glucose absorption

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raghda
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glucose absorption

Post by raghda » Thu Oct 11, 2007 1:14 am

Hi everyone
sorry I don't know where I put my question :oops:
someone tell me how sodium- dependent glucose transporter SGLT binds to glucose to carry through the plasma membrane to the cytoplasm of cells

and I need textbook of Biochemistry ,which one?!
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Post by kotoreru » Thu Oct 11, 2007 10:14 am

Sorry, can't help on the glucose part but I can recommend a textbook - Biochemistry by Lubert Stryer.
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Post by MrMistery » Thu Oct 11, 2007 5:05 pm

Lehninger Principles of Biochemistry is also good.

Here is how the glucose-sodium transporter works.
You are at the outside of the cell. one glucose molecule and two sodium molecules bind onto the outside of the cell.in this moment, the glucose transporter changes its conformation so that it exposes both the sodium molecules and the glucose molecules on the cytoplasmic side of the membrane. now, because of the concentration gradient, the sodium molecules and the glucose molecule come off the membrane. But now, the protein has all 3 binding sites exposed. in this state, it changes to a 3d conformation with the binding sites on the outside, ready to transport another glucose molecule by the aid of the sodium molecules.
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Post by raghda » Fri Oct 12, 2007 1:09 am

this means that energy is required to pump the sodium out off the cell ,so it's considered active transport method . isn't it?
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Post by MrMistery » Fri Oct 12, 2007 11:03 am

yes it is. Biochemistry books will define two types of active transport:
1. primary active transport - uses the energy from the hydrolysis of ATP directly to pump a substance against its concentration gradient - the Na/K pump is an example
2. secondary active transport - uses energy under the form of a gradient. It is then necessary to create such a gradient by primary active transport - the glucose/Na simporter is an example

However, in the case of the Na/glucose simporter, ATP is NOT used to generate the sodium gradient. there is already a lot of sodium on the outside, which comes from your food.
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Post by raghda » Sat Oct 13, 2007 12:41 am

I wonder if the 2 types of active transport occur in the same time ?
for me, NO as you said
MrMistery wrote:
in the case of the Na/glucose simporter, ATP is NOT used to generate the sodium gradient. there is already a lot of sodium on the outside, which comes from your food.

so it depends on the amount of sodium isn't it?
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Post by Jammerz » Sat Oct 13, 2007 5:35 am

The Na/glucose symporter uses the sodium gradient created and maintained by the Na/K pump, which is a primary active transporter and uses ATP.

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Post by raghda » Thu Oct 18, 2007 10:45 pm

hello people!
I and my collages have serious argument on the number of sodium molecules is it one or two ?
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Post by Jammerz » Thu Oct 18, 2007 11:46 pm

Number of sodium molecules in what?

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Post by raghda » Sat Oct 20, 2007 10:01 pm

the sodium molecules which bind with SGLT
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Post by lara » Tue Oct 23, 2007 8:20 am

it is done by another Na K pump

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Post by MrMistery » Tue Oct 23, 2007 9:43 am

@raghda
Both you and your peers are correct.
There are 2 isoforms of the SGTL.
SGTL1 is located in the small intestine and in a very small proportion in the nephron proximat tubule. It binds 2 Na molecules for every glucose molecule. Since this one is the example in most biochemistry books, some lazy professors will tell you that this is the case for all SGTL - which is wrong
SGTL2 is located in the proximal tubule of the nephron, where it handles something like 99% of the glucose transport. It binds 1 molecule of Na for every glucose molecule.

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