Cellular Respiration, Fermentation, and Photosynthesis

Vocabulary practice flashcards covering cellular respiration, fermentation, and photosynthesis lectures, including energy pathways, organelle structures, enzyme mechanisms, and key chemical intermediates.

Photosynthesis

The endergonic biological process that uses sunlight to convert energy in $C=O$ bonds into $C-H$ and $C-C$ bonds of carbohydrates, reducing $CO_2$ and consuming $H_2O$ while releasing $O_2$ as a by-product.

Chloroplast

A double-membrane organelle found in green plants, algae, and photosynthetic eukaryotes that serves as the site of photosynthesis.

Thylakoid

A flattened, sac-like membrane structure within chloroplasts that contains photosynthetic pigments and the molecular machinery required to convert light into ATP and NADPH.

Granum

A stack of thylakoid membranes within the chloroplast (plural: grana).

Stroma

The fluid-filled space between the thylakoids and the chloroplast inner membrane where the light-independent reactions (Calvin cycle) take place.

Photon

A discrete, particle-like packet of electromagnetic energy characterized by a specific wavelength.

Pigment

A molecule that absorbs only specific wavelengths of visible light and reflects or transmits the unabsorbed wavelengths.

Chlorophyll

The primary photosynthetic pigment class ($a$ and $b$) possessing a light-absorbing porphyrin ring head with a magnesium ($Mg$) atom and a hydrophobic isoprene tail that anchors it in the thylakoid membrane.

Carotenoid

An accessory pigment that absorbs blue and green wavelengths, transmits yellow, orange, and red light, broadens the spectrum of light usable for photosynthesis, and protects chlorophylls by stabilizing free radicals.

Fluorescence

A mechanism of dissipating light energy wherein an excited electron drops directly back down to its ground state, releasing energy as heat and a photon of lower energy light.

Resonance Energy Transfer

The process by which energy from an excited electron in an antenna pigment is transferred to an adjacent pigment molecule until it reaches the reaction center.

Antenna Complex

A cluster of chlorophylls and accessory pigments within a photosystem that gathers light energy and funnels it via resonance toward the central reaction center.

Reaction Center

A specialized protein-pigment complex containing a 'special pair' of chlorophyll $a$ molecules where electromagnetic energy is transformed into chemical energy via redox electron transfer to a primary electron acceptor.

Photosystem II

The photosynthetic complex that absorbs light, splits water into protons ($H^+$) and $O_2$, and transfers high-energy electrons through pheophytin to an electron transport chain to generate a proton gradient for ATP synthesis.

Pheophytin

The initial electron acceptor in Photosystem II that accepts electrons directly from the excited reaction center chlorophyll.

Photosystem I

The photosynthetic complex that receives electrons from the Photosystem II transport chain, re-excites them with light, and transfers them via ferredoxin to $NADP^+$ reductase to form NADPH.

Photophosphorylation

The production of ATP in chloroplasts driven by the proton-motive force generated across the thylakoid membrane by light-dependent electron transport.

Enhancement Effect

The phenomenon where the rate of photosynthesis increases dramatically when photosynthetic cells are simultaneously exposed to both red and far-red wavelengths of light.

Calvin Cycle

The light-independent metabolic pathway in the chloroplast stroma that consumes ATP and NADPH to convert $CO_2$ into the 3-carbon sugar glyceraldehyde-3-phosphate (G3P).

Rubisco

The carbon-fixing enzyme in the chloroplast stroma that catalyzes the initial addition of $CO_2$ to ribulose 1,5-bisphosphate (RuBP).

Ribulose 1,5-bisphosphate (RuBP)

A 5-carbon sugar molecule that acts as the initial $CO_2$ acceptor in the carbon fixation stage of the Calvin cycle and is regenerated in the cycle's final phase.

Glyceraldehyde-3-phosphate (G3P)

A 3-carbon phosphorylated carbohydrate produced by the Calvin cycle that serves as the immediate precursor for synthesis of glucose, sucrose, and starch.

Adenosine Triphosphate (ATP)

The primary energy currency of the cell, composed of adenine, ribose, and three phosphate groups linked by high-energy bonds whose hydrolysis releases usable cellular energy.

Autotroph

An organism that synthesizes complex organic compounds such as glucose from inorganic carbon ($CO_2$) using energy from sunlight (photoautotroph) or inorganic chemical oxidation (chemoautotroph).

Heterotroph

An organism that obtains carbon and energy by ingesting preformed organic molecules produced by other living or decaying organisms.

Nicotinamide Adenine Dinucleotide ($NAD^+$)

A vital coenzyme and mobile electron carrier that accepts two electrons and one proton (a hydride ion, $H^-$) during catabolic oxidation reactions, reducing to NADH.

Substrate-Level Phosphorylation

The production of ATP through the direct, enzyme-catalyzed transfer of a phosphate group from a phosphorylated organic substrate directly to ADP.

Oxidative Phosphorylation

The synthesis of ATP driven by energy released through sequential electron transfers in an electron transport chain to oxygen, generating a proton gradient that operates ATP synthase.

Glycolysis

A ten-step metabolic sequence taking place in the cytosol that oxidizes one 6-carbon glucose molecule into two 3-carbon pyruvates, yielding a net of $2\text{ ATP}$ and $2\text{ NADH}$ without requiring oxygen.

Pyruvate Processing

The oxidative decarboxylation of pyruvate catalyzed by pyruvate dehydrogenase in the mitochondrial matrix, converting each pyruvate into one acetyl CoA, one $CO_2$, and one NADH.

Citric Acid Cycle

A cyclic eight-step metabolic pathway in the mitochondrial matrix that oxidizes acetyl groups from acetyl CoA to $CO_2$, generating $3\text{ NADH}$, $1\text{ FADH}_2$, and $1\text{ ATP}$ per turn ($6\text{ NADH}$, $2\text{ FADH}_2$, $2\text{ ATP}$, and $4\text{ }CO_2$ per glucose).

Electron Transport Chain (ETC)

A series of membrane-bound multiprotein complexes and mobile carriers located in the inner mitochondrial membrane (or cristae) that transfer electrons from NADH and $FADH_2$ to $O_2$ while pumping protons into the intermembrane space.

Chemiosmotic Hypothesis

The model proposing that the connection between electron transport and ATP synthesis is indirect; electron transport pumps protons to establish an electrochemical gradient that drives ATP synthase.

Proton-Motive Force

The potential energy stored in an electrochemical gradient of protons ($H^+$) across an inner mitochondrial or thylakoid membrane.

ATP Synthase

A multiprotein complex comprised of a membrane-spanning proton channel ($F_0$ unit) and a catalytic matrix knob ($F_1$ unit) connected by a central stalk that rotates to phosphorylate ADP to ATP.

Phosphofructokinase (PFK)

A key regulatory allosteric enzyme catalyzing the committed step of glycolysis (phosphorylation of fructose 6-phosphate), inhibited by high levels of ATP and activated by ADP.

Beta-Oxidation

The catabolic pathway that breaks down fatty acid chains into 2-carbon acetyl CoA molecules that can enter the citric acid cycle directly.

Deamination

The enzymatic removal of the amino group from an amino acid, allowing the remaining carbon skeleton to enter respiratory pathways as pyruvate, acetyl groups, or citric acid cycle intermediates.

Fermentation

An anaerobic metabolic pathway that regenerates $NAD^+$ by transferring electrons from NADH to pyruvate or its derivatives, allowing glycolysis to continue producing $2\text{ ATP}$ per glucose in the absence of oxygen.

Lactic Acid Fermentation

An anaerobic pathway occurring in animal muscle cells and certain bacteria where pyruvate directly accepts electrons from NADH to form lactate, regenerating $NAD^+$ without producing $CO_2$.

Alcohol Fermentation

An anaerobic pathway occurring in yeast where pyruvate is enzymatically converted to acetaldehyde and $CO_2$, and acetaldehyde is subsequently reduced by NADH to produce ethanol and regenerate $NAD^+$.

Catabolic Pathway

A metabolic pathway involving the breakdown of complex fuel molecules into smaller units, accompanied by the release of energy and synthesis of ATP.

Anabolic Pathway

A biosynthetic metabolic pathway that utilizes chemical energy (ATP) and intermediate metabolites to assemble macromolecules such as proteins, nucleic acids, and lipids.

Hypoxia

A condition of severely depleted oxygen levels in aquatic environments or living tissues that halts electron transport and forces cells into anaerobic fermentation.