Metabolic Pathways: Glycolysis and Energy Production

Gibbs free energy change (ΔG°) for complete glucose oxidation

−2834 kJ/mol.

negative ΔG°

The reaction is exergonic (spontaneous and releases energy).

positive ΔG°

The reaction is endergonic (requires energy input).

formula linking ΔG and ΔG°

ΔG = ΔG° + RT lnQ

ΔG = 0

The reaction is at equilibrium.

endergonic reactions coupled to exergonic ones

To make them energetically favorable.

reaction coupling glucose phosphorylation to ATP hydrolysis

Glucose + ATP → Glucose-6-P + ADP (ΔG° = −17 kJ/mol)

irreversible steps in glycolysis

Three.

enzyme for the first irreversible step of glycolysis

Hexokinase (Glucose → Glucose-6-phosphate).

enzyme for the second irreversible step

Phosphofructokinase (F6P → F1,6-BP).

enzyme for the third irreversible step

Pyruvate kinase (PEP → Pyruvate).

steps in glycolysis generating ATP

1. 1,3-BPG → 3-PG (phosphoglycerate kinase), 2. PEP → Pyruvate (pyruvate kinase).

coenzyme involved in redox reactions in glycolysis

NAD⁺ / NADH.

how is pyruvate converted back to PEP in gluconeogenesis

Via pyruvate carboxylase and PEP carboxykinase (requires ATP & GTP).

why is gluconeogenesis energetically possible

Use of new enzymes and coupling with ATP/GTP hydrolysis.

feedback inhibition

End product inhibits an earlier step to regulate pathway activity.

gene regulation affects metabolism

Controls enzyme levels for long-term metabolic control.

function of enzyme isoforms (e.g., glucokinase)

Tissue-specific regulation of metabolism.

net ATP yield per glucose molecule in glycolysis

2 ATP (4 produced, 2 used in priming).

how many NADH molecules are generated per glucose in glycolysis

2 NADH.

three irreversible steps in glycolysis

1. Glucose → Glucose-6-P (hexokinase)
2. Fructose-6-P → Fructose-1,6-BP (PFK-1)
3. PEP → Pyruvate (pyruvate kinase).

which enzyme converts glyceraldehyde-3-P to 1,3-bisphosphoglycerate

Glyceraldehyde-3-phosphate dehydrogenase (G3PDH).

what bond forms between G3P dehydrogenase and its substrate in Step 1

Thioether bond (enzyme-SH + substrate).

why is NAD+ essential in glycolysis

It acts as an electron carrier (oxidized to NADH in G3PDH reaction).

pyruvate under AEROBIC conditions in eukaryotes

Enters mitochondria → acetyl-CoA via PDH complex (linked to TCA cycle).

why is lactate produced under anaerobic conditions

To regenerate NAD+ for glycolysis to continue.

which organism uses alcoholic fermentation

Yeast (pyruvate → ethanol + CO₂).

pyruvate dehydrogenase (PDH) complex

Converts pyruvate → acetyl-CoA + NADH + CO₂ (link reaction).

where is the PDH complex in eukaryotes

Mitochondrial matrix.

pyruvate crosses the inner mitochondrial membrane

Via MPC (mitochondrial pyruvate carrier).

Coenzyme A's (CoA) role

Carries acetyl groups (forms acetyl-CoA for TCA cycle).

energy equivalent of 2 NADH from glycolysis

~6 ATP (via ETC; 3 ATP/NADH).

why do RBCs only perform anaerobic glycolysis

Lack mitochondria (must deliver O₂ to other tissues).

where does TCA cycle occur in prokaryotes

Cytoplasm (no mitochondria).

where is the ETC in eukaryotes

Inner mitochondrial membrane.