Glycolysis (Glyco=Glucose; lysis= splitting) is the oxidation of glucose (C 6) to 2 pyruvate (3 C) with the formation of ATP and NADH.
- It is also called as the Embden-Meyerhof Pathway
- Glycolysis is a universal pathway; present in all organisms:
- from yeast to mammals.
- It is a universal anaerobic process where oxygen is not required
- First phase of cellular reparation in aerobic organisms
- It occurs in the cytosol of cell cytoplasm in both eukaryotes and prokaryotes
In the presence of O2, pyruvate is further
oxidized to CO2.
In the absence of O2, pyruvate can be fermented to lactate or ethanol.
Glucose + 2NAD+ + 2 Pi + 2 ADP = 2 pyruvate + 2 ATP + 2NADH + 2 H2O
Here is the video that explains 10 Steps of Glycolysis
2 stages of Glycolysis
First phase: Preparatory Phase or investment phase Phosphorylation of Glucose and its conversion to Glyceraldehyde 3-phosphate. 2 ATP used in this pahse
Second phase: Payoff phase
Oxidative conversion of Glyceraldehyde 3-phosphate to pyruvic acid
(4 ATP and 2 NADH produced)
10 Steps of GlycolysisReaction 1: Phosphorylation of glucose to glucose-6 phosphate
This reaction requires energy and so it is coupled to the hydrolysis of ATP to ADP and Pi.
Enzyme: hexokinase (regulatory step). It has a low Km for glucose; hexokinase phosphorylates glucose that enters the cell
Irreversible step. So the phosphorylated glucose gets trapped inside thecell. Glucose transporters transport only free glucose
Reaction 2: Isomerization of glucose-6-phosphate to fructose 6-phosphate. The aldose sugar is converted into the keto isoform.
This is a reversible reaction. The fructose-6-phosphate is quickly consumed and the forward reaction is favored.
Reaction 3: is another kinase reaction. Phosphorylation of the hydroxyl
group on C1 forming fructose-1,6- bisphosphate.
Enzyme: phosphofructokinase. This allosteric enzyme regulates the pace of glycolysis (rate limiting step).
ATP is used
Second irreversible reaction of the glycolytic pathway.
Reaction 5: DHAP and GAP are isomers and can readily inter-convert by the
enzyme triose-phosphate isomerase.
Reaction 4: fructose-1,6-bisphosphate splits into 2 3-carbon molecules, one aldehyde and one ketone: dihyroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP).
The enzyme is aldolase.
GAP is a substrate for the next step in glycolysis so all of the DHAP is converted to GAP. So, 2 molecules of GAP are formed from each molecule of glucose
Up to this step 2 ATP is used
Second phase: Payoff phase
2 GAP molecules generated from each glucose, therefore each of the remaining reactions occur twice for each glucose molecule being oxidized.
Reaction 6: GAP is dehydrogenated by the enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH). In the process, NAD+ is reduced to NADH + H+ from NAD. Oxidation is coupled to the phosphorylation of the C1
1,3-bisphosphoglycerate is formed
Reaction 7: This high energy bond of BPG at C-1 is hydrolyzed to a carboxylic acid and the energy released is used to generate ATP from ADP.
Reaction 8: The phosphate group shifts from C3 to C2 to form 2-phosphoglycerate.
Reaction 9: Dehydration reaction catalyzed by enolase (a lyase). A water molecule is removed to form phosphoenolpyruvate which has a double bond between C2 and C3.
Reaction 10: Enolphosphate is a high energy bond. It is hydrolyzed to form the enolic form of pyruvate with the synthesis of ATP. Irreversible step
Enzyme: pyruvate kinase (regulatory enzyme)
Enol pyruvate quickly changes to a more stable keto pyruvate.
Try this Multiple choice on Glycolysis