Glycolysis Pathway: Pathway, Steps & Products

What Is Glycolysis?

Glycolysis is a metabolic pathway that converts glucose, a six-carbon sugar molecule, into two molecules of pyruvate, each containing three carbons. The process takes place in the cytoplasm of the cell and leads to the formation of ATP and NADH.

Glycolysis is the first stage in cellular respiration and is very crucial for both aerobic and anaerobic production of energy. It is a rapid means to acquire ATP without entering the oxygen-dependent processes; this feature is especially important for the activity of muscles during high-intensity exercises and in anaerobic organisms.

Where Within The Cell Glycolysis Occurs?

• It occurs in the cytosol of prokaryotic cells and the cytoplasm of eukaryotic cells.

• Glycolysis is present in almost all the simple types of cells, like bacteria, to the most complex types, like human cells.

Role Of Glycolysis In Cellular Respiration

• The process of glycolysis initiates the digestion process of the glucose for obtaining energy.

• Pyruvate formed feeds into the Krebs cycle as well as the electron transport chain for further energy extraction inside the mitochondria.

• Glycolysis also directly yields ATP using substrate-level phosphorylation.

• It gives rise to intermediates for other kinds of metabolic pathways and leads to synthesising amino acids and fatty acids as well.

Steps In Glycolysis

Breakdown of the Steps

Step 1

• Glucose phosphorylation by hexokinase/glucokinase:

• Glucose is phosphorylated to glucose-6-phosphate with the use of ATP.

Step 2

• Isomerisation (Phosphoglucose Isomerase)

• Glucose-6-phosphate produced is changed into fructose-6-phosphate.

Step 3

• Second phosphorylation (Phosphofructokinase-1)

• Fructose-6-phosphate is phosphorylated to fructose-1,6-bisphosphate with the usage of another ATP.

Step 4

• Fructose-1,6-bisphosphate Cleavage (Aldolase)

• Fructose-1,6-bisphosphate is cleaved into two three-carbon molecules.

Step 5

• Isomerisation of DHAP to G3P (Triose Phosphate Isomerase)

• DHAP is converted to G3P, resulting in two molecules of G3P.

Step 6

• Oxidation and phosphorylation (Glyceraldehyde-3-Phosphate Dehydrogenase)

• G3P is oxidised, producing NADH, and phosphorylated to 1,3-bisphosphoglycerate.

Step 7

• ATP generation for the first time (Phosphoglycerate Kinase)

• 1,3-bisphosphoglycerate does a phosphate add to the ADP to create that ATP, with a by-product of 3-phosphoglycerate.

Step 8

• Phosphate is shifted (Phosphoglycerate Mutase)

• 3-phosphoglycerate is converted to 2-phosphoglycerate.

Step 9

• Dehydration (Enolase)

• 2-phosphoglycerate dehydrated to phosphoenolpyruvate (PEP).

Step 10

• Second ATP generation (Pyruvate Kinase)

• PEP donates a phosphate group to ADP, to form ATP and pyruvate.

Outputs Of Glycolysis

Glycolysis products

Pyruvate

• Two molecules of pyruvate per glucose molecule.

ATP products

• Net gain of 2 ATP molecules per glucose molecule, this is because whereby 4 is produced, 2 is consumed.

NADH products

• Two molecules of NADH per glucose molecule.

Regulation In Glycolysis

Key regulatory enzymes:

Hexokinase

• The commit regulatory enzyme: inhibited by ATP and citrate; activated by AMP.

Pyruvate Kinase

• Catalyses the final step, is inhibited by ATP and alanine, and activated by fructose-1,6-bisphosphate.

Allosteric Regulation

• Enzymes change shape and activity in response to the binding of regulatory molecules

Feedback Inhibition

• Inhibition of the end products in early steps to prevent over-accumulation of intermediates and unnecessary use of resources.

Recommended Video On 'Glycolysis'