Energy in Living Organisms: Respiration and ATP Synthesis

Vocabulary flashcards reviewing ATP structure and function, mitochondrial structure, glycolysis enzymes and steps, link reaction, Krebs cycle, electron transport chain, ATP yield calculation, and fermentation pathways.

Adenosine Triphosphate (ATP)

A nucleotide molecule composed of adenine, ribose sugar, and three phosphate groups that acts as a temporary energy store in living organisms.

Hydrolysis of ATP

An exergonic reaction in which a phosphate group is removed from ATP to form ADP and inorganic phosphate ($P_i$), releasing approximately $30.5\,kJ\,mol^{-1}$ to $31\,kJ\,mol^{-1}$ of energy.

ATP Synthase

A protein channel and enzyme embedded in membranes that transfers energy from $H^+$ ions moving down their electrochemical gradient to synthesize ATP from ADP and $P_i$.

Mitochondria Structural Features

The structural components of the mitochondrion, including the outer membrane, inner membrane, inner membrane folds called cristae, and the internal fluid matrix.

Glycolysis

The metabolic pathway in the cytosol meaning 'sugar-breaking' where one 6-carbon glucose molecule is broken down into two 3-carbon pyruvate molecules, yielding a net of $2\,ATP$ and $2\,NADH$.

Hexokinase

The enzyme catalyzing Step 1 of glycolysis, transferring a phosphate group from ATP to glucose to form glucose-6-phosphate.

Phosphoglucoisomerase

The enzyme catalyzing Step 2 of glycolysis, which rearranges glucose-6-phosphate into its isomer, fructose-6-phosphate.

Phosphofructokinase

The enzyme catalyzing Step 3 of glycolysis, which uses a second ATP molecule to phosphorylate fructose-6-phosphate to fructose-1,6-bisphosphate.

Aldolase

The enzyme catalyzing Step 4 of glycolysis, splitting fructose-1,6-bisphosphate into two 3-carbon sugars: glyceraldehyde-3-phosphate (GALP) and dihydroxyacetone phosphate (DHAP).

Enolase

The enzyme catalyzing Step 9 of glycolysis, which removes a molecule of water from 2-phosphoglycerate to form phosphoenolpyruvate (PEP).

Pyruvate Kinase

The enzyme catalyzing Step 10 of glycolysis, transferring a phosphate group from phosphoenolpyruvate (PEP) to ADP to form ATP and pyruvate.

Link Reaction

The oxidative decarboxylation process occurring in the mitochondrial matrix that converts pyruvate into acetyl CoA, yielding $2\text{ acetyl CoA}$, $2\,NADH$, and $2\,CO_2$ per glucose molecule.

Krebs Cycle

An 8-step cyclic sequence of enzymatic reactions in the mitochondrial matrix that oxidizes acetyl CoA, generating $2\,ATP$, $6\,NADH$, $2\,FADH_2$, and $4\,CO_2$ per glucose molecule (across 2 turns).

Electron Transport Chain (ETC)

A series of four protein complexes embedded in the inner mitochondrial membrane that transfer electrons from high energy levels to lower energy levels, generating a proton gradient across the membrane.

Complex I (NADH - Ubiquinone Oxidoreductase)

The first large protein complex of the electron transport chain that accepts electrons specifically from NADH molecules produced during glycolysis, the link reaction, and the Krebs cycle.

Complex II (Succinate - Ubiquinone Reductase)

The protein complex of the electron transport chain that accepts electrons specifically from $FADH_2$ produced during the Krebs cycle.

Oxygen in Cellular Respiration

The final electron acceptor in the electron transport chain, which combines with two electrons and two protons ($H^+$) to form water ($2e^- + 2H^+ + \frac{1}{2}O_2 \rightarrow H_2O$).

Recalculated Net ATP Yield

The realistic total net gain of $32\,ATP$ produced per glucose molecule during aerobic respiration, based on reduced NAD producing $2.5\,ATP$ ($10 \times 2.5 = 25$) and reduced FAD producing $1.5\,ATP$ ($2 \times 1.5 = 3$).

Alcoholic Fermentation

An anaerobic pathway occurring in yeast and plant cells where pyruvate is decarboxylated to acetaldehyde and then reduced by NADH to ethanol, generating $2\,ATP$ and $2\,CO_2$ per glucose.

Lactic Acid Fermentation

An anaerobic pathway occurring in animal muscle cells where pyruvate is directly reduced by NADH to lactate, regenerating $NAD^+$ and producing $2\,ATP$ per glucose.

Substrate-Level Phosphorylation

The mode of ATP synthesis where a phosphate group is directly transferred from a phosphorylated metabolic intermediate to ADP (or GDP) to form ATP (or GTP).