Glycolysis 🧪

Glycolysis is the first stage of aerobic respiration. It occurs in the cytoplasm.

The name "glycolysis" literally means the breakdown of glucose:

Starting with Glucose

Glycolysis begins with a glucose molecule (C6H12O6C6​H12​O6​), which is a six-carbon molecule.

Step 1: Hexose Bisphosphate Formation

In the first step, glucose receives two phosphate groups donated by two ATP molecules, transforming into hexose bisphosphate.

• Two ATP molecules are converted to two ADP molecules.

• "Hex" refers to six (carbons), and "ose" refers to sugar.

• "Bis" refers to the presence of two phosphate groups.

Step 2: Splitting into Triose Phosphate

Hexose bisphosphate splits into two triose phosphate molecules. This occurs by cutting the hexose bisphosphate right down the middle.

Step 3: Triose Bisphosphate Formation

A phosphate group from the cytoplasm is added to each triose phosphate, creating triose bisphosphate. It's important to note:

• The phosphate group does not come from ATP.

• It's an inorganic phosphate group already present in the cytoplasm.

Step 4: Conversion to Pyruvate

Triose bisphosphate is converted into pyruvate.

• Two ADP molecules collect the two phosphate groups, becoming two ATP molecules.

• A coenzyme called NAD steals a hydrogen atom from triose bisphosphate, becoming reduced NAD.

Summary of Glycolysis

1. Glucose is converted into hexose bisphosphate with the help of two ATP molecules.

2. Hexose bisphosphate breaks down into two triose phosphate molecules.

3. An inorganic phosphate group is added to each triose phosphate, forming triose bisphosphate.

4. Triose bisphosphate undergoes reactions:

   • Two ADP molecules steal two phosphate groups to become two ATP molecules.

   • NAD steals a hydrogen atom, becoming reduced NAD.

5. The final product is two pyruvate molecules, which are then transported into the mitochondria for aerobic respiration.

Phosphorylation Types

Products and Their Fate 🎯

Each reduced NAD molecule can produce a maximum of three ATP molecules in oxidative phosphorylation. This is why producing reduced NAD is crucial.