Cellular Energy, Respiration, and Metabolism

Comprehensive vocabulary flashcards covering glycolysis, the Krebs cycle, electron transport, oxidative phosphorylation, mitochondrial structure, and fermentation.

Adult Stored Energy Reserve

A healthy adult stores approximately $500\,MJ$ of energy (equivalent to about $3.7\text{ gallons}$ of gasoline), which provides sufficient energy to survive for roughly $40\text{ days}$ given access to water.

Core Respiration Equation

$C_6H_{12}O_6 + 6O_2 + ADP \rightleftharpoons 6CO_2 + 6H_2O + ATP$, representing the breakdown of carbohydrate with oxygen gas and ADP to yield carbon dioxide, water, and ATP.

Cyclic-AMP (cAMP)

A modified form of adenosine monophosphate (AMP) that functions as a cellular signaling molecule indicating starvation.

GLUT Transporter

A membrane channel protein that mediates uncoupled transport of glucose into the cell passively by following its concentration gradient.

Coupled Glucose Transport

Active transport of glucose across the plasma membrane against its concentration gradient, powered by coupling with an electrochemical gradient maintained by the $Na^+/K^+$ pump.

Glycolysis

The metabolic pathway occurring in the cytoplasm consisting of three main phases: glucose activation/capture, sugar splitting, and energy generation.

Glucose Activation Phase

The initial phase of glycolysis where glucose is phosphorylated ('tagged') using $2\text{ molecules of } ATP$, which traps the molecule inside the cell.

Fructose 1,6-bisphosphate

The double-tagged six-carbon intermediate formed during Phase 1 of glycolysis prior to cleavage.

Glyceraldehyde-3-phosphate

The three-carbon phosphorylated sugar produced when fructose 1,6-bisphosphate is cleaved during Phase 2 of glycolysis.

Net Outputs of Glycolysis

Per molecule of glucose, glycolysis yields a net of $2\text{ molecules of } ATP$ (for energy), $2\text{ molecules of } NADH$ (to fuel the ETC), and $2\text{ molecules of pyruvate}$ (to fuel the Krebs cycle).

Outer Mitochondrial Membrane (OMM)

The external layer of the mitochondrion's double membrane structure, characterized by being porous.

Inner Mitochondrial Membrane (IMM)

The tightly sealed internal membrane of the mitochondrion that does not allow simple diffusion, creating a barrier essential for proton gradient establishment.

Mitochondrial DNA (mtDNA)

Autonomous, circular genetic material present inside mitochondria that encodes specific mitochondrial proteins, tRNAs, and rRNAs.

Krebs Cycle (Citric Acid Cycle)

A cyclic metabolic pathway in the mitochondrial matrix that takes in carbon from pyruvate, releases $CO_2$ as waste, and yields $3\,NADH$, $1\,FADH_2$, and $1\,ATP$ per pyruvate molecule.

Electron Transport Chain (ETC)

A membrane-bound assembly of complexes (I, II, III, IV) and mobile carriers (CoQ, Cyt c) that transfers electrons and pumps hydrogen ions ($H^+$) into the intermembrane space.

Final Electron Acceptor

Molecular oxygen ($O_2$), which binds electrons and free protons at Complex IV of the electron transport chain to form $H_2O$.

Proton-Motive Force (PMF) Energy Conversion

The sequential energy transformation sequence that drives ATP synthesis: $H^+\text{-gradient} \rightarrow \text{rotational energy} \rightarrow \text{chemical energy}$.

ATP Synthase

A multi-protein rotary nano-machine consisting of a membrane-embedded rotor ($F_0$ ring) and a catalytic stator ($F_1$ ATPase head) driven by proton flow to synthesize ATP from $ADP + P_i$.

Theoretical vs. Real-World ATP Yield

Aerobic respiration has a theoretical maximum of $38\,ATP$ per glucose molecule, but real-world yield is closer to $30\,ATP$ because most energy is dissipated as heat.

Lactic Acid Fermentation

An anaerobic process in animals where pyruvate is converted to lactate to regenerate $NAD^+$ from $NADH$, allowing glycolysis to continue in the absence of $O_2$.

Ethanol Fermentation

An anaerobic metabolic pathway utilized by yeast where pyruvate is converted to ethanol and carbon dioxide to regenerate $NAD^+$ for glycolysis.