Microbial Metabolism

Vocabulary practice flashcards covering fundamental concepts of microbial metabolism, including enzyme function and regulation, carbohydrate catabolism, cellular respiration, fermentation, and biosynthetic pathways.

Anabolic Pathways

Metabolic pathways that synthesize large macromolecules from smaller precursor products of catabolism; these reactions are endergonic, requiring more energy than they release.

Oxidation-Reduction (Redox) Reactions

Coupled chemical reactions in which electrons are transferred simultaneously from an electron donor (which becomes oxidized) to an electron acceptor (which becomes reduced).

Phosphorylation

The metabolic addition of inorganic phosphate ($P_i$) to an organic substrate, occurring in cells via substrate-level phosphorylation, oxidative phosphorylation, or photophosphorylation.

Activation Energy

The amount of energy required to initiate a chemical reaction; enzymes increase reaction rates by lowering this energetic barrier.

Hydrolase

A class of enzymes that catalyzes catabolic hydrolysis reactions by adding water to cleave larger molecules into smaller parts (e.g., lipase).

Isomerase

A class of enzymes that catalyzes the rearrangement of atoms within a molecule without adding or removing atoms, being neither catabolic nor anabolic (e.g., phosphoglucoisomerase).

Ligase (Polymerase)

A class of enzymes that catalyzes anabolic reactions joining two or more chemical molecules together using energy (e.g., acetyl-CoA synthetase).

Lyase

A class of enzymes that catalyzes the splitting of a chemical molecule into smaller parts without using water in a catabolic manner (e.g., fructose-1,6-bisphosphate aldolase).

Oxidoreductase

A class of enzymes that catalyzes the transfer of electrons or hydrogen atoms from one molecule to another (e.g., lactic acid dehydrogenase).

Transferase

A class of enzymes that moves a specific functional chemical group from one molecule to another (e.g., hexokinase transferring phosphate to glucose).

Apoenzyme

The protein portion of an enzyme that remains catalytically inactive unless bound to one or more nonprotein cofactors.

Holoenzyme

The complete, catalytically active enzyme formed by the binding of an apoenzyme (protein component) with its requisite inorganic or organic cofactor(s).

Ribozyme

An RNA molecule that functions as a biological catalyst rather than a protein enzyme.

Competitive Inhibitor

An inhibitory substance shaped similarly to an enzyme's normal substrate that binds directly to the active site, competitively blocking substrate binding without denaturing the protein.

Allosteric (Noncompetitive) Inhibition

Enzymatic inhibition occurring when an inhibitor binds to an allosteric site rather than the active site, inducing a conformational change that distorts the active site and prevents substrate binding.

Feedback Inhibition

A regulatory mechanism in which the accumulated end-product of a metabolic pathway binds allosterically to an enzyme early in the pathway, shutting down further synthesis.

Glycolysis

A 10-step catabolic pathway occurring in the cytoplasm that splits a six-carbon glucose molecule into two three-carbon pyruvic acid molecules, yielding a net of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Substrate-Level Phosphorylation

The direct enzymatic transfer of a phosphate group from a phosphorylated organic metabolic substrate to ADP, forming ATP without requiring a proton gradient.

Krebs Cycle

A circular series of eight metabolic reactions occurring in the prokaryotic cytosol or eukaryotic mitochondrial matrix that completely oxidizes acetyl groups, producing $2\,\text{ATP}$, $6\,\text{NADH}$, $2\,\text{FADH}_2$, and $4\,\text{CO}_2$ per glucose molecule.

Electron Transport Chain (ETC)

A membrane-bound sequence of redox carrier molecules (flavoproteins, ubiquinones, metal-containing proteins, and cytochromes) that pass electrons to a final acceptor while pumping protons ($H^+$) across the membrane.

Chemiosmosis

The mechanism of ATP synthesis in which the potential energy of a transmembrane electrochemical proton gradient (proton motive force) drives the phosphorylation of ADP to ATP via ATP synthase.

Pentose Phosphate Pathway

An alternative pathway to glycolysis that produces pentose sugars, provides $2\,\text{NADPH}$ for anabolic reactions, and yields precursor metabolites such as ribose 5-phosphate and erythrose 4-phosphate.

Entner-Doudoroff Pathway

An alternate catabolic pathway that catabolizes glucose to pyruvic acid using different enzymes than glycolysis, producing $1\,\text{ATP}$, $1\,\text{NADH}$, and $1\,\text{NADPH}$ per glucose molecule.

Fermentation

The partial oxidation of sugar or other metabolites to release energy using an endogenous organic molecule as the final electron acceptor, primarily serving to regenerate $NAD^+$ in the absence of cellular respiration.

Beta-Oxidation

A catabolic pathway that systematically cleaves fatty acid chains into two-carbon acetyl-CoA units, generating $FADH_2$ and $NADH$ to feed into cellular respiration.

Deamination

The enzymatic removal of an amino group ($-NH_2$) from an amino acid, allowing the remaining carbon skeleton to enter the Krebs cycle as an energy source or precursor metabolite.

Chlorophyll

A light-harvesting pigment molecule consisting of a hydrophobic hydrocarbon tail anchored in a membrane and a light-absorbing porphyrin active site centered around a magnesium ion ($Mg^{2+}$).

Thylakoid

A specialized cellular membrane hosting photosystems and light-dependent reactions, formed by infoldings of the cytoplasmic membrane in prokaryotes or inner chloroplast membranes in eukaryotes.

Calvin-Benson Cycle

The light-independent pathway of photosynthesis that utilizes $ATP$ and $NADPH$ to fix carbon dioxide ($CO_2$) into glyceraldehyde 3-phosphate (G3P) and synthesize glucose.

Amphibolic Pathway

A reversible metabolic pathway that can function in both catabolic (degradative) and anabolic (synthetic) directions depending on cellular needs.

Gluconeogenesis

An anabolic pathway that synthesizes hexose sugars, such as glucose, from non-carbohydrate precursor metabolites including pyruvic acid, glycerol, and oxaloacetic acid.

Transamination

A biochemical reaction in which an amine group ($-NH_2$) is transferred from an amino acid to a keto acid precursor (such as oxaloacetate or $\alpha$-ketoglutarate) to synthesize a new amino acid.