Cellular Metabolism, Respiration, and Photosynthesis

Comprehensive vocabulary flashcards covering energy metabolism, cellular respiration, fermentation, alternative metabolic pathways, and photosynthesis as presented in the lecture notes.

Metabolism

The sum of all chemical reactions occurring in a cell or organism.

Metabolic Pathway

An ordered series of enzymatic reactions that transform substrates into products.

Catabolism

Metabolic process break down large molecules into smaller ones, releasing energy.

Anabolism

Metabolic processes that synthesize larger molecules from smaller building blocks, requiring energy.

Coupled Reaction

A pair of reactions in which an exergonic process drives an endergonic one through shared intermediates such as ATP or NADH.

ATP (Adenosine Triphosphate)

The primary energy currency of the cell; hydrolysis releases usable free energy.

Phosphoanhydride Bond

High-energy P–O bond in ATP whose hydrolysis drives cellular work.

Endergonic Reaction

A reaction that requires an input of free energy (ΔG > 0).

Exergonic Reaction

A reaction that releases free energy (ΔG < 0).

Hydrolysis of ATP

Exergonic cleavage of ATP to ADP (or AMP) and inorganic phosphate, releasing energy.

Oxidation

Loss of electrons, often accompanied by loss of hydrogen or gain of oxygen.

Reduction

Gain of electrons, by gain of hydrogen or loss of oxygen.

Redox Reaction

A chemical process in which oxidation and reduction occur simultaneously, transferring electrons and energy.

Electron Carrier

Molecule that temporarily stores energy by accepting electrons and hydrogen (e.g., NADH, FADH₂).

NAD⁺ (Nicotinamide Adenine Dinucleotide)

Oxidized electron carrier that accepts 2 e⁻ and 1 H⁺ to form NADH.

NADH

Reduced form of NAD⁺; holds high-energy electrons used to generate ATP.

FAD/FADH₂

Flavin adenine dinucleotide (oxidized) and its reduced form; another electron carrier feeding the ETC.

NADP⁺/NADPH

Electron carrier pair primarily used in anabolic pathways and photosynthesis.

Cellular Respiration

Metabolic pathway that breaks down glucose to CO₂ and H₂O while capturing energy as ATP, NADH, and FADH₂.

Glycolysis

Anaerobic pathway in the cytosol converting glucose to pyruvate, producing 2 ATP and 2 NADH. (break down of glucose)

Pyruvate Oxidation

Mitochondrial reaction converting pyruvate to acetyl-CoA, generating CO₂ and NADH.

Citric Acid Cycle (Krebs Cycle)

Series of mitochondrial matrix reactions oxidizing acetyl-CoA to CO₂ while producing NADH, FADH₂, and GTP/ATP.

Oxidative Phosphorylation

Process in which the electron transport chain and chemiosmosis synthesize the majority of cellular ATP.

Electron Transport Chain (ETC)

Inner-mitochondrial-membrane complexes that pass electrons from NADH/FADH₂ to O₂, pumping protons.

Chemiosmosis

Use of a proton gradient to drive ATP synthesis via ATP synthase.

ATP Synthase

Rotary enzyme that couples proton flow to phosphorylation of ADP to ATP.

Coenzyme A

Carrier of acyl groups; forms acetyl-CoA after pyruvate oxidation.

Acetyl-CoA

Two-carbon donor that enters the citric acid cycle.

Proton Gradient

Electrochemical difference in H⁺ concentration across a membrane, storing potential energy.

Role of Oxygen in ETC

Terminal electron acceptor that combines with electrons and H⁺ to form water.

Fermentation

Anaerobic pathway that reoxidizes NADH to NAD⁺, allowing glycolysis to continue.

Lactic Acid Fermentation

Conversion of pyruvate to lactate, regenerating NAD⁺ in animal cells and some microbes.

Alcohol Fermentation

Yeast pathway reducing acetaldehyde to ethanol, regenerating NAD⁺.

Anaerobic Respiration

Respiration using an ETC with a final electron acceptor other than oxygen.

β-Oxidation

Process that breaks fatty acids into acetyl-CoA units for entry into the citric acid cycle.

Deamination

Removal of amino groups from amino acids before their carbon skeletons enter respiration.

Autotroph

Organism that produces its own organic molecules using energy from light or chemicals.

Heterotroph

Organism that obtains energy and carbon by consuming other organisms.

Photosynthesis

Process converting light energy, CO₂, and H₂O into organic molecules and O₂.

Light Reactions

Photosynthetic steps that convert light energy into ATP and NADPH in thylakoid membranes.

Carbon Fixation Reactions (Calvin Cycle)

Stromal reactions using ATP, NADPH, and CO₂ to synthesize carbohydrates.

Pigment

Molecule that absorbs specific wavelengths of light; e.g., chlorophylls and carotenoids.

Chlorophyll

Primary green pigment absorbing red and blue light, driving photosynthesis.

Carotenoid

Accessory pigment (e.g., β-carotene) that absorbs blue/green light and protects against photo-damage.

Photon

Discrete packet of light energy whose amount depends on wavelength.

Z-Scheme

Model describing the linear flow of electrons from water through Photosystem II and I to NADP⁺, forming ATP and NADPH.

Cyclic Electron Flow

Photosynthetic route that cycles electrons around Photosystem I to generate extra ATP without NADPH production.

Photophosphorylation

ATP formation driven by the proton motive force generated during the light reactions.

Calvin Cycle

Three-phase pathway (carbon fixation, reduction, regeneration) producing G3P from CO₂.

RuBP (Ribulose-1,5-Bisphosphate)

5-carbon CO₂ acceptor molecule regenerated in the Calvin cycle.

3-Phosphoglycerate (3PG)

First stable product of CO₂ fixation by RuBP carboxylation.

Glyceraldehyde-3-Phosphate (G3P)

3-carbon sugar formed in the Calvin cycle; precursor to glucose and other carbohydrates.

Gluconeogenesis

Anabolic pathway synthesizing glucose from non-carbohydrate precursors such as pyruvate; costs 6 ATP.

Essential Nutrient

Molecule an organism cannot synthesize and must obtain from its environment.

Chemosynthesis

Process by which some autotrophs use energy from inorganic chemical reactions to make organic molecules.

CO₂ Fixation

Incorporation of inorganic CO₂ into organic molecules, primarily via the Calvin cycle.