GLYCOLYSIS QUESTION!!!!!!!!

[deleted621740]

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Alright,

I am incredibly gifted when it comes to overanalyzing incredibly simple questions, and the glycolysis question that I've pasted below has not been an exception. Can someone please offer their insights regarding what is meant by "an immediate/direct connection"? Is there some mathematical or graphical relationship that I have somehow overlooked???

My conclusion is that there is no "direct" connection between intracellular glucose concentration and the glycolytic rate given that the pathway can be regulated at multiple steps and given that flux control can be distributed across multiple enzymes. However, I am tempted to say that there is a direct relationship given that an increase in intracellular glucose obviously results in an increase in substrate for all glycolytic enzymes, and thus an increase in their velocity. Insights??

"Because glucose is polar, it does not diffuse into cells by any appreciable margin. Consider the mechanism/method of glucose import and conclude whether a direct/immediate connection exists between intracellular glucose concentration and glycolysis rate (that is, the quantity of glucose moved through all steps of the glycolytic pathway vs. the amount of glucose in that cell). In other words, does the intracellular glucose concentration directly determine the rate of glycolysis? If there is a link, describe it. If not, expand upon this as well."

Thank You!!!

 

[MarshMedic]

I think your initial conclusion is correct because of negative feedback inhibition of further glycolysis in the presence of adequate ATP.

 

[stgt9202]

hmmm well the question is asking you to look at how glucose is imported into the cell...this means two things, 1) concentration of glucose in the blood and 2) the roles of insulin and glucagon and their roles on activating GLUT4 glucose channels.
I would say that intracellular glucose however does directly affect the rate of glycolysis. Think of it in the point of view of hormones and state of the cell. If you just ate a big meal, your blood glucose levels are going to go up so insulin is released and glucose enters your muscle cells. Now depending on the cells' needs, that intracellular glucose can immediately be used for glycolysis (say your working out now and need to expend energy) by being converted to G6P by hexokinase. However, if the cell is just chilling and not in need of energy that glucose will be stored as glycogen..what does that mean? that means that the concentration of intracellular glucose decreases as you're increasing the concentration of glycogen storage.

You can also discuss the other steps of glycolysis and how NADH and ADP play crucial roles, but I think since the question is asking you to focus on glucose import into the cell I would stick to how insulin and glucagon play roles in creating intracellular levels of glucose.

Hope this helps!

 

[deleted621740]

hmmm well the question is asking you to look at how glucose is imported into the cell...this means two things, 1) concentration of glucose in the blood and 2) the roles of insulin and glucagon and their roles on activating GLUT4 glucose channels.
I would say that intracellular glucose however does directly affect the rate of glycolysis. Think of it in the point of view of hormones and state of the cell. If you just ate a big meal, your blood glucose levels are going to go up so insulin is released and glucose enters your muscle cells. Now depending on the cells' needs, that intracellular glucose can immediately be used for glycolysis (say your working out now and need to expend energy) by being converted to G6P by hexokinase. However, if the cell is just chilling and not in need of energy that glucose will be stored as glycogen..what does that mean? that means that the concentration of intracellular glucose decreases as you're increasing the concentration of glycogen storage.

You can also discuss the other steps of glycolysis and how NADH and ADP play crucial roles, but I think since the question is asking you to focus on glucose import into the cell I would stick to how insulin and glucagon play roles in creating intracellular levels of glucose.

Hope this helps!

Thanks for your input!
In light of your comments--which I completely support and have considered thoroughly--I can see where my confusion is stemming from. We're first asked to consider transport mechanisms and then the question is suddenly reduced to "does the intracellular glucose concentration directly determine the rate of glycolysis". My apprehension to roll with your answer above is that word "directly". There is no question that glucose concentrations influence the rate of glycolysis--but does it wholly determine the rate???

Perhaps I am being over-analytical but I hope that my frustration isn't unwarranted.

 

[UberUdder09]

I think the fact that there is any regulation mechanism (hormones, inhibition, etc.) you can conclude that glucose levels (either present or being transported) are not directly related to the rate of glycolysis. If you attempted to plot glucose vs. glycolysis rate they would not be easily relatable due to a number of factors. I agree with your overanalyzing and the word directly would imply a mathematical relationship such as A = k*B which is obviously not the case.

Good luck!

 

[longhaul3]

The rate-limiting step in glycolysis is the action of PFK and is well downstream of the action of hexokinase. Even G6P does not directly impact the rate of glycolysis, since G6P is also a substrate for glycogen synthesis.

 

[kraskadva]

Alright,

I am incredibly gifted when it comes to overanalyzing incredibly simple questions, and the glycolysis question that I've pasted below has not been an exception. Can someone please offer their insights regarding what is meant by "an immediate/direct connection"? Is there some mathematical or graphical relationship that I have somehow overlooked???

My conclusion is that there is no "direct" connection between intracellular glucose concentration and the glycolytic rate given that the pathway can be regulated at multiple steps and given that flux control can be distributed across multiple enzymes. However, I am tempted to say that there is a direct relationship given that an increase in intracellular glucose obviously results in an increase in substrate for all glycolytic enzymes, and thus an increase in their velocity. Insights??

"Because glucose is polar, it does not diffuse into cells by any appreciable margin. Consider the mechanism/method of glucose import and conclude whether a direct/immediate connection exists between intracellular glucose concentration and glycolysis rate (that is, the quantity of glucose moved through all steps of the glycolytic pathway vs. the amount of glucose in that cell). In other words, does the intracellular glucose concentration directly determine the rate of glycolysis? If there is a link, describe it. If not, expand upon this as well."

Thank You!!!

This is straight up kinetics. Look up the Michaelis-Menton Equation, if you haven't hit that in your lecture already. And refresh on Le Chatlier's principle.
The point of telling you that glucose is polar and does not diffuse in, is to say that the [glucose] in the cell is not affected by the [glucose] outside the cell (without other steps involved anyway).
If the cell is under normal (aerobic) conditions, and is functional, then of course there is a direct connection. Pyruvate is pulled out at the end of glycolysis into the citric acid cycle and other pathways, glucose is pulled in. If glucose is low, then the rate of reaction will decrease, because rate is directly related to substrate concentration (m-m eq.)

-A BioChem TA

 

[WedgeDawg]

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