Metabolism: Enzymes, Transport, and Catabolic Pathways

A set of Q&A flashcards covering enzymes, metabolism, transport mechanisms, major catabolic pathways, and their relevance to clinical microbiology.

What are enzymes?

Proteins that act as catalysts to speed up chemical reactions without being consumed in the reaction.

What is a coenzyme?

An organic molecule that aids enzyme function; vitamins can act as coenzymes (e.g., vitamin C, B12); NAD+ is a nonvitamin coenzyme.

What is a cofactor?

A metal ion (e.g., iron, copper, zinc) required by some enzymes, sometimes working with coenzymes.

What is the difference between constitutive and regulated enzymes?

Constitutive enzymes are produced continuously; regulated enzymes are produced only when needed.

What is competitive inhibition?

An inhibitor competes with the substrate for the enzyme's active site, reducing enzyme activity (e.g., clavulanate inhibits beta-lactamases to combat penicillin resistance).

What is noncompetitive inhibition?

An inhibitor binds to an allosteric site, changing enzyme shape and lowering activity regardless of substrate concentration.

What is phosphorylation?

Addition or removal of phosphate groups to regulate enzyme activity; kinases add phosphates, phosphatases remove.

What is posttranslational modification?

Chemical decorations (e.g., glycosylation) that alter enzyme activity after translation.

What is glycolysis?

Pathway that converts glucose to two pyruvate, yielding 2 ATP and 2 NADH per glucose.

What is NAD+/NADH?

Electron carrier; NAD+ accepts electrons to become NADH and must be recycled back to NAD+ to continue metabolism.

What is acetyl-CoA?

A two-carbon molecule formed from pyruvate that enters the Krebs cycle; also produced from fatty acid beta-oxidation.

What is the Krebs cycle (citric acid cycle)?

Pathway that processes acetyl-CoA, releases CO2, and generates ATP, NADH, and FADH2.

What is FAD/FADH2?

Electron carrier; FAD accepts electrons to become FADH2 and donates them to the electron transport chain.

What is the electron transport chain (ETC)?

Series of membrane-bound carriers that transfer electrons and pump protons to create a proton gradient.

What is the proton gradient and chemiosmosis?

A proton (H+) gradient across a membrane that drives ATP synthesis via ATP synthase (chemiosmosis).

What is ATP synthase?

Enzyme complex that uses proton flow to convert ADP and Pi into ATP.

What is cytochrome C oxidase?

Final ETC enzyme that transfers electrons to oxygen to form water, helping maintain the gradient.

What is the overall ATP yield of aerobic respiration per glucose?

Up to about 34 ATP per glucose (commonly cited as 30–32 due to shuttle costs).

What is fermentation?

Anaerobic process that converts pyruvate into other products to regenerate NAD+ (e.g., lactate, ethanol, CO2).

What are exoenzymes?

Enzymes secreted outside the cell that break down large polymers into smaller molecules for uptake.

What are endocytosis, pinocytosis, and phagocytosis?

Energy-dependent uptake processes in eukaryotes; endocytosis is general, pinocytosis ingests liquids, phagocytosis ingests large particles.

What is group translocation?

Active transport where the transported molecule is chemically modified during transport and trapped inside the cell.

Are transport pumps and channels specific?

Yes; most are highly specific for particular molecules or ions (e.g., glucose pumps, Na+ pumps).

What are catabolic vs anabolic processes?

Catabolism breaks down nutrients to release energy and building blocks; anabolism uses energy and building blocks to synthesize complex molecules.

What four catabolic pathways are highlighted in class?

Glycolysis, Krebs cycle, electron transport chain, and fermentation.

Why is metabolism clinically important?

Pathways are universal and underpin growth, infection, and drug targets; metabolic tests help identify microbes and guide chemotherapy development.

How can chemotherapy target metabolism while sparing host cells?

Some drugs target central microbial pathways (e.g., ATP synthase inhibitors like bedaquiline), but selective toxicity is challenging because pathogens and humans share many pathways.

How do sulfa drugs target bacteria?

They inhibit bacterial folate synthesis, a pathway humans obtain from diet, providing selective toxicity.

What is the central role of glucose in metabolism?

Glucose is a key energy source; its metabolism links energy production to biosynthesis and is a focal point in studying pathogens and host interactions.