🦠 Where Does Glycolysis Take Place In The Cell?

Glycolysis takes in place in the cytoplasm of the eukaryotic cells.

Question: Where does glycolysis occur in the cell?

a) The cell membrane
b) The Nucleus
c) The cytoplasm ✔️
d) The mitochondria

Answer: The cytoplasm

What is glycolysis and where does it take place?

Glycolysis is a metabolic pathway in which glucose breaks down into pyruvate (three-carbon compound) and released energy.

In both eukaryotic and prokaryotic cells, glycolysis occurs in the cytoplasm. The cytoplasm is a thick fluid consist of water, salts, and proteins and enclosed by the cell membrane.

Glycolysis is a cytoplasmic pathway that occurs in a sequence of 10 steps that are independent of oxygen. This process of extracting energy from glucose is found almost in all living organisms.

How glycolysis occurs?

Glycolysis can be divided in two phases: energy requiring phase and energy releasing phase.

Energy Requiring Phase

In the energy requiring phase, two molecules of ATP gets consumed in the phosphorylation of glucose.

Step 1: In the first step, the glucose gets converted into glucose-6-phosphate with the help of enzyme catalyst hexokinase and ATP molecule as the source of the phosphate.
Step 2: This glucose-6-phosphate gets converted to one of its isomer called fructose-6-phosphate with the help of enzyme catalyst isomerase.
Step 3: The second molecule of ATP is used in step 3 of glycolysis to produce fructose-1,6-bisphosphate from fructose-6-phosphate using the enzyme catalyst phosphofructokinase.
Step 4: In this step, the fructose-1,6-bisphosphate gets destabilized and breaks down into two isomers (three-carbon compound): dihydroxyacetone-phosphate and glyceraldehyde-3-phosphate.
Step 5: In the fifth step, again isomerase enzyme catalyst is used to convert dihydroxyacetone-phosphate into its isomer glyceraldehyde-3-phosphate so that two molecules of single isomers are formed.

Energy Releasing Phase

In this energy-releasing phase, the three-carbon isomer glyceraldehyde-3-phosphate gets converted to pyruvate along with the formation of four ATP and two NADH molecules.

Step 6: In this step, two half-reactions take place simultaneously
- 1. the compound formed in the first phase of glycolysis that is glyceraldehyde-3-phosphate gets oxidized
- 2. And the NAD+ gets reduced to produce NADH. This NADH molecule must be oxidized again to NAD+ otherwise this step will slow down or even stop.
After the oxidization, the glyceraldehyde-3-phosphate compound is phosphorylated to form 1,3-bisphosphoglycerate.
Step 7: 1,3-bisphosphoglycerate donates a phosphate to ADP to form ATP and gets oxidized from the carbonyl group to the carboxyl group with the help of the enzyme catalyst phosphoglycerate kinase to form 3-phosphoglycerate.
Step 8: With the help of enzyme catalyst phosphoglycerate mutase, 3-phosphoglycerate gets converted to one of its isomer 2-phosphoglycerate.
Step 9: In this step dehydration of 2-phosphoglycerate occurs. It loses its water to become phosphoenolpyruvate with the help of catalyst enolase.
Step 10: In this last step, phosphoenolpyruvate loses its phosphate to ADP and gets converted to pyruvate. As ADP accepts the phosphate, the second molecule of ATP gets formed.

This second phase occurs twice to produce two molecules of pyruvate, four molecules of ATP, and two molecules of NADH.