EXSC 223 Chapter 24 The 2 Fates of Pyruvate

Overview of Glycolysis and Pyruvate Fate

• Focuses on the fate of pyruvate molecules produced at the end of glycolysis.

• The fate of NADPH is important and linked to pyruvate's fate.

Glycolysis Recap

Substrate Requirement

• Glycolysis begins with glucose, a water-soluble molecule absorbed from the diet.

• Glucose requires the GLUT transporter protein to cross cell membranes due to its solubility.

Phosphorylation of Glucose

• Enzyme hexokinase phosphorylates glucose on carbon 6 using ATP, trapping it inside the cell.

• Phosphofructokinase (PFK) phosphorylates glucose again on carbon 1, marking the investment phase.

Cleavage Phase

• The six-carbon glucose is split into two three-carbon molecules (glyceraldehyde-3-phosphate).

• Only one molecule is G3P, and the other must convert to G3P to yield energy.

Energy Yield from Glycolysis

• Result: Two G3P molecules can be processed to extract energy.

• During the investment return phase:

  • Produce two NADPH molecules

  • Produce four ATP molecules

• Key Points:

  • Total ATP produced = 4

  • Net ATP gain = 2 (after two invested)

Fate of Pyruvate

Two Possible Pathways

• Aerobic: Involves cellular respiration within mitochondria.

• Anaerobic: Metabolites produced without oxygen involvement.

Anaerobic Pathway

• Anaerobic metabolism occurs regardless of oxygen presence; often produces lactate.

• Produced via lactate dehydrogenase (LDH) by converting pyruvate and burns NADPH.

• Lactate allows continued ATP production by recycling NAD needed for glycolysis.

Importance of Lactate Production

• Vital for maintaining ATP production to prevent cell death.

• Creates a NAD recycling program enabling ongoing glycolysis.

Aerobic Pathway

Mitochondrial Function

• Mitochondria present two membranes and have their own DNA.

• Process refers to pyruvate transport into the mitochondria and conversion to acetyl-CoA.

Conversion Process

• Pyruvate dehydrogenase enzyme crosses the membrane.

• Removes one carbon (producing CO2) and transfers hydrogens and electrons onto NAD (producing NADH).

• Coenzyme A is added to form acetyl-CoA.

Importance of Acetyl-CoA

• Acetyl-CoA is a crucial intermediate for the citric acid cycle.

• In short, pyruvate fate is important for energy production and metabolic pathways.