Brock Biology of Microorganisms - Chapter 3: Microbial Metabolism

Vocabulary flashcards focusing on key definitions, metabolic classes, pathways, enzymes, energetics, and cellular biosynthesis from Chapter 3 of Brock Biology of Microorganisms.

Metabolism

The sum total of all biochemical reactions needed for life, consisting of catabolism (obtaining energy) and anabolism (making cellular material).

Catabolism

Exergonic cellular processes that break down chemicals to generate free energy, which is conserved by synthesizing energy-rich molecules such as ATP.

Anabolism

Endergonic cellular processes in which cellular synthesis requires energy input derived from the hydrolysis of ATP.

Free Energy ($\Delta G^{0\prime}$)

The energy available to do work under standard conditions ($pH\,7$, $25\,^\circ\text{C}$, $1\,\text{atm}$, and $1\,\text{M}$ reactant/product concentrations).

Exergonic Reaction

A chemical reaction that releases energy and has a negative change in free energy ($-\Delta G^{0\prime}$).

Endergonic Reaction

A chemical reaction that requires or absorbs energy and has a positive change in free energy ($+\Delta G^{0\prime}$).

Reducing Power

The capability of a molecule to donate electrons during electron transfer reactions (oxidation-reduction reactions).

Electron Donor

A substance that loses electrons and becomes oxidized during a redox reaction.

Electron Acceptor

A substance that gains electrons and becomes reduced during a redox reaction.

Phototrophs

Organisms that convert light into energy and do not require chemical energy sources.

Chemotrophs

Organisms that obtain energy from chemical reactions involving organic or inorganic compounds.

Chemoorganotrophs

Organisms that obtain energy and reducing power from organic compounds.

Chemolithotrophs

Organisms that obtain energy and reducing power from inorganic compounds.

Heterotrophs

Organisms that obtain their cellular carbon from organic compounds.

Autotrophs

Organisms that obtain cellular carbon from carbon dioxide ($\text{CO}_2$), acting as primary producers.

Reduction Potential ($E_0'$)

The measure of the inherent affinity of a substance for electrons, expressed in volts ($\text{V}$).

The Redox Tower

A visual representation ranking redox couples according to their reduction potentials ($E_0'$), where substances at the top donate electrons to substances lower down to release free energy.

Substrate-Level Phosphorylation

A mechanism of ATP synthesis in which a high-energy phosphate bond on an organic substrate is directly hydrolyzed to drive the phosphorylation of ADP.

Oxidative Phosphorylation

A mechanism of ATP synthesis driven by the movement of electrons through an electron transport chain to generate a proton motive force.

Photophosphorylation

The production of ATP using a proton motive force generated by light-driven electron transport.

Activation Energy

The minimum quantity of energy required for molecules to reach a reactive state and undergo a chemical reaction.

Enzyme

A biological catalyst, typically a protein or RNA molecule, that lowers the activation energy of a reaction to increase its rate without being consumed.

Active Site

The specific region of an enzyme that binds substrate molecules and facilitates the chemical catalysis.

Glycolysis

A near-universal metabolic pathway (EMP pathway) that oxidizes glucose to pyruvate, generating a net yield of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Citric Acid Cycle (CAC)

A metabolic pathway that decarboxylates and oxidizes pyruvate (via acetyl-CoA) completely to $\text{CO}_2$, yielding $\text{NADH}$, $\text{FADH}_2$, ATP/GTP, and biosynthetic precursors.

Fermentation

An anaerobic catabolic pathway in which organic compounds act as both electron donors and acceptors, relying on substrate-level phosphorylation to harvest energy.

Respiration

A catabolic pathway where electrons are transferred from an electron donor through a membrane-bound transport chain to an external terminal electron acceptor.

Proton Motive Force (PMF)

An electrochemical gradient established across the cytoplasmic membrane by the pumping of protons ($\text{H}^+$) outside the cell during electron transport.

ATP Synthase

A conserved multiprotein complex consisting of $F_1$ and $F_0$ components that uses mechanical energy from the proton motive force to synthesize ATP from ADP and $P_i$.

Nitrogen Fixation

The energy-demanding process of reducing gaseous dinitrogen ($\text{N}_2$) into ammonia ($\text{NH}_3$), requiring $16\,\text{ATP}$ and catalyzed by the nitrogenase complex.

Nitrogenase

An oxygen-sensitive enzyme complex consisting of dinitrogenase and dinitrogenase reductase that contains an iron-molybdenum cofactor (FeMo-co) to catalyze $\text{N}_2$ reduction.

Heterocyst

A specialized cell formed in filamentous cyanobacteria that maintains an anoxic interior to protect oxygen-sensitive nitrogenase during nitrogen fixation.

Gluconeogenesis

The metabolic pathway responsible for synthesizing glucose starting from phosphoenolpyruvate (PEP).

Pentose Phosphate Pathway

A major pathway that oxidizes glucose to generate $\text{C}_5$ sugars (pentoses) for nucleic acid synthesis, as well as $\text{NADPH}$ for biosynthetic reactions.

Acyl Carrier Protein (ACP)

A specialized protein that anchors and holds the growing fatty acid chain during fatty acid biosynthesis.