What is the pupose of phosphorylating glucose in cytosol?

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bratwurst
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What is the pupose of phosphorylating glucose in cytosol?

Post by bratwurst » Sat Jul 09, 2005 11:44 am

hello !

... there are tree possibilities:

1) to trap glucose in cell
2) destabilize glucose
3) converts it into a better soluble form...

who knows the answer ???
for me all answerst sound great! ... but which one is right?

thx ;)

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victor
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Post by victor » Sat Jul 09, 2005 12:00 pm

I think the answer is (3).
Glucose is phosphorylated become:
Glucose-6-phosphate
Fructose-6-phosphate
Fructose-1,6-diphosphate
then it converted into two molecules of:
Phosphoglyseraldehyde
1,3-diphosphogliserate
3-phosphoglyserate
2-phosphoglyserate
Phosphoenole piruvic
Piruvic acid------(2 molecules)

then these two molecules of piruvic acid get in to oxidative decarbocillation and then Krebs.
Hope this helps. :)
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Post by bratwurst » Sat Jul 09, 2005 12:20 pm

biochemistry 5th stryer...

(1) glucose 6-phosphate cannot diffuse through the membrane, because of its negative charge
---> trapping glucose in cell

(2) the addition of phosphoryl group begins to destabilize glucose...


seems that the first two answers are right...

but as you said the last answer seems
to be right too:

because it has a negative charge = polar ===> more soluble in aquaous environment???? is that right... so maybe all answers are right... LOL ....

greetings ;)

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victor
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Post by victor » Sat Jul 09, 2005 12:39 pm

Um...Glucose-6-phosphate doesn't diffuse??well, I think that the phosphorilation of Glucose is changing glucose into 2 molecules of piruvic acid that have a smaller structure so they can diffuse through membrane..not making the glucose-6-phosphate and diffuse it right into membrane...I think the membrane that you're talking about is the membrane of mitochondria right??
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Post by bratwurst » Sat Jul 09, 2005 1:00 pm

hmm.... so only the 2 pyruvat molecules diffuse into the mitochondria... the glucose-6-phophate is trapped in cytosol....

ok thx....

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Post by Jelanen » Sat Jul 09, 2005 1:56 pm

The answer is 1. Glucose doesn't diffuse through cell membranes, its transported. There is a transmembrane transporter for glucose, but not for glucose-1-P. Phosphorylating glucose locks it into the cell, preventing it from escaping. Adding a phosphate does nothing to help the solubility of glucose. A carboxyl group and 4 alcohol groups does that nicely. Yes, it does begin to destabilize the glucose, but its secondary to the locking it in the cell function.
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Post by Poison » Sat Jul 09, 2005 7:21 pm

Answer: 1
If you do not phosphorylate glucose, it can go out of the cell, but if you do it can not. Means you trap glucose.
It seems that Jelanen gave a better answer. I promise I will read the posts before posting mine :)
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Post by bratwurst » Sun Jul 10, 2005 4:09 pm

yes... lets say answer 1 is right ;) ....

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Post by MrMistery » Sat Jul 16, 2005 8:46 pm

Defiinetly answer no 1. The permease which transports glucose is so specific, that not only it can tell the difference between glucose and glucose-6-phosphate, but it can tell the difference between the optical izomers of glucose: D-glucose can pass, L-glucose can not pass...
A little off-topic, but never the less very interesting
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Post by xand_3r » Sat Aug 06, 2005 4:11 pm

Nice one MrMistery, but you can also say Please UGA of Please UAA. Glucose is actively transported everywhere in the organism, only pentoses (carbohydrates with 5 C atoms, eg ribose) are absorbed passively. Glucose absorbtion in the intestin is coupled with the Na transport , and it's also totally reabsorbed in the proximal region of the urinifer tube. Phosphorilating glucose increases in a small way its solubility in polar solvents like water but it doesn't have any effects on its solubility in the cell membrane wich is composed by phospholipids and its permeable only for liposoluble substances like cortisol and other cholesterol based hormones. Hidrosoluble substances like glucose can only pass through special protein tunnels, when they couple with specific receptors. So, like Jelanen said, phosphorilating doesn't have any effects on the glucose solubility through the membrane, on the contrary it makes glucose unrecognizable for the specific receptors on the surface of plasmalema.

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Post by sdekivit » Sat Aug 06, 2005 6:01 pm

another important thing to hold in mind is the before catabolism can occur, you must put energy in the to metabolizing molecule. This is done by converting glucose to fructose - 1,6 - bisphoshate. The the catabloism can occur, because the phosphate contains energy that can be stored for ATP-synthesis in the last step of the glycolysis. And what is the efficacy when you put some energy in converting a molecule if it's wasted by simple diffusion out of the cell?

Bt the answer to this question is, it can't be said enough, answer 1.
Last edited by sdekivit on Sat Aug 06, 2005 6:05 pm, edited 1 time in total.

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Post by sdekivit » Sat Aug 06, 2005 6:03 pm

bratwurst wrote:biochemistry 5th stryer...



great book :D

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