EMP Pathway: Glycolysis Stage I

• Carbohydrate catabolism involves breaking down carbohydrates to release energy.

Embden-Meyerhof-Parnas (EMP) Pathway: Glycolysis Stage I

• The Embden-Meyerhof-Parnas (EMP) pathway is also known as glycolysis.
• In glycolysis stage I, glucose is converted into two molecules of glyceraldehyde 3-phosphate (GAP).
• The net balance for this stage is: Glucose + 2 ATP → 2 GAP + 2 ADP.
• Specific enzymes facilitate each step of the glycolysis I.
• Glucose is converted to glucose-6-phosphate using ATP with the help of PTS/Glucokinase.
• Glucose-6-phosphate is isomerized to fructose-6-phosphate.
• Fructose-6-phosphate is converted to fructose-1,6-bisphosphate using ATP via phosphofructokinase.
• Fructose-1,6-bisphosphate is split into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate (GAP) by fructose-bisphosphate aldolase.
• Dihydroxyacetone phosphate is then converted to glyceraldehyde 3-phosphate (GAP) by triose phosphate isomerase.

Entner-Doudoroff (ED) Pathway: Glycolysis Stage I

• In the Entner-Doudoroff (ED) pathway, glucose is converted into glyceraldehyde 3-phosphate (GAP) and pyruvate.
• The net balance for this pathway: Glucose + ATP + NAD(P)+ → GAP + pyruvate + NAD(P)H + ADP.
• Specific enzymes facilitate each step of the ED pathway.
• After glucose conversion into glucose-6-phosphate using ATP and PTS/Glucokinase, glucose-6-phosphate is dehydrogenated to 6-phosphogluconolactone, producing NAD(P)H.
• 6-phosphogluconolactone is converted to 6-phosphogluconate via 6-phosphogluconolactonase.
• 6-phosphogluconate is dehydrated to 2-keto-3-deoxy-6-phosphogluconate.
• 2-keto-3-deoxy-6-phosphogluconate is then split into glyceraldehyde 3-phosphate (GAP) and pyruvate.

Pentose Phosphate Pathway (PPP)

• The pentose phosphate pathway (PPP) has an oxidative branch, where glucose is converted into glyceraldehyde 3-phosphate (GAP).
• The net balance: Glucose + 6NAD(P)+ ATP = GAP + 3 CO2 + 6 NAD(P)H +ADP.
• Specific enzymes catalyze each step in the PPP.
• Glucose is converted to glucose-6-phosphate using ATP.
• Glucose-6-phosphate is then dehydrogenated to 6-phosphogluconolactone to produce NAD(P)H.
• 6-phosphogluconolactone is converted to 6-phosphogluconate.
• 6-phosphogluconate is dehydrogenated and decarboxylated to ribulose 5-phosphate and produce NAD(P)H and CO2.
• Ribulose 5-phosphate is converted to ribose 5-phosphate.
• The rearrangement phase involves interconversion of sugars.
• Fructose-6-phosphate and glyceraldehyde 3-phosphate (GAP) are produced from erythrose-4-P, sedoheptulose -7P, ribose-5-P and xylulose 5-P.

Glycolysis Stage II: Glyceraldehyde-3-phosphate (GAP) Conversion

• During glycolysis stage II, glyceraldehyde-3-phosphate (GAP) is converted to pyruvate.
• The net balance: GAP → pyruvate + 2ATP + NADH.
• GAP is oxidized and phosphorylated to 1,3-bisphosphoglycerate with the help of glyceraldehyde 3-phosphate dehydrogenase.
• 1,3-bisphosphoglycerate transfers a phosphate group to ADP, forming ATP and 3-phosphoglycerate with the help of phosphoglycerate kinase.
• 3-phosphoglycerate is converted to 2-phosphoglycerate by phosphoglycerate mutase.
• 2-phosphoglycerate is dehydrated to phosphoenolpyruvate (PEP) by enolase.
• PEP transfers a phosphate group to ADP, forming ATP and pyruvate with the help of pyruvate kinase.

Krebs Cycle (Tricarboxylic Acid (TCA) Cycle)

• Pyruvate is oxidized in the Krebs cycle.
• The net balance: pyruvate + 4 NAD+ + FAD+ + ADP -> 3CO2 + 4 NADH/H+ + FADH2 + ATP.
• Pyruvate is converted to acetyl-CoA, releasing CO2 and producing NADH.
• Acetyl-CoA enters the cycle by combining with oxaloacetate to form citrate.
• Citrate undergoes a series of reactions, releasing 2 molecules of CO2, 3 molecules of NADH, and 1 molecule of FADH2, regenerating oxaloacetate to continue the cycle.
• ATP is also produced during the conversion of succinyl-CoA to succinate.