Fermentation

ATP Yield and Accounting in Cellular Respiration

• Standard Conversion Rates for Electron Carriers:

  • Each $\text{NADH}$ molecule yields $3\text{ ATP}$, with the exception of $\text{NADH}$ produced during glycolysis, which yields either $2\text{ ATP}$ or $3\text{ ATP}$.

  • Each $\text{FADH}_2$ molecule yields $2\text{ ATP}$.

• Cycle Multiplier:

  • Respiration steps following glycolysis happen $2\text{ times}$ per initial single molecule of glucose.

• Substrate-Level Phosphorylation:

  • Glycolysis produces a net direct yield of $2\text{ ATP}$ via substrate-level phosphorylation.

  • The Citric Acid Cycle produces a net direct yield of $2\text{ ATP}$ via substrate-level phosphorylation.

• Detailed Breakdown of ATP Production per Glucose Molecule:

  • Glycolysis:

  • Substrate-level phosphorylation: $2\text{ ATP}$.

  • Yield from $2\text{ NADH}$: Since glycolysis $\text{NADH}$ produces $2$ or $3\text{ ATP}$ per carrier, $2\text{ NADH} \times 2 = 4\text{ ATP}$ or $2\text{ NADH} \times 3 = 6\text{ ATP}$.

  • Pyruvate to Acetyl-CoA (Transition Step):

  • Yield from $2\text{ NADH}$: $2\text{ NADH} \times 3 = 6\text{ ATP}$.

  • Citric Acid Cycle:

  • Substrate-level phosphorylation: $2\text{ ATP}$.

  • Yield from $6\text{ NADH}$: $6\text{ NADH} \times 3 = 18\text{ ATP}$.

  • Yield from $2\text{ FADH}_2$: $2\text{ FADH}_2 \times 2 = 4\text{ ATP}$.

• Total Accumulated ATP Accounting:

  • Subtotal from Citric Acid Cycle electron carriers alone: $18\text{ ATP (from NADH)} + 4\text{ ATP (from FADH}_2) = 22\text{ ATP}$.

  • Intermediate cumulative total ("so far"): $22\text{ ATP}$ to $30\text{ ATP}$.

  • Total potential overall yield across all stages: $32\text{ ATP}$ to $36\text{ ATP}$.

Regulation of Glycolysis: Phosphofructokinase and Allosteric Control

• Key Regulatory Enzyme:

  • Phosphofructokinase (phospho fructokinase) is the primary enzyme responsible for regulating the rate of glycolysis.

  • Substrate: Fructose-6-phosphate.

• Feedback Inhibition under High ATP Conditions:

  • High amounts of ATP trigger feedback inhibition to prevent the unnecessary breakdown of glucose.

  • ATP binds to an allosteric site on phosphofructokinase.

  • Upon binding, the enzyme changes shape, which blocks it from splitting its substrate, fructose-6-phosphate.

• Activation under Low ATP / High Energy Demand:

  • Energy is released when the ATP bond is broken ($-32\text{ kJ}$ or $-30\text{ kJ}$ released, indicating the energy needed for cellular completion work).

  • When cellular ATP is depleted, high concentrations of ADP and AMP accumulate.

  • High amounts of AMP serve as a signal that the cell is in trouble due to low energy reserves.

  • AMP acts as an activator: AMP binds to a separate allosteric site on phosphofructokinase, activating the enzyme to resume or accelerate glycolysis.

Anaerobic Respiration and Fermentation Pathways

• Definitions:

  • Aerobic: Respiration processes that utilize oxygen.

  • Anaerobic: Respiration pathways that generate ATP without oxygen.

• Alcohol (Ethanol) Fermentation in Yeast:

  • Chemical Reaction Equation: $\text{Glucose} \rightarrow \text{Ethanol} + \text{CO}_2 + 2\text{ ATP}$

  • Path Characteristics:

  • Only proceeds as far as glycolysis.

  • Occurs without oxygen and does not utilize mitochondria.

  • Recycles $\text{NADH}$ generated during glycolysis back to $\text{NAD}^+$.

  • Gas Production:

  • Produces carbon dioxide ($\text{CO}_2$) gas.

  • The rising bubbles of $\text{CO}_2$ gas create holes in bread dough.

• Lactic Acid Fermentation in Animals:

  • Chemical Reaction Equation: $\text{Glucose} \rightarrow \text{Lactate (Lactic Acid)} + 2\text{ ATP}$

  • Path Characteristics:

  • Mechanism for respiration without oxygen in animal cells.

  • Unlike yeast fermentation, animals do not make $\text{CO}_2$ during lactic acid fermentation.

  • Physiological Impact:

  • Lactic acid buildup affects intracellular and tissue pH.

  • Alterations in pH directly affect protein and enzyme function in muscle tissue.

Additional Marginalia and Operational Notes

• Recorded Numerical and Procedural Annotations:

  • Date annotation: 9/21/20.

  • Recorded values and step markers: 24, 1, 2, 24, H, 2.

  • Operational instruction note: "Do this around 18 or 19 trans".