Pancreatic lipase cleaves triglycerides” happen? Are they take place in the small intestine? Or liver?”

Answer:

Thanks for the question.  These digestion steps take place in the lumen of the small intestine. The pancreatic lipase is secreted by the pancreas into the lumen of the small intestine.  The liver is later on. Nutrients are absorbed into the enterocyte, the cell that absorbs most nutrients in the intestine.  Then the nutrients have to leave the enterocyte and move into the blood. For lipids, the dietary fat is packaged into a chylomicron and this is secreted by the enterocyte into the lymph.  Chylomicrons are very large lipoprotein particles. They travel in the lymph until they are dumped into the blood at the thoracic duct.

Question #4:  many little questions–

After studying the lectures I came across a few questions I had:

1) is cholesterol ester a free cholesterol? ANS: Cholesterol ester contains a fatty acid attached to it. You don’t need to distinguish these in this class.

2) from the study guide: which diet had the lowest adherence? ANS: Look this up in the powerpoint!

3) can oleic acid be turned to stearic acid? What are they? ANS: These are both fatty acids – 18 carbons long. Oleic has one double bond. Stearic has no double bonds. Stearic can be turned into oleic in the cell.

4) on the study guide- after one year how much weight was lost on average? In class you said that each diet produced the same weight loss results. ANS: On average about 2-3 kilograms per person.

5) where is VLDL converted to LDL and how does that happen? ANS: In the blood – after much of the triglyceride is removed from VLDL by lipoprotein lipase, what remains is cholesterol, and the particle becomes an LDL. There are many other things that happen. However, some cholesterol is picked up, too. Therefore, LDL is the major carrier of cholesterol in blood!

6)how does LDL enter cells? Does it flow freely in the blood? ANS: It enters via the LDL Receptor. This is discussed in the Powerpoint. There is also a chapter on this in the Ancel Keys book.

7) is the Dr. J and Dr. H referring to omega 6 fats? ANS: The Dr. Jekyll and Mr. Hyde refers to arachidonic acid, because this fatty acid does good things and it may also do bad things in the body. Arachidonic is an omega 6 fatty acid!

The good: It is needed in the brain for neurons.

It also calls immune cells when there is bodily damage.

The Bad: May call and activate too many immune cells, which then attack the body!