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  #1  
Old 07-22-2012
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Biochemistry What happens after 20 min in oral glucose tolerance test?

A 30-year-old healthy woman is undergoing an oral glucose tolerance test. After a catheter is inserted into an arm vein, she is given a drink containing 75 g of glucose. A blood sample is taken every 20 minutes and assayed for glucose and insulin concentrations. Twenty minutes after she drinks the glucose solution, which of the following biochemical findings would be expected?

a) Fatty acids in adipose tissue are mobilized
b) Hepatic glycogen synthesis is activated
c) Hepatic glycolysis is stimulated
d) Hepatic ketone synthesis is increased
e) Kidney gluconeogenesis is stimulated
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Old 07-22-2012
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answer B, insuline triggers glicogen storage, enhacing activation of glicogen synthets enzyme, mmm glucokinase in liver needs a high amount in glucose to activating
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Originally Posted by Fuser00 View Post
answer B, insuline triggers glicogen storage, enhacing activation of glicogen synthets enzyme, mmm glucokinase in liver needs a high amount in glucose to activating
and what about glykolysis?
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mmm well really im not completely sure about B, glycolisis could be stimulated, but the first answer develops in the muscle metabolism by hexokinasa wich has a lesser Km, in higher amounts of glucose, glucokinase in liver is activated, mm could be
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Originally Posted by Fuser00 View Post
mmm well really im not completely sure about B, glycolisis could be stimulated, but the first answer develops in the muscle metabolism by hexokinasa wich has a lesser Km, in higher amounts of glucose, glucokinase in liver is activated, mm could be
I'm not saying B is not correct. But since it says about hepatic glycogen synthesis and C is about hepatic glykolysis - both stimulated by insulin, I'm just asking why did you decide on B
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since anabolic insulin response in carbs metabolism, i think that with 75g of glucose in 20` is easier glycogen synthase activation than glucokinase (higher Km), although are insulin stimulated
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since anabolic insulin response in carbs metabolism, i think that with 75g of glucose in 20` is easier glycogen synthase activation than glucokinase (higher Km), although BOTH are insulin stimulated
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Old 07-27-2012
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Default correct answer :)

Correct answer is b) Hepatic glycogen synthesis is activated

Hepatic glycogen synthesis is activated by elevated concentrations of glucose-6-phosphate. Glucose-6-phosphate is converted via a series of reactions to glycogen.
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Old 07-27-2012
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Originally Posted by Casandra View Post
Correct answer is b) Hepatic glycogen synthesis is activated

Hepatic glycogen synthesis is activated by elevated concentrations of glucose-6-phosphate. Glucose-6-phosphate is converted via a series of reactions to glycogen.
can you please differentiate more between option option B and C????
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Old 07-28-2012
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Correct Answer

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Originally Posted by offpiste View Post
can you please differentiate more between option option B and C????
I'll try Although when I was solving thi squestion I was confused btw B and C myself.

in the official explanation they only said that c) Hepatic glycolysis is stimulated is incorrect bc glycolysis would be inhibited in that patient.

This question comes from usmleconsult.

The way I understand that now is that this patient took a very high dose of glukose so tonz of ATPs were produced which eventually inhibited eg. rate-limiting enzyme of TCA (isocytrate dehydrogenase), which stopped/limited the glycolysis. My only doubt here is: is it possible to synthesize so many ATPs within 20 minutes after getting glucoce? Well, maybe with 75g iv it is possible

If anyone has any other ideas on how to differentiate B and C, feel free to post it here
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Default A possible explanation

In my opinion there is a threshold for activate glucokinase (liver enzime), if we give Iv glucose (75g) the hexokinase(muscle) enzime is earlier activated than glucokinase (20min) this response is also related to Km, hexokinase has lower Km than glucokinase therefore , glucokinase(liver glicolisis) is "more resistant"(low affinity) to glucose and need more glucose to activate, so Hepatic glycolysis isn`t estimulate (not confuse with inhibited) with that amount of glucose, needs higher amount (I dont have exact amount of glucose , but I consider that 75g is not high amount.
If we give glucose , we`ll obtaine Insulin therefore anabolic response eliciting glucose storage (glycogen synthetase). Im not really sure about c) Hepatic glycolysis is inhibited in that patient because Glucokinase (liver) has not direct feedback inhibition.
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Old 07-28-2012
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I think 20 minutes is the main reason why it can't be C.
In the first few minutes, most glucose would fuel glycolysis. However, 20 minutes is a long time for gycolysis to continue, (high amount of ATP which would inhibit glycolysis.) Excess glucose remaining after several minutes = Glycogen synthesis.
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