[MissDee]

Questions:

1. How do high glucose levels affect the rate of glycolysis? Which enzymes will be affected, and will the rate increase or decrease?

2. How do high ATP levels affect the rate of glycolysis? Which enzymes will be affected, and will the rate increase or decrease?

3. How do high NADH levels affect the rate of glycolysis? Which enzymes will be affected, and will the rate increase or decrease?


** I think for all of them the rates will increase. However, I'm not sure which enzymes are involved. Can someone please double-check the answers?? **


Answers:

1. The enzyme hexokinase phosphorylates (adds a phosphate group to) glucose in the cell's cytoplasm. In the process, a phosphate group from ATP is transferred to glucose producing glucose 6-phosphate.

Glucose (C6H12O6) + hexokinase + ATP → ADP + Glucose 6-phosphate (C6H11O6P1)

The enzyme phosphoglucoisomerase converts glucose 6-phosphate into its isomer fructose 6-phosphate. Isomers have the same molecular formula, but the atoms of each molecule are arranged differently.

Glucose 6-phosphate (C6H11O6P1) + Phosphoglucoisomerase → Fructose 6-phosphate (C6H11O6P1)



2. The enzyme phosphofructokinase uses another ATP molecule to transfer a phosphate group to fructose 6-phosphate to form fructose 1, 6-diphosphate.

Fructose 6-phosphate (C6H11O6P1) + phosphofructokinase + ATP → ADP + Fructose 1, 6-diphosphate (C6H10O6P2)



3. The enzyme triose phosphate dehydrogenase serves two functions in this step. First the enzyme transfers a hydrogen (H-) from glyceraldehyde phosphate to the oxidizing agent nicotinamide adenine dinucleotide (NAD+) to form NADH. Next triose phosphate dehydrogenase adds a phosphate (P) from the cytosol to the oxidized glyceraldehyde phosphate to form 1, 3-diphoshoglyceric acid.

A. Triose phosphate dehydrogenase + 2 H- + 2 NAD+ → 2 NADH + 2 H+

B. Triose phosphate dehydrogenase + 2 P + 2 glyceraldehyde phosphate (C3H5O3P1) → 2 molecules of 1,3-diphoshoglyceric acid (C3H4O4P2)

[Matias Ekstrand]

What is the goal of glycolysis? What happens if we add more of the products? Will that make it go faster?

[MissDee]

What is the goal of glycolysis? What happens if we add more of the products? Will that make it go faster?

Glycolysis' purpose is to break down glucose down to form two pyruvates.

High ATP levels inhibit phosphofructokinase. High ATP levels also enable ATP to bind to allosteric site, causing a conformation change and shutting down the enzyme. It also slows down the conversion of pyruvate to Acetyl CoA by phosporylating the pyruvate dehydrogenase enzyme by changing its shape and shutting it down. With all of this considered, does this mean that high ATP levels slow glycolysis down?

High NADH levels inhibit pyruvate dehydrogenase.

For high glucose levels, this will increase the rate of glycolysis, since it wants to break down glucose to form two pyruvates. Correct?

Please help me out here.

[Matias Ekstrand]

What is the goal of glycolysis? What happens if we add more of the products? Will that make it go faster?

Glycolysis' purpose is to break down glucose down to form two pyruvates.

It's also part of a bigger system to generate energy for the cell. If we have lots of energy (ATP), glycolysis is not needed.

High ATP levels inhibit phosphofructokinase. High ATP levels also enable ATP to bind to allosteric site, causing a conformation change and shutting down the enzyme. It also slows down the conversion of pyruvate to Acetyl CoA by phosporylating the pyruvate dehydrogenase enzyme by changing its shape and shutting it down. With all of this considered, does this mean that high ATP levels slow glycolysis down?

Pyruvate dehydrogenase is an enzyme which is not part of the glycolysis (we have already created pyruvate, right?). Your first enzyme is correct, but there is another one you have not yet mentioned. Look at the enzymes that use ATP or ADP to find the second one. The effect of high levels of ATP is to slow down glycolysis.

High NADH levels inhibit pyruvate dehydrogenase.

Once again, this is not part of glycolysis. Look at another enzyme that creates NADH in the glycolysis.

For high glucose levels, this will increase the rate of glycolysis, since it wants to break down glucose to form two pyruvates. Correct?

I'm not sure about that. Glycolysis is mainly regulated by the cell's need of energy and not the amount of available glucose. The enzymes (hexokinase) already active may have an easier time finding glucose, but then again this will mean an increase of G6P which very effectively inhibit hexokinase. The only real way to stimulate more breakdown of glucose in glycolysis is by making G6P go away through stimulating all the other enzymes to process it.