Biol 1081 Study Sheet | Ch 7 - Cellular Respiration

Autotroph

An organism that synthesizes its own organic food molecules from inorganic substances using light or chemical energy.

Heterotroph

An organism that obtains organic food molecules and energy by consuming other organisms or organic substances.

Overall chemical equation for cellular respiration

$$C<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6CO<em>2 + 6H</em>2O + \text{ATP}$$

Substrate-level phosphorylation

The formation of ATP by the direct enzymatic transfer of a phosphate group from a phosphorylated metabolic intermediate to ADP.

Oxidative phosphorylation

The synthesis of ATP powered by the redox reactions of the electron transport chain and coupled to chemiosmosis.

Oxidation vs. reduction

Oxidation involves the loss of electrons or hydrogen atoms, whereas reduction involves the gain of electrons or hydrogen atoms.

Structural components of an ATP molecule

Adenine (nitrogenous base), ribose (five-carbon sugar), and three phosphate groups linked by two high-energy phosphoanhydride bonds.

Four stages of aerobic cellular respiration

1. Glycolysis, 2. Pyruvate oxidation, 3. Citric acid cycle (Krebs cycle), and 4. Oxidative phosphorylation.

Role of molecular oxygen ($O_2$) in aerobic respiration

Serves as the final electron acceptor of the electron transport chain, combining with electrons and protons to form $H_2O$.

Proton-motive force

The electrochemical potential energy stored across the inner mitochondrial membrane due to the accumulation of hydrogen ions ($H^+$) in the intermembrane space.

Chemiosmosis

The process by which energy stored in a transmembrane proton gradient drives the phosphorylation of ADP to form ATP via ATP synthase.

Uncoupling protein

A mitochondrial channel protein that allows protons to diffuse back into the matrix without passing through ATP synthase, dissipating energy as heat instead of ATP.

Lactic acid fermentation vs. alcohol fermentation

Lactic acid fermentation reduces pyruvate to lactate without producing carbon dioxide, whereas alcohol fermentation converts pyruvate into ethanol and releases $CO_2$.

Pyruvate

A three-carbon organic acid produced at the end of glycolysis that enters the mitochondrion for further oxidation.

Acetyl CoA

A two-carbon functional group linked to coenzyme A, formed by the oxidation of pyruvate before entering the citric acid cycle.

Electron transport chain (ETC)

A sequence of protein complexes embedded in the inner mitochondrial membrane that transfer electrons via redox reactions to establish a proton gradient.

ATP synthase enzyme

A membrane-bound protein complex that utilizes the proton-motive force across the inner mitochondrial membrane to catalyze the synthesis of ATP from ADP and inorganic phosphate.

Cellular locations of the four stages of aerobic respiration

Glycolysis takes place in the cytosol, pyruvate oxidation and the citric acid cycle occur in the mitochondrial matrix, and oxidative phosphorylation occurs across the inner mitochondrial membrane.

Stage of cellular respiration that requires an initial input of ATP

Glycolysis, which uses an investment of $2\,\text{ATP}$ in its initial preparatory reactions.

Anaerobic metabolism

Cellular pathways that extract chemical energy from organic nutrients in the absence of molecular oxygen ($O_2$).

Anaerobic cellular respiration vs. fermentation

Anaerobic respiration utilizes an electron transport chain with an inorganic final electron acceptor other than oxygen, whereas fermentation does not use an electron transport chain and relies on organic molecules to accept electrons from $NADH$.

Two sequential steps of anaerobic energy pathways (fermentation)

1. Glycolysis, which produces pyruvate, $2\text{ ATP}$, and $2\text{ NADH}$; and 2. Fermentation, which regenerates $NAD^+$ by reducing pyruvate or one of its derivatives.

Reason $NADH$ generates more ATP than $FADH_2$

Electrons from $NADH$ enter Complex I of the electron transport chain at a higher energy state, driving more proton pumping than electrons from $FADH_2$, which enter downstream at Complex II.

Reasons ATP yield from cellular respiration is expressed as a range

The electrochemical proton gradient is also used to drive other transport processes, the cytosolic $NADH$ shuttle mechanisms into the mitochondrion differ in efficiency, and the ratio of protons pumped to ATP synthesized is not a whole number.

Biomolecules used as metabolic fuel for cellular respiration and the class that yields the most ATP

Carbohydrates, fats (lipids), and proteins can all be oxidized for energy; fats yield the most ATP per gram because they are in a more highly reduced state with abundant hydrogen atoms.

Two direct products of the electron transport chain

Water ($H_2O$) and the electrochemical proton gradient across the inner mitochondrial membrane.