2.4.Energy transformation

A comprehensive set of vocabulary flashcards covering key terms from cellular respiration and photosynthesis, including metabolism pathways, energy transformations, enzymes, ATP production, and chloroplast-based processes.

Autotrophs

Organisms that can make their own food from inorganic materials and energy (producers).

Heterotrophs

Organisms that obtain energy by consuming other organisms or their food (consumers).

Catabolic pathway

A metabolic pathway that breaks down molecules into smaller units, releasing energy.

Anabolic pathway

A metabolic pathway that builds larger molecules from smaller building blocks, consuming energy.

Endergonic reaction

A reaction that requires a net input of energy; products have higher energy than reactants.

Exergonic reaction

A reaction that releases energy; products have lower energy than reactants.

ΔG (Gibbs free energy)

The change in free energy of a system; determines whether a reaction is endergonic or exergonic.

Enzyme

A protein (or RNA in some cases) that acts as a catalyst to increase reaction rate by lowering activation energy.

Activation energy

Energy required to start a reaction.

Cofactors

Inorganic ions or nonprotein molecules that assist enzymes in catalysis.

Coenzymes

Organic molecules (often derived from vitamins) that help enzymes perform reactions.

Competitive inhibitor

A molecule that blocks substrate binding by occupying the enzyme's active site.

Non-competitive inhibitor

An inhibitor that binds elsewhere on the enzyme, changing its shape and reducing activity.

Allosteric site

A site on an enzyme other than the active site where regulators bind to alter activity.

ATP

Adenosine triphosphate, the cell’s main energy currency; composed of ribose, adenine, and three phosphate groups.

ADP

Adenosine diphosphate, produced when ATP is hydrolyzed; can be rephosphorylated to ATP.

Substrate-level phosphorylation

Direct transfer of a phosphate group from a substrate to ADP to form ATP.

Oxidative phosphorylation

ATP synthesis powered by a proton gradient across the inner mitochondrial membrane via ATP synthase.

Glycolysis

Glucose -> 2 pyruvate in the cytoplasm; net gain of 2 ATP and 2 NADH per glucose.

Pyruvate oxidation

Pyruvate is converted to Acetyl-CoA in the mitochondrial matrix, producing NADH and CO2.

Acetyl-CoA

Two-carbon acetyl group linked to CoA; enters the Krebs cycle after pyruvate oxidation.

Krebs cycle (Citric Acid Cycle)

Mitochondrial matrix cycle producing ATP (or GTP), CO2, NADH, and FADH2; oxaloacetate is regenerated.

NADH

Reduced electron carrier that delivers electrons to the electron transport chain; generated in glycolysis, pyruvate oxidation, and Krebs cycle.

FADH2

Electron carrier produced in the Krebs cycle that donates electrons to the electron transport chain via Complex II.

Electron transport chain (ETC)

A series of protein complexes in the inner mitochondrial membrane that transfer electrons to O2 and pump protons.

Chemiosmosis

Movement of protons back into the mitochondrial matrix through ATP synthase to generate ATP.

Cyanide

Inhibitor of Complex IV of the ETC, blocking aerobic ATP production.

Anaerobic respiration

Respiration without oxygen using inorganic molecules as the final electron acceptor (e.g., sulfate-reducing bacteria).

Fermentation

Anaerobic process that regenerates NAD+ by producing lactate or ethanol; incomplete glucose oxidation.

Lactic acid fermentation

Pyruvate is reduced to lactate; occurs in animal muscles and some bacteria.

Ethanol fermentation

Pyruvate is converted to ethanol and CO2; occurs in yeast and some bacteria.

Warburg effect

Metabolic shift in cancer cells toward glycolysis and lactate production even in the presence of oxygen.

Pentose phosphate pathway (PPP)

Glucose pathway that generates NADPH and ribose-5-phosphate for nucleotide and lipid biosynthesis.

Photosynthesis

Process that converts light energy into chemical energy, producing glucose from CO2 and water; oxygen is released.

Light-dependent reactions

Photosynthesis stage that captures light to make ATP and NADPH; occurs in the thylakoid membranes.

Calvin cycle (light-independent reactions)

Photosynthesis stage that uses ATP and NADPH to synthesize organic molecules from CO2 in the stroma.

Chloroplast

Organelle where photosynthesis takes place in plants and algae.

Thylakoid membrane

Internal membrane system in chloroplasts housing the photosystems and ETC.

Grana

Stacks of flattened thylakoids within the chloroplast.

Stroma

Fluid surrounding thylakoids where the Calvin cycle occurs.

Stroma lamella

Connective thin membranes linking grana in the chloroplast.

Pigments

Molecules that absorb light energy; in photosynthesis, chlorophylls and carotenoids are key pigments.

Chlorophyll a

Main pigment that directly converts light energy to chemical energy in photosynthesis.

Chlorophyll b

Accessory pigment that expands the range of light wavelengths absorbed.

Carotenoids

Accessory pigments that absorb light energy and protect chlorophyll from damage.

Photosystem II (PSII)

Photosystem that absorbs light and uses the energy to split water and pump protons into the thylakoid lumen.

Water-splitting enzyme

Enzyme in PSII that splits water to release O2, protons, and electrons.

Photosystem I (PSI)

Photosystem that absorbs light and transfers electrons to NADP+ to form NADPH.

NADP+ reductase

Enzyme that transfers electrons to NADP+, forming NADPH in the light reactions.

NADPH

Reduced electron carrier used in the Calvin cycle to reduce CO2 into sugars.

ATP synthase (in chloroplasts)

Enzyme that uses the proton gradient to synthesize ATP from ADP and Pi during photosynthesis.

RuBP (ribulose-1,5-bisphosphate)

Five-carbon sugar that accepts CO2 at the start of the Calvin cycle.

G3P (glyceraldehyde-3-phosphate)

Three-carbon sugar produced in the Calvin cycle; a precursor for glucose and other carbohydrates.