Glycolysis Overview

Study Notes

Overview of Glycolysis

Glucose serves as a central metabolite, rich in potential energy, with a standard free-energy change of -2,840 kJ/mol upon complete oxidation.
Can be stored as polymers like starch or glycogen, maintaining low cytosolic osmolarity.
Acts as a versatile precursor for various biosynthetic reactions.

Glycolysis Pathway

First metabolic pathway elucidated; derives from Greek words meaning "sweet" and "splitting."
An essential pathway for glucose catabolism with the largest carbon flux in cells.
Breaks down one glucose molecule into two pyruvate molecules through a series of enzyme-catalyzed reactions.
Key energy source in certain mammalian tissues (e.g., erythrocytes, renal medulla, brain, sperm).
Produces energy carriers ATP and NADH during the process.

Steps of Glycolysis

Comprises 10 steps, with the first 5 forming the preparatory phase.
In the preparatory phase, ATP is invested to increase the free-energy content of intermediates, leaving glyceraldehyde 3-phosphate as a common product.

Phosphorylation and Retention

Phosphorylated sugars typically cannot exit the cell due to lack of transporters on plasma membrane.
Initial phosphorylation allows retention of intermediates without further energy input, despite significant concentration differences.
Energy from phosphoanhydride bond breakage (e.g., ATP) is conserved in the formation of phosphate esters like glucose 6-phosphate.

Key Reactions

Conversion of Glucose 6-Phosphate to Fructose 6-Phosphate: Occurs before the committed step of glycolysis.
Phosphorylation of Fructose 6-Phosphate: The PFK-1 reaction is largely irreversible and commits fructose 6-phosphate to the glycolytic pathway.
Cleavage of Fructose 1,6-Bisphosphate: Involves reversible aldol condensation; despite a positive standard free-energy change, the reaction is reversible due to reactants' low concentrations in cells.

Interconversion of Triose Phosphates

Two triose phosphates produced (glyceraldehyde 3-phosphate and dihydroxyacetone phosphate); only glyceraldehyde 3-phosphate is directly degraded in glycolysis.
Dihydroxyacetone phosphate quickly converts to glyceraldehyde 3-phosphate.

Energy Gain in Glycolysis

Energy payoff occurs in later steps where glyceraldehyde 3-phosphate is oxidized and phosphorylated to form 1,3-bisphosphoglycerate.
Two molecules of pyruvate are formed while conserving energy via the phosphorylation of ADP to ATP, resulting in a net yield of two ATP per glucose.
Additionally, two NADH electron carriers are produced.

Oxidation of Glyceraldehyde 3-Phosphate

First key energy-conserving reaction leading to ATP formation.
The oxidation of the aldehyde group of glyceraldehyde 3-phosphate results in a carboxylic acid anhydride with phosphoric acid.

Description

This quiz explores glycolysis, a crucial metabolic pathway in cellular respiration. It covers the importance of glucose in energy production and its storage forms like starch and glycogen. Test your knowledge on how glucose functions as a versatile precursor in metabolism.