Question

Which steps in the glycolysis pathway are irreversible?

Answer 1

Glycolysis is a process through which glucose molecules are converted into pyruvic acid molecules. In the glycolysis process one molecule glucose is converted into two molecules of pyruvic acids. The free energy that is released in the glycolysis process is used to form the high-energy molecules ATP and reduced nicotinamide adenine dinucleotide. Glycolysis is a chain of reactions catalysed by enzymes.

Complete answer:
There are ten steps in the glycolysis pathway. Out of these ten reactions seven are reversible and three are irreversible.

The irreversible steps of glycolysis are the conversions from glucose into glucose $6$ phosphate, fructose into $1,6$ bisphosphate and from phosphoenolpyruvate into pyruvic acid.

Step $1$- The first step of the glycolysis is the phosphorylation of fructose to fructose $1 -$phosphate. Here the catalyst is Fructokinase. Fructose $1 -$phosphate is then split into glyceraldehyde and dihydroxyacetone phosphate in further steps of glycolysis.

Step $3$ - Phosphorylation of fructose$- 6 -$phosphate is the third step of glycolysis. Here the catalyst enzyme phosphofructokinase. A second Adenosine triphosphate molecule donates a high-energy phosphate to fructose$- 6 -$phosphate. It produces fructose$- 1,6 -$bisphosphate.

Step $10$- This is the last step of glycolysis. This step of glycolysis converts phosphoenolpyruvate into pyruvate. Here the catalyst is pyruvate kinase enzyme. This last reaction is the transfer of a phosphate group.

Note:
Glycolysis is a metabolic pathway or process that does not need oxygen. The extensive occurrence of glycolysis in other species specify that it is an ancient metabolic pathway.
In fact, the reactions that trump up the glycolysis process and its parallel pathway. The pentose phosphate process occurs in the conditions that don't need oxygen of the Archean oceans, also catalysed by metal in the absence of enzymes.