Microbial Metabolism and Enzymatic Processes

Vocabulary flashcards covering topics from microbial metabolism, including metabolic pathways, enzyme mechanics, ATP generation, cellular respiration, fermentation, and pathogen requirements.

Metabolism

The sum of all chemical reactions that take place within the cells of an organism, the ultimate goal of which is to reproduce the organism.

Catabolism

The phase of metabolism involving exergonic reactions that break down large complex molecules into smaller ones, releasing energy that is stored as ATP.

Anabolism

The phase of metabolism involving endergonic reactions that build large complex molecules from smaller ones using energy supplied by ATP.

Metabolic pathway

A sequence of enzymatically catalyzed chemical reactions occurring in a cell, determined by specific enzymes encoded by genes.

Enzyme

A biological catalyst, almost always a protein, that speeds up a chemical reaction without being consumed or permanently changed.

Apoenzyme

The protein portion of an enzyme that is inactive by itself without its required cofactor.

Cofactor

A non-protein component, such as a metal ion, required for certain enzymes to function.

Coenzyme

An organic cofactor, such as a vitamin, that assists enzyme activity.

Holoenzyme

A complete, active enzyme consisting of an apoenzyme bound to its cofactor.

Active site

The specific region of an enzyme where the substrate binds and the chemical reaction occurs.

Enzyme-substrate complex

The temporary complex formed when a substrate molecule binds to an enzyme's active site.

Activation energy

The minimum energy required for a chemical reaction to begin, which is lowered by enzymes.

Exoenzymes

Enzymes that are secreted outside of the cell to break down molecules in the extracellular environment.

Endoenzymes

Enzymes that function inside the cell.

Competitive inhibitor

A substance that decreases enzyme activity by competing directly with the substrate for binding at the active site.

Noncompetitive inhibitor

A substance that decreases enzyme activity by binding to an allosteric site, altering the shape of the active site so the substrate cannot bind.

Allosteric site

A site on an enzyme other than the active site where regulatory molecules or noncompetitive inhibitors bind.

Feedback inhibition

A regulatory mechanism where the end product of a metabolic pathway binds to the allosteric site of an earlier enzyme to shut down the pathway.

Oxidation

A chemical reaction involving the loss of electrons or hydrogen atoms (OIL).

Reduction

A chemical reaction involving the gain of electrons or hydrogen atoms (RIG).

Adenosine triphosphate (ATP)

A molecule composed of an adenine base, a ribose sugar, and three phosphate groups, which stores energy in its phosphate bonds for cellular work.

Substrate-level phosphorylation

A mechanism of generating ATP where an enzyme directly transfers a phosphate group from a high-energy phosphorylated compound to ADP.

Oxidative phosphorylation

A mechanism of generating ATP that utilizes energy released from the oxidation of nutrients in an electron transport chain to create a proton gradient.

Photophosphorylation

A mechanism of generating ATP where light energy excites electrons in photosynthetic pigments, passing them through an electron transport chain to create a proton gradient.

Glycolysis

The metabolic process that oxidizes glucose into two molecules of pyruvic acid, producing a net yield of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Bridging step

The enzymatic conversion of 3-carbon pyruvic acid into 2-carbon Acetyl-CoA prior to the Krebs cycle, releasing $\text{CO}_2$ and producing $2\,\text{NADH}$ per glucose.

Krebs cycle

A metabolic pathway that completely oxidizes Acetyl-CoA, yielding $3\,\text{NADH}$, $1\,\text{FADH}_2$, $1\,\text{ATP}$, and $2\,\text{CO}_2$ per turn.

Electron transport chain (ETC)

A sequence of membrane-bound protein complexes (flavoproteins, metal-containing proteins, ubiquinones, cytochromes) that pass electrons through redox reactions to generate a proton gradient.

Chemiosmosis

The movement of protons down their electrochemical gradient across a membrane through ATP synthase to power the synthesis of ATP.

Aerobic respiration

Respiration in which molecular oxygen ($\text{O}_2$) acts as the final electron acceptor in the electron transport chain, generating the highest ATP yield.

Anaerobic respiration

Respiration in which an inorganic molecule other than oxygen (such as nitrate or sulfate) serves as the final electron acceptor in the electron transport chain.

Fermentation

An anaerobic process that uses an organic molecule as the final electron acceptor to re-oxidize NADH to $\text{NAD}^+$ without using the Krebs cycle or ETC.

Obligate aerobe

An organism, such as Mycobacterium tuberculosis, that requires oxygen to grow and colonize host tissue like the lungs.

Obligate anaerobe

An organism, such as Clostridium perfringens, that thrives in oxygen-deprived environments and causes deep tissue infections like gas gangrene.