Glycolysis Main Steps Quiz

Glycolysis is a fundamental metabolic process that occurs in all living organisms. It's the breakdown of glucose into pyruvate, which generates energy through ATP production. Glycolysis takes place in the cytoplasm of cells and involves ten key stages with three major regulatory points. Here are the main steps of glycolysis:

1. Glucose enters the cell: Glucose passes through the plasma membrane and enters the cytosol via facilitated diffusion or active transport mechanisms.

2. Phosphorylation: The six-carbon sugar glucose is converted into a phosphate ester by a kinase enzyme. This step requires one molecule of ATP, which acts as a high-energy donor, creating glucose 6-phosphate (G6P).

3. Isomerization: An aldolase enzyme catalyzes the cleavage of the hemiacetal bond between carbon 1 and carbon 2, forming two three-carbon sugars called trioses — dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P). DHAP immediately undergoes isomerization to form another G3P molecule, ensuring equal amounts of both intermediates.

4. Phosphorylation again: Each G3P molecule is phosphorylated by another ATP molecule. Two new high-energy compounds are created: 1,3-bisphosphoglycerate (1,3BPG) from DHAP and 3-phosphoglycerate (3PG) from G3P.

5. Triose Phosphate Isomerization: Both 1,3BPG and 3PG go through another isomerization reaction, converting them back into G3P and DHAP, respectively. By this point, half of the glucose has been broken down into smaller units.

6. More phosphorylation!: The remaining G3Ps each accept another phosphate group from ATP, producing 1,3-bisphosphoglycerate (1,3BPG) and 3-phosphoglycerate (3PG).

7. Two more isomerizations: As before, the reaction continues through yet another round of isomerization and phosphorylation.

8. Formation of 1,3-Bisphosphoglycerate Mutase: Two 1,3BPG molecules combine to form a single compound, 3-phosphoglycerate (3PG), through a nucleophilic attack and a dehydration process.

9. Enolization: The 3PG goes through an enolization reaction, giving rise to another intermediate—2-phosphoglycerate (2PG).

10. The end product: Finally, a kinase enzyme adds another phosphate group to 2PG, yielding the end product—a three-carbon molecule called 3-phosphoglycerate (3PG).

At this stage, the ten steps have completed the conversion of a six-carbon glucose molecule into two three-carbon 3PG molecules. However, due to the reversibility of some reactions earlier in the pathway, the net result is only one molecule of 3PG in the forward direction and one molecule of G3P in the reverse direction. These 3PG molecules can continue undergoing further processes, leading to the formation of ATP and the regeneration of G6P through the reactions of glycolysis.

In summary, glycolysis is a complex process involving multiple reactions that convert glucose into pyruvate, generating energy through the creation of ATP while also providing precursors for other biosynthetic pathways. Understanding these ten key steps helps us appreciate how our cells extract energy from nutrients like glucose to fuel their activities.