THE LINK BETWEEN OBESITY AND FRUCTOSE METABOLISM

Hey guys this Kim and Kevin here to bring to you part of glycolysis.

I essentially wanted to show you how biochemistry can tie in with real life problems that many people especially children suffer with. OBESITY!

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Obesity contributes to all these factors, not just being obese.

<<<< SAY U LOVE ME LIKE A FAT KID LOVES CAKE! Ok that was a little humour but seriously this is an important issue that is threatening kids’ lives today!

So just to juggle your mind fructose is one of the monosaccharide polymer of the disaccharide sucrose ( table sugar). It is wayyyy sweeter, more soluble than sucrose and inexpensive to produce in the form of high fructose corn syrup. Well you know this just entices manufacturers of sodas and processed foods. However those of you chefs out there that like to sweeten with this and even those who consume these foods concentrated with it, there are many dangers of high fructose corn syrup which are listed below:

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 Alright let’s try to link it to obesity

Obesity is a very serious epidemic. One of the factors that may be contributing to this epidemic is consuming way too much high fructose foods and drinks. So guys you see all those Coca- cola drinks and canned syrups and fruits THOSE ARE A BIG NO-NO! This is essentially what is in 20 ounce glass of coca cola.

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Let me show you why through the explanation of the metabolism of fructose.

There are 2 ways fructose can be metabolised in the body: (which parts of the body do you think these occur?)

  • Adipose tissue, muscle and kidney- the enzyme hexokinase phosphorylates or converts fructose into fructose- 6-phosphate and then enters glycolysis. Below shows the what happens in equation form:

Fructose + ATP ——-à Mg2+  fructose-6-phosphate + ADP

  • Liver- this is the pathway that fructose is primarily metabolised since hexokinase is not present but the enzyme glucokinase. Glucokinase has a low affinity for fructose or basically hates and avoids fructose. Therefore fructose goes through the fructose-1-phospate pathway. Below shows the summary of fructose metabolism in the liver:
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Reasons for high fat storage:

1)      – Fructose is phosphorylated to give fructose- 1 – phosphate by enzyme fructokinase. It’s that easy just remember 1 goes in between fructose and phosphate.

–          Then the fructose- 1- phosphate is then split up by the enzyme fructose-1 – phosphate aldolase into two, 3C molecules ( glyceraldehyde and dihydroxyacetone phosphate) Gosh I know right those words are so long to remember so here’s an acronym for the 2nd one (DHAP)

–          Only one the 3C molecules actually move on to the 2nd stage of glycolysis. Which one do you think it is? Don’t worry if you got it wrong, this question is tricky! It’s DHAP! It can be converted by the enzyme triose phosphate isomerase to glyceraldehyde-3-phosphate and then it continues into glycolysis.

–          However the glyceraldehyde is converted into glyceraldehyde-3-phosphate which is then converted to glycerol- 3- phosphate. And why do you think this latter conversion is bad? Ok let’s try to break it down where have you seen the word glycerol already, not in triglycerides which are mainly lipids(fats). However in this case it contributes to triacylglycerols. This can cause more fat being stored thus more fat + no exercise———à OBESITY

2)      The second reason for the contribution of the obesity epidemic is that:

–          There is a step that fructose metabolism completely bypasses in glycolysis which is the phosphofructokinase-catalyzed step and thus it avoids a major regulatory point.

–          Therefore disruption of the metabolism occurs and there is a greater lipid production or more fat is produced than in glucose metabolism.

–          This is why eating too many high fructose foods result in obesity due to fat storage.

Below shows a summary of the metabolism of fructose as well as glucose which has been discussed before:

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Here is a simpler diagram to follow from:

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So next time you want to pick up that can of coke or partake of  a McFlurry or even Grandma’s sweet homemade cookies just think again before it leads to this:

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Alright see you next time guys, talking to you about this topic has been informative and fun for both you and I. Take care, see you next time!

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REFERENCES:

BOOKS:

Pratt, Charlotte W., and Kathleen Cornely. Essential biochemistry. Hoboken, NJ: J. Wiley, 2004.

WEBSITES:

https://www.ucsf.edu/news/2009/06/8187/obesity-and-metabolic-syndrome-driven-fructose-sugar-diet

http://biochemistrystudy.blogspot.com/2012/10/feeder-pathways-for-glycolysis.html

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