Introduction to Carbohydrate Metabolism - Glycolysis

Question 0

In glycolysis, what are the starting substrate and possible ending products?

Answer 0

Starting substrate: Glucose

Possible ending products: pyruvate or lactate

Question 1

Where in the cell does glycolysis take place?

Answer 1

In the cytosol

Question 2

What must every cell that metabolizes glucose do first? What enzymes do this?

Answer 2

Every cell must phosphorylate glucose.

The enzyme that does phosphorylates glucose is hexokinase (3 types found in all tissues) or glucokinase (only in liver).

Hexokinase is inhibited by G-6-P, while Glucokinase is not.

Question 3

In glycolysis, what is the enzyme, substrate, and product for the commited step reaction? Is ATP generated or used in this reaction?

Answer 3

In the COMMITTED step:

Enzyme: Phosphofructokinase-I
Substrate: Fructose-6-phosphate
Product: fructose-1,6-bisphosphate

ATP is not made in this step, but used to add a phosphate group to fructose-6-phosphate

Question 4

What are some control factors which affect glycolysis?

Answer 4

1) G-6-P inhibits Hexokinases from phosphorylating glucose

2) The major control factors are in the COMMITTED Step, where fructose-6-phosphate is converted to fructose-1,6-bisphosphate.
- In muscle, glycolysis must be able to provide ATP under anaerobic conditions, the main negative allosteric effects are ATP and citrate (causes dimerization of PFK-I). AMP, AD, cAMP, and P_i reduces the effects of ATP.
- In liver the rate of flux through this pathway is controlled to either maintain blood glucose levels or provide metabolic intermediates the most important activator is fructose-2,6-bisphosphate. This effector concentration is controlled by its synthesis being inhibited by high serum levels of glucagon and stimulated by vasopressin and phenylephrine. Fructose-2,6-BP also inhibits F-1,6-BPase, which converts fructose-1,6-bisphosphate to Fructose-6-phosphate, allowing the reaction to move forward.

3) Fluoride is a potent inhibitor of the conversion of 2-phosphoglycerate to phosphoenolpyruvate because it forms a magnesium fluoro phosphate at the active site, causing accumulation of phosphoglycerates.

Question 5

In what steps is ATP generated?

Answer 5

ATP is generated in:

Step 7: Conversion of 1,3-Bisphosphoglycerate to 3-Phosphoglycerate by phosphoglycerate kinase (very powerful driving force step)

Step 10: Conversion of Phosphoenolpyruvate (PEP) and water with Mg2+, K+ to Pyruvate by Pyruvate Kinase

Question 7

True or False: Fructose-2,6-Bisphosphate is positive allosteric inhibitor of PFK-I.

Answer 7

True

Question 8

What step in glycolysis produces NADH?

Answer 8

glyceraldehyde 3-phosphate –> 1,3-bisphosphoglycerate (via glyceraldehyde phosphate dehydrogenase)