lec 13-Glucose Metabolism: Glycolysis and Anaerobic Metabolism

Vocabulary and key concepts regarding glucose structures, the ten reactions of glycolysis, ATP yields, regulation, and anaerobic metabolism.

Glucose

A monosaccharide immediate energy source that is osmotically active and exists at approximately $10\,g$ in plasma.

Glycogen

A polysaccharide medium-term fuel source with low osmolarity stored at approximately $400\,g$ in tissue stores.

Glycolysis

A metabolic pathway occurring in the cytosol of all tissues that converts one $C_6$ glucose molecule into two $C_3$ pyruvate molecules.

Hexokinase

An enzyme found in all tissues except the liver that traps glucose by phosphorylation; it has a lower $K_m$ and $V_{max}$ and is inhibited by glucose-6-phosphate.

Glucokinase

A liver-specific enzyme that phosphorylates glucose with a higher $K_m$ and $V_{max}$ and is not inhibited by glucose-6-phosphate.

Phosphofructokinase (PFK)

A key regulatory enzyme in glycolysis that catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate using ATP.

Aldolase

The enzyme responsible for splitting the 6-carbon sugar fructose 1,6-bisphosphate into two 3-carbon units: glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.

Glyceraldehyde-3-phosphate dehydrogenase

The enzyme for the oxidation step (Reaction 6) that produces $NADH + H^+$ while converting glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate.

Substrate level phosphorylation

A method of ATP synthesis where a phosphate group is transferred directly from a substrate to ADP, occurring in Reactions 7 and 10 of glycolysis.

Phosphoglycerate kinase

The enzyme that produces the first 2 molecules of ATP in glycolysis by converting 1,3-bisphosphoglycerate to 3-phosphoglycerate.

Phosphoenolpyruvate (PEP)

A high-energy intermediate produced by enolase in Reaction 9 that is used to generate ATP in the final step of glycolysis.

Pyruvate kinase

The enzyme catalyzing the final irreversible step of glycolysis, converting PEP to pyruvate and producing ATP.

Anaerobic Glycolysis

The pathway used when oxygen is limited, converting pyruvate to lactate to regenerate $NAD^+$ for the continued operation of glycolysis.

Lactate dehydrogenase

A reversible enzyme that converts pyruvate and $NADH + H^+$ into lactate and $NAD^+$ under anaerobic conditions.

Net ATP yield of glycolysis

The total energy gain from one glucose molecule in glycolysis, which is $2\,ATP$ (4 produced minus 2 invested).

Allosteric regulation of PFK

A control mechanism where ATP and citrate act as inhibitors at a regulatory site, while AMP acts as an activator to increase the reaction rate.

Red blood cells (RBCs)

Cells that rely on glycolysis as their only pathway for ATP production because they lack mitochondria.

Warburg effect

The observation that tumor cells preferentially generate energy through anaerobic glycolysis and produce lactate at high rates even when oxygen is present.