Cellular Respiration: Energy Harvest, Glycolysis, and Fermentation

Vocabulary practice flashcards covering fundamental concepts, pathways, energetics, and mechanisms of cellular respiration, glycolysis, pyruvate oxidation, and anaerobic pathways.

Autotrophs

Organisms that are able to produce their own organic molecules through photosynthesis.

Heterotrophs

Organisms that live on organic compounds produced by other organisms.

Cellular Respiration

A series of reactions that all organisms use to extract energy from organic molecules.
Glucose (C₆H₁₂O₆) + Oxygen (6O₂) → Carbon Dioxide (6CO₂) + Water (6H₂O) + ATP

Oxidation

A chemical reaction involving the loss of electrons.

Reduction

A chemical reaction involving the gain of electrons.

Dehydrogenation

A reaction in which lost electrons are accompanied by protons, resulting in the net loss of a hydrogen atom ($1$ electron and $1$ proton).

Nicotinamide Adenine Dinucleotide ($\text{NAD}^+$)

An electron carrier and enzymatic cofactor that reversibly accepts two electrons and $1$ proton to become NADH.

Aerobic Respiration

A form of cellular respiration in which the final electron acceptor is oxygen ($\text{O}_2$).

Anaerobic Respiration

A form of cellular respiration in which the final electron acceptor is an inorganic molecule other than oxygen ($\text{O}_2$), such as sulfur, nitrate, carbon dioxide, or inorganic metals.

Fermentation

The anaerobic process where carbs are broken down into NAD+

Free Energy of Glucose Oxidation

The total free energy released from the complete reaction $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Energy}$, equal to $-686\,\text{kcal/mol}$ of glucose (or higher in a cell).

Free Energy of ATP Hydrolysis ($\Delta G$)

The free energy released when hydrolyzing the terminal phosphate group of ATP to drive endergonic reactions, equal to $-7.3\,\text{kcal/mol}$.

Substrate-Level Phosphorylation

A mechanism of ATP synthesis where a phosphate group is transferred directly from a substrate molecule to ADP, Ex. glycolysis.

Oxidative Phosphorylation

Final step of cellular respiration - electron carriers make water, and then chemiosmosis happens, and ATP is formed.

Glycolysis

A $10$-step biochemical pathway occurring in the cytoplasm that converts $1$ glucose ($6$ carbons) into $2$ pyruvate ($3$ carbons), yielding a net of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Priming Reactions

The initial phase of glycolysis in which two high-energy phosphates from two molecules of ATP are added to a $6$-carbon glucose molecule, producing a $6$-carbon sugar diphosphate.

Cleavage (in Glycolysis)

The second phase of glycolysis where the $6$-carbon sugar diphosphate is split in two, forming two $3$-carbon sugar phosphates.

Oxidation and ATP Formation (in Glycolysis)

Inorganic phosphorylation happens, oxidation produces NADH, and high-energy phosphates are transferred to ADP to yield a net energy of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Methanogens

Diverse organisms (including those found in cows) that perform anaerobic respiration by reducing $\text{CO}_2$ to $\text{CH}_4$ (methane).

Sulfur Prokaryotes

Organisms that carry out anaerobic respiration by reducing inorganic sulfate ($\text{SO}_4$) to hydrogen sulfide ($\text{H}_2\text{S}$), setting the stage for the evolution of photosynthesis.

Ethanol Fermentation

Fermentation in yeast, where pyruvate is converted to acetaldehyde (decarboxylation) and then to ethanol, producing ethanol and regenerating NAD+.
Glucose yields Ethanol + CO2 + NAD+

Lactic Acid Fermentation

In animal cells (especially muscles) and some bacteria where electrons from NADH are transferred to pyruvate to produce lactate (lactic acid) and regenerate $\text{NAD}^+$.

Pyruvate Oxidation

A stage of aerobic respiration occurring in the mitochondrial matrix of eukaryotes (and plasma membrane of prokaryotes) where pyruvate is converted to acetyl-CoA.

Pyruvate Dehydrogenase

The multi-enzyme complex that catalyzes the decarboxylation and oxidation of pyruvate into acetyl-CoA, $\text{CO}_2$, and NADH.

Acetyl-CoA (Acetyl Coenzyme A)

A molecule consisting of two carbons from pyruvate linked to coenzyme A, which enters the citric acid cycle after pyruvate oxidation.