Cell Metabolism, Respiration, and Photosynthesis Vocabulary Flashcards

Comprehensive vocabulary flashcards generated directly from the Cell Metabolism lecture notes, covering energy transformations, thermodynamics, enzyme kinetics, respiration stages, and photosynthesis.

Kinetic Energy

The energy of movement, which includes thermal, sound, and electromagnetic energy.

Potential Energy

Stored energy, which includes gravitational, elastic, chemical-bond, and nuclear energy.

First Law of Thermodynamics

The law stating that energy cannot be created or destroyed; it can be transformed, and total energy is always conserved.

Second Law of Thermodynamics

The law stating that the entropy (measure of disorder or how spread out energy is) of the entire universe will always increase over time.

Entropy

A measure of disorder or how spread out energy is within a system.

Endergonic Reaction

A chemical reaction that requires an input of free energy ($\Delta G > 0$) because the products have higher free energy than the reactants.

Exergonic Reaction

A chemical reaction that releases free energy ($ΔG < 0$) because the products have lower free energy than the reactants.

Hydrolysis

A chemical reaction in which a molecule interacts with water, causing a chemical bond within the molecule to break.

Condensation Reaction

A chemical reaction in which two molecules combine to form a larger molecule, producing water as a by-product.

Activation Energy ($E_a$)

The initial amount of energy required to initiate a chemical reaction.

Ribozymes

RNA molecules that function as biological catalysts to increase reaction rates.

Substrate

A specific reactant molecule that binds to the active site of an enzyme.

Induced Fit

The change in shape that an enzyme undergoes when a substrate binds to its active site to maximize binding tightness.

Metabolic Pathway

A coordinated series of chemical reactions that convert precursor molecules into different target molecules, with each step catalyzed by specific enzymes.

ATP (Adenosine Triphosphate)

The primary cellular energy currency composed of adenine, ribose sugar, and three phosphate groups, releasing approximately $-30\,kJ/mol$ of free energy upon hydrolysis.

Reduction

The gain of one or more electrons (or hydrogen atoms) by an atom or molecule.

Oxidation

The loss of one or more electrons (or hydrogen atoms) from an atom or molecule.

NADH

The reduced form of the coenzyme nicotinamide adenine dinucleotide ($\text{NAD}^+$), functioning as an electron carrier whose reoxidation yields $-219\,kJ/mol$ of free energy.

Cellular Respiration

A series of metabolic reactions used by cells to harvest energy from molecules by oxidizing $\text{C–C}$ and $\text{C–H}$ bonds to $\text{CO}_2$ in the presence of oxygen.

Glycolysis

The 10-reaction cytosolic stage of cellular respiration that oxidizes one 6-carbon glucose molecule into two 3-carbon pyruvate molecules, yielding a net $2\,ATP$ and $2\,NADH$.

Pyruvate Oxidation

The mitochondrial stage of cellular respiration that converts pyruvate into acetyl-CoA, producing one $NADH$ and releasing one $\text{CO}_2$ per pyruvate.

Citric Acid Cycle

An 8-reaction cyclic mitochondrial pathway that fully oxidizes acetyl-CoA to $\text{CO}_2$, producing $3\,NADH$, $1\,FADH_2$, and $1\,GTP$ per turn.

Electron Transport Chain

A set of four protein complexes embedded in the inner mitochondrial membrane that pass electrons from $NADH$ and $FADH_2$ to oxygen while pumping protons to establish a gradient.

Proton-Motive Force

The potential energy stored in the concentration and charge gradient of protons ($\text{H}^+$) established across a membrane.

Chemiosmosis

The movement of ions across a semipermeable membrane down their electrochemical gradient, used by ATP synthase to drive the formation of ATP.

ATP Synthase

A conserved multi-subunit protein complex consisting of a transmembrane $F_o$ proton channel and a catalytic $F_1$ unit that synthesizes ATP from ADP and inorganic phosphate.

Uncoupling Protein 1 (UCP1)

A transmembrane channel protein present in brown fat cell mitochondria that dissipates the proton gradient by allowing protons to flow without generating ATP, producing heat instead.

Competitive Inhibitors

Molecules structurally similar to the substrate that non-covalently and reversibly bind to the active site of an enzyme, preventing substrate binding.

Allosteric Regulation

A non-covalent binding of a regulatory molecule (activator or inhibitor) to a site distinct from the active site, inducing a conformational change that alters enzyme activity.

Catabolism

Metabolic reactions that break down complex molecules into simpler ones, often releasing energy that can be captured as ATP.

Anabolism

Metabolic reactions that synthesize complex cellular molecules from simpler precursors, requiring an input of energy.

Light Reactions

The initial phase of photosynthesis occurring in the thylakoid membrane, where solar energy absorbed by pigments is converted into chemical energy stored in ATP and NADPH.

Carbon Fixation Reactions (Calvin Cycle)

The dark reactions of photosynthesis occurring in the stroma of chloroplasts that use ATP and NADPH to convert $\text{CO}_2$ into glyceraldehyde-3-phosphate (G3P) and sugars.

Chloroplast

A specialized plant cell organelle bounded by inner and outer membranes, containing thylakoids arranged in grana stacks suspended in fluid stroma.

Thylakoid

Flattened membrane sacs inside chloroplasts that contain light-harvesting complexes, electron transport chains, and ATP synthase for the light reactions of photosynthesis.

Stroma

The fluid-filled region surrounding the grana inside the inner membrane of a chloroplast where carbon fixation reactions take place.

Rubisco

The primary enzyme that catalyzes carbon fixation by joining $\text{CO}_2$ to ribulose 1,5-bisphosphate (RuBP) at the start of the Calvin cycle.

Kinetic Energy

The energy of movement, which includes thermal, sound, and electromagnetic energy.

Potential Energy

Stored energy, which includes gravitational, elastic, chemical-bond, and nuclear energy.

First Law of Thermodynamics

The law stating that energy cannot be created or destroyed; it can only be transformed and is always conserved.

Second Law of Thermodynamics

The law stating that the entropy (disorder) of the universe always increases over time, causing usable energy to decrease after transformations.

Entropy

A measure of disorder or how spread out energy is across a system or universe.

Endergonic Reaction

A chemical reaction that consumes free energy ($\text{positive } \tan(\theta)$ or $\tan(x)$ or $\text{change } \text{in } \text{free } \text{energy } \text{is positive}$ / $\text{requires } \text{energy}$).

Exergonic Reaction

A chemical reaction that releases free energy.

Hydrolysis

A reaction in which a molecule interacts with water and a bond within the molecule is broken.

Condensation

A reaction in which two molecules combine to form a larger molecule, producing water as a by-product.

Activation Energy ($E_a$)

The minimum energy barrier required to initiate a chemical reaction.

Enzyme

A biological catalyst (mostly proteins, some RNA) that increases reaction rates by lowering activation energy without being permanently altered.

Ribozymes

RNA molecules that function as biological catalysts.

Substrates

Reactant molecules that specifically bind to the active site of an enzyme.

Active Site

The specific site on an enzyme where reactant substrates bind and undergo a chemical reaction.

Induced Fit

The change in shape of an enzyme upon binding its substrate to ensure a tight interaction, analogous to a baseball in a catcher's mitt.

Metabolic Pathway

A coordinated series of chemical reactions that convert starting molecules into different molecules, each reaction catalyzed by a specific enzyme.

Reduction

The gain of one or more electrons (or hydrogen atoms) by an atom or molecule.

Oxidation

The loss of one or more electrons (or hydrogen atoms) from an atom or molecule.

$\text{NAD}^+$ / $\text{NADH}$

Nicotinamide adenine dinucleotide, a coenzyme electron carrier in redox reactions that exists in an oxidized form ($\text{NAD}^+$) and a reduced form ($\text{NADH}$).

Cellular Respiration

Metabolic reactions used by cells to harvest energy from organic molecules by oxidizing C-C and C-H bonds to $\text{CO}_2$ in the presence of oxygen.

Glycolysis

The initial 10-step process of cellular respiration in the cytosol that splits 1 glucose molecule into 2 pyruvates, yielding 2 net ATP and 2 $\text{NADH}$.

Substrate-Level Phosphorylation

The direct synthesis of ATP by transferring a phosphate group from a phosphorylated metabolic intermediate to ADP.

Pyruvate Oxidation

The stage of respiration in mitochondria where pyruvate is oxidized to acetyl-CoA, releasing 1 $\text{CO}_2$ and producing 1 $\text{NADH}$ per pyruvate.

Citric Acid Cycle

An 8-reaction cycle in the mitochondrial matrix that fully oxidizes acetyl-CoA to $\text{CO}_2$, producing 3 $\text{NADH}$, 1 $\text{FADH}_2$, and 1 GTP per turn.

Proton-Motive Force

The potential energy stored in an electrochemical gradient created by pumping protons across the inner mitochondrial membrane into the intermembrane space.

ATP Synthase

A protein complex consisting of $F_o$ and $F_1$ units that converts the potential energy of a proton gradient into chemical energy stored in ATP.

Chemiosmosis

The movement of ions across a semipermeable barrier down their electrochemical gradient, used by ATP synthase to drive ATP synthesis.

Uncoupling Protein 1 (UCP1)

A transmembrane channel protein in brown fat cells that allows protons to cross the inner mitochondrial membrane without generating ATP, producing heat instead.

Fermentation

An anaerobic metabolic process that breaks down glucose and regenerates $\text{NAD}^+$ from $\text{NADH}$ to keep glycolysis running when oxygen is absent.

Competitive Inhibitor

A non-covalent, reversible regulatory molecule similar in structure to the substrate that binds to an enzyme's active site and prevents substrate binding.

Allosteric Regulation

Regulation of enzyme activity caused by non-covalent binding of an activator or inhibitor at a regulatory site distinct from the active site.

Catabolism

The metabolic breakdown of complex molecules into simpler ones, usually accompanied by energy release.

Anabolism

The metabolic synthesis of complex molecules from simpler precursors, requiring an input of energy.

Chloroplast

A plant organelle bounded by double membranes and containing thylakoids and stroma, responsible for carrying out photosynthesis.

Thylakoid

A flattened sac of membrane within a chloroplast that houses pigments and proteins for the light reactions of photosynthesis.

Stroma

The fluid-filled space between the inner chloroplast membrane and grana where carbon fixation reactions occur.

Chlorophyll a

A primary photosynthetic pigment that absorbs blue and red light while reflecting green and yellow light.

Chlorophyll b

An accessory photosynthetic pigment that absorbs bluish-green and reddish-orange light while reflecting green and yellow light.

$\beta$-Carotene

An accessory pigment in plant leaves that absorbs light in the blue-green range and reflects yellow and orange light.

Light Reactions

The first phase of photosynthesis occurring in thylakoid membranes that converts photon energy into chemical energy stored in ATP and NADPH while splitting water to release $\text{O}_2$.

Carbon Fixation Reactions

The second phase of photosynthesis occurring in the stroma (Calvin cycle) that utilizes ATP and NADPH from light reactions to convert $\text{CO}_2$ into sugars.

Rubisco

The primary enzyme that catalyzes the initial carbon fixation reaction joining $\text{CO}_2$ to RuBP in the Calvin cycle.