Question

In which of the following reactions of glycolysis, a molecule of water is removed from the substrate?
A. Glucose → Glucose-6-phosphate
B. Fructose-6-phosphate → Fructose-1,6 bisphosphate
C. 2-phosphoglycerate → Phosphoenolpyruvate
D. Phosphoenolpyruvate → Pyruvate

Answer 1

Hint: Glycolysis is the mechanism by which one glucose molecule is converted into two pyruvate molecules, two hydrogen ions, and two water molecules. This method synthesizes the 'high energy' molecules \[ATP\] and \[NADH\]. The pyruvate molecules then lead to a link reaction in which \[acetyl-coA\] is formed.

Complete answer:
The process of glycolysis occurs in 10 stages which are explained below:
Step 1: A phosphate group is added to glucose through the action of the enzyme hexokinase in the cell cytoplasm. In this, from \[ATP\] a phosphate group is transferred to form \[glucose\] \[6-phosphate\],
Step 2: \[Glucose-6-phosphate\] is isomerized by the enzyme \[phosphoglucomutase\] into \[fructose\text{ }6-phosphate\].
Step 3: The other \[ATP\] molecule passes the phosphate group to \[fructose\text{ }6-phosphate\] and, through the action of the enzyme phosphofructokinase, transforms it into \[fructose\text{ }1,6-bisphosphate\].
Step 4: \[fructose\text{ }1,6-bisphosphate\]is converted by the enzyme aldolase into \[glyceraldehyde\text{ }3-phosphate\] and \[dihydroxyacetone\text{ }phosphate\], which are isomers of each other.
Step 5: Dihydroxyacetone phosphate is converted into \[glyceraldehyde\text{ }3-phosphate\] by triose-phosphate isomerase, which is the substrate in the glycolysis step.
Phase 6: There are two reactions to this step:
The \[glyceraldehyde\text{ }3-phosphate\text{ }dehydrogenase\] enzyme transfers 1 molecule of hydrogen to form \[NAD{{H}^{+}}and\text{ }{{H}^{+}}\]from glyceraldehyde phosphate to nicotinamide adenine dinucleotide.
To form \[1,3-bisphosphoglycerate,\text{ }glyceraldehyde\text{ }3-phosphate\text{ }dehydrogenase\] adds phosphate to the oxidized glyceraldehyde phosphate.
Step 7: With the aid of phosphoglycerokinase, phosphate is transferred from \[1,3-bisphosphoglycerate\] to ADP to form \[ATP\]. Two \[phosphoglycerate\] and \[ATP\]molecules are thus obtained at the end of this reaction.
Step 8: From the third to the second carbon, the phosphate of both \[phosphoglycerate\] molecules is transferred to create two 2- \[phosphoglycerate\] molecules by the phosphoglyceromutase enzyme.
Step 9: To form phosphoenolpyruvate, the enzyme enolase extracts a water molecule from 2- \[phosphoglycerate\].
Step 10: By the action of pyruvate kinase, a phosphate from phosphoenolpyruvate is transferred to ADP to form pyruvate and \[ATP\]. Two pyruvate ions and \[ATP\] are the end products.
Options A and B reflect the addition, respectively, of the phosphate group to glucose and fructose 6 phosphates.
A water molecule is eliminated during the formation of Phosphoenolpyruvate (PEP) from 2-phosphoglycerate. The enzyme enolase catalyzes this reaction. This is the glycolysis stage. This reaction in the cytoplasm occurs. Reversible removal of a molecule of water from \[2-phosphoglycerate\] requires dehydration of \[2-phosphoglycerate\] to \[phosphoenolpyruvate\].
Option D illustrates phosphoenolpyruvate dephosphorylation into pyruvate.

So, choice C-2-phosphoglycerate → Phosphoenolpyruvate is the correct answer.

Note: Humans use \[NADH\] supplements as medicines. \[NADH\] is used to enhance mental clarity, alertness, focus, and memory, as well as to treat Alzheimer's disease and dementia. Due to its role in energy production, \[NADH\] is also used to improve athletic performance and treat chronic fatigue syndrome (CFS).