Cellular Respiration, Photosynthesis, Energy, and Metabolism

Vocabulary practice flashcards covering cell respiration, photosynthesis, thermodynamics, enzyme kinetics, and ATP metabolism.

Energy

The ability to do work, required as an input for cellular processes.

Kinetic Energy

The energy of motion.

Potential Energy

Stored energy or the potential of an object to perform work.

Chemical Energy

A form of potential energy that is stored within the chemical bonds between atoms.

Chemical Work

A type of cellular work that involves making larger molecules from smaller ones.

Transport Work

A type of cellular work involving moving materials, including the uptake and removal of nutrients, elimination of waste, and maintenance of concentration gradients.

Mechanical Work

A type of cellular work involving physical movement, such as the movement of whole organisms, cells in multicellular organisms, or organelles within cells.

First Law of Thermodynamics

The principle stating that energy cannot be created nor destroyed, only transformed into different forms or moved between a system and its surroundings.

Second Law of Thermodynamics

The principle stating that energy transfer is not $100\%$ efficient and involves some loss of energy from the system in an unusable form (usually as heat), increasing entropy.

Entropy ($S$)

The amount of randomness or disorder within a system; natural systems spontaneously tend toward disorder unless energy is spent to maintain order.

Gibbs Free Energy ($G$)

The amount of energy available for work after subtracting energy lost as heat or other unusable forms, represented by the equation $\Delta G = \Delta H - T\Delta S$.

Enthalpy ($H$)

The total energy content of a system, reactant, or product.

Exergonic Reaction

A spontaneous chemical reaction where products have less free energy than reactants ($-\Delta G$), releasing energy and increasing the system's entropy.

Endergonic Reaction

A non-spontaneous chemical reaction where products have more free energy than reactants ($+\Delta G$), requiring an input of energy and decreasing system entropy.

Activation Energy

The minimum energy input required to destabilize existing chemical bonds and break them to initiate a reaction.

Catalyst

A substance that speeds up a reaction by lowering its activation energy through stabilizing the transition state, without altering $\Delta G$ or being consumed.

Enzyme

A biological catalyst, typically a protein (or RNA), possessing a unique three-dimensional conformation that facilitates specific biochemical reactions.

Active Site

The specific region of an enzyme where substrate molecules bind and undergo catalysis.

Induced Fit

The conformational change an enzyme undergoes upon substrate binding to ensure a snug fit that aids in catalysis.

Competitive Inhibition

A mechanism of enzyme inhibition where an inhibitor binds directly to the active site, physically preventing substrate binding.

Allosteric Regulation

The modification of enzyme activity through the binding of an effector molecule to an allosteric site separate from the active site, altering the enzyme's shape to either activate or inhibit it.

Feedback Inhibition

A cellular control mechanism in which the high concentration of an end product of a metabolic pathway inhibits an enzyme operating early in that pathway.

Metabolism

The totality of all chemical reactions that occur inside a living cell.

Biochemical Pathway

A sequence of consecutive chemical reactions in which the product of one reaction becomes the reactant for the next.

Anabolic Pathway

A metabolic pathway that consumes net energy (endergonic) to build complex, large molecules from simpler building blocks.

Catabolic Pathway

A metabolic pathway that breaks down complex, large molecules into simpler ones, resulting in a net release of energy (exergonic).

ATP (Adenosine Triphosphate)

The universal energy currency of cells; a nucleotide comprised of the nitrogenous base adenine, a ribose pentose sugar, and three phosphate groups.

Substrate-Level Phosphorylation

The direct synthesis of ATP accomplished when an enzyme transfers a phosphate group from a phosphorylated substrate directly to ADP; occurs during glycolysis and the Citric Acid Cycle.

Oxidative Phosphorylation

The process of generating ATP via ATP synthase driven by a proton gradient (chemiosmosis) across the inner mitochondrial or thylakoid membrane.

Oxidation

The loss of one or more electrons by a chemical substance.

Reduction

The gain of one or more electrons by a chemical substance.

Glycolysis

An anaerobic metabolic pathway in the cytoplasm that oxidizes 1 glucose molecule into 2 pyruvate molecules, yielding a net of 2 ATP and 2 NADH.

Pyruvate Oxidation

The oxidation of 2 pyruvate molecules in the mitochondrial matrix to generate 2 acetyl-CoA, 2 NADH, and 2 $CO_2$.

Citric Acid Cycle

A cyclic series of reactions in the mitochondrial matrix where acetyl-CoA joins oxaloacetate to form citrate, ultimately yielding 2 ATP, 6 NADH, 2 $FADH_2$, and 4 $CO_2$ per glucose molecule.

Chemiosmosis

The diffusion of protons ($H^+$) down an electrochemical gradient across a membrane through ATP synthase to synthesize ATP from ADP and inorganic phosphate ($P_i$).

Aerobic Respiration

Respiration utilizing oxygen ($O_2$) as the final electron acceptor in the electron transport chain, involving glycolysis, the citric acid cycle, and oxidative phosphorylation.

Anaerobic Respiration

Respiration utilizing an inorganic molecule other than oxygen (e.g., sulfur, nitrate, $CO_2$) as the final electron acceptor in the ETC; produces less energy than aerobic respiration.

Fermentation

An anaerobic process relying solely on glycolysis, wherein electrons from NADH are transferred to organic molecules to regenerate $NAD^+$ while generating minimal ATP.

Photon

The smallest discrete packet of light energy, with an energy quantity inversely proportional to its wavelength.

Chlorophyll

The primary photosynthetic pigment that absorbs blue and red wavelengths of light and reflects green wavelengths.

Carotenoids

Accessory photosynthetic pigments that absorb blue and green wavelengths of light and reflect red and orange light.

Antenna Complex

An assembly of accessory pigment molecules that captures photons and transfers excitation energy (without transferring electrons) to the reaction center.

Reaction Center

A complex of transmembrane proteins containing chlorophyll $a$ molecules that absorbs energy from the antenna complex to excite and transfer electrons to the primary electron acceptor.

Photosystem II (PSII)

A photosystem embedded in the thylakoid membrane that absorbs light, energizes electrons, and replenishes lost electrons via the oxidation of water into $O_2$ and $H^+$ protons.

Photosystem I (PSI)

A photosystem in the thylakoid membrane that absorbs light to energize electrons destined to reduce $NADP^+$ into NADPH; its electrons are replenished from PSII via an electron transport chain.

Calvin Cycle

The light-independent phase of photosynthesis occurring in the stroma, using ATP and NADPH from light reactions to fix carbon into glyceraldehyde 3-phosphate (G3P).

Carbon Fixation

The initial stage of the Calvin Cycle where 6 molecules of $CO_2$ are attached to 6 molecules of ribulose 1,5-bisphosphate (RuBP) to yield 12 molecules of 3-phosphoglycerate (3PG).