Bio Question Glucose concentrations

[kov82]

Advertisement - Members don't see this ad

On one part of a chapter, I read that Glucose is quickly used up after being taken into the cell so there is always a concentration gradient favoring glucose entry into the cell, but in the same chapter I read the example of secondary active transport that says Na+ enters the cell with its [] gradient through simple diffusion after its kicked out by Na+-K+ pump, when entering the cell it brings in glucose against its [] gradient, so which is it? is glucose immediately used up? or not? are the two statements contradicting one another or they are both correct depending on the situation?

 

[FutureInternist]

On one part of a chapter, I read that Glucose is quickly used up after being taken into the cell so there is always a concentration gradient favoring glucose entry into the cell, but in the same chapter I read the example of secondary active transport that says Na+ enters the cell with its [] gradient through simple diffusion after its kicked out by Na+-K+ pump, when entering the cell it brings in glucose against its [] gradient, so which is it? is glucose immediately used up? or not? are the two statements contradicting one another or they are both correct depending on the situation?

I think the first example is of G going from bloodstream into the cell whereas the 2nd one sounds like going from intestine into blood stream.

When the G goes into the cell it is immediately converted to G6P which is a different compound hence you always have less G inside a cell than in the blood.

Going from intestine to blood however, there is a bunch of free floating G so after a while the intestinal G & blood G even out...how to get the rest of the G into the blood....Expend some energy, pump out a Na & when it comes back in use it's power to drive the G into the blood.

 

[dentaldudecal]

Remember that glucose entering a cell must be used up for energy or stored as glycogen. Sugars are not stored as monomers as it would create too high of osmolarity in the cell causing it to lyse (hypotonic).
Your second question is asking about transporting glucose from the lumen of the small intestines to the blood stream. Remember that glucose is hydrophillic and therefore needs a transporter to cross the intestinal wall. In order to carry this out, secondary active transport is used in which a downhill (-G, spontaneous) reaction is coupled to an uphill (+G, nonspontaneous) reaction.