Cell Biology: Bioenergetics, Membranes, and Transport Review

Vocabulary practice flashcards covering cell biology topics including cellular respiration, membrane structure, enzyme kinetics, bioenergetics, and transport mechanisms across Lectures 6 through 9.

Amphibolic Pathway

A metabolic pathway that functions in both breaking down molecules (catabolism) and building up macromolecules (anabolism), exemplified by the citric acid cycle.

Glycolysis

The metabolic pathway occurring floating freely in the cytoplasm that breaks down a six-carbon glucose molecule into two molecules of pyruvate.

Reduction

The addition of electrons (or hydrogenation) to a molecule, which reduces its chemical charge and transfers energy to it.

Oxidation

The removal of electrons (or dehydrogenation) from a molecule, which releases energy and leaves the carrier in an uncharged state.

Fluid Mosaic Model

A model of biological membranes where lipids represent the fluid component controlling fluidity, and proteins represent the mosaic component embedded within the bilayer.

FRAP (Fluorescence Recovery After Photobleaching)

An experimental technique used to determine whether lipids and proteins within a cell membrane are capable of lateral movement.

Unsaturated Fatty Acids

Fatty acids containing one or more double bonds that create kinks/bends in the hydrocarbon chains, effectively increasing membrane fluidity.

Steroid Structure

A class of membrane lipids recognized structurally by a characteristic four-ring arrangement described as "three rooms and a garage."

Glycoproteins

Membrane proteins attached to carbohydrate chains that project toward the extracellular space to facilitate cell-cell recognition.

Simple Diffusion

The unaided passive movement of small or nonpolar solutes directly across the lipid bilayer down their concentration gradient without requiring a transport protein or cellular energy.

Facilitated Diffusion

The passive transport of polar or charged substances across a membrane down their concentration gradient using channel or carrier proteins without requiring energy.

Active Transport

The transport of substances across a membrane against their concentration gradient, which requires both a transport protein and the input of cellular energy (such as $ATP$).

ATP/ADP Cycle

The cellular cycle of spending energy by removing an inorganic phosphate from $ATP$ to yield $ADP$, and storing energy by reattaching a phosphate to charge $ADP$ back to $ATP$.

Gluconeogenesis

The anabolic process of synthesizing glucose, which serves as the reverse pathway of glycolysis and is allosterically regulated and stimulated by an accumulation of acetyl CoA.

Acetyl CoA

A two-carbon molecule formed by the oxidative decarboxylation of pyruvate in the mitochondria that serves as the primary starting fuel for the citric acid cycle.

Oxaloacetate

A four-carbon intermediate that condenses with the two-carbon acetyl CoA to form six-carbon citrate, and is regenerated at the completion of each citric acid cycle turn.

Citric Acid Cycle

A mitochondrial metabolic cycle (also termed the Krebs or TCA cycle) that oxidizes acetyl groups, trims carbons off as $CO_2$, and generates $1\text{ ATP}$, $3\text{ NADH}$, and $1\text{ FADH}_2$ per acetyl CoA.

ATP Synthase

A rotary turbine-like membrane enzyme that converts $ADP$ to $ATP$ as protons ($H^+$) flow down their electrochemical gradient, synthesizing $1\text{ ATP}$ for every $3\,H^+$ that pass through.

Iron-Sulfur Proteins

A class of electron transport carriers containing iron prosthetic centers that alternate between reduced and oxidized states to shuffle electrons.

Cytochromes

Electron transport chain proteins containing a heme group with an iron atom held by nitrogen atoms that functions as an electron carrier.

Coenzyme Q

A non-protein electron carrier within the electron transport chain that can be successively reduced in two steps, existing in uncharged, semi-charged, and fully charged states.

Meiosis

A specialized cell division process whose primary purpose is to prepare for sexual reproduction by generating genetically diverse gametes possessing one copy of chromosomes.

Protein Domain

A specific structural and functional region of a protein that performs a distinct cellular task.

Golgi Apparatus

A eukaryotic membrane-bound organelle that acts like an "Amazon distribution center" by receiving, sorting, and packaging cellular products.

Endosymbiont Theory

The evolutionary model proposing that eukaryotic organelles, notably mitochondria and chloroplasts, originated from ancient engulfed prokaryotes.

Phototrophs

Organisms that capture their metabolic energy directly from sunlight.

Chemotrophs

Organisms that acquire their metabolic energy through the intake and chemical breakdown of ingested chemical compounds.

Open System

A thermodynamic system, such as a living cell, capable of importing nutrients and exporting waste products to regulate chemical concentrations.

Closed System

A sealed physical system in which matter can neither enter nor exit.

Equilibrium Constant ($K_{eq}$)

The mathematical ratio of products to reactants ($\frac{[\text{products}]}{[\text{reactants}]}$) at equilibrium; a high $K_{eq}$ indicates a reaction that strongly favors products and has a highly negative $\Delta G$.

Activation Energy

The threshold amount of initial energy required to start a chemical reaction, which enzymes accelerate by lowering this barrier.

Aquaporins

Specialized channel proteins embedded in biological membranes that facilitate the rapid passive movement of water molecules to regulate osmosis.

Uniport

A membrane carrier protein that transports a single type of solute across the membrane in one direction.

Symport

A coupled membrane transporter that moves two distinct solute molecules simultaneously across the membrane in the same direction.

Antiport

A coupled membrane transporter that moves two distinct solute molecules across the membrane in opposite directions.

Sodium-Potassium Pump

An active antiport transporter that hydrolyzes $1\text{ ATP}$ to pump three sodium ions ($3\,Na^+$) out of the cell and two potassium ions ($2\,K^+$) into the cell against their electrochemical gradients.

Axon

A long, slender protrusion of a neuron responsible for conducting electrical impulses away from the cell body toward target cells.

Proteolysis

The enzymatic cleavage of peptide bonds linking amino acids in proteins, allowing carbon skeletons (such as aspartate or glutamate) to feed into the citric acid cycle.

Amphibolic Pathway

A metabolic route that functions in both breaking down molecules (catabolism) and building up macromolecules (anabolism), exemplified by the citric acid cycle.

Glycolysis

A metabolic pathway occurring freely in the cytoplasm that breaks down a six-carbon glucose molecule into two molecules of pyruvate.

Reduction

The addition of electrons (or hydrogenation) to a molecule, which decreases its chemical charge and transfers potential energy to it.

Oxidation

The removal of electrons (or dehydrogenation) from a molecule, which releases energy and leaves the carrier in an uncharged state.

Fluid Mosaic Model

A structural representation of biological membranes where lipids provide two-dimensional fluidity and embedded proteins form a heterogeneous pattern.

FRAP (Fluorescence Recovery After Photobleaching)

An experimental technique that uses a focused laser to bleach a fluorophore-labeled membrane patch and measures the rate of lateral diffusion.

Unsaturated Fatty Acids

Hydrocarbon chains containing one or more cis double bonds that introduce permanent bends, preventing tight packing and increasing membrane fluidity.

Saturated Fatty Acids

Hydrocarbon chains lacking double bonds that remain straight and pack tightly together, decreasing membrane fluidity and raising phase transition temperatures.

Cholesterol Fluidity Buffering

The bidirectional modulation of bilayer dynamics by sterols, which restrict acyl chain motion at warm temperatures while preventing rigid gel packing at cold temperatures.

Steroid Structure

A characteristic lipid architecture composed of a rigid four-ring hydrocarbon skeleton, colloquially described as "three rooms and a garage."

Phosphoglycerolipids

Membrane lipids consisting of a glycerol backbone esterified to two fatty acid chains and a phosphate head group linked to an alcohol.

Glycolipids

Membrane lipids attached to one or more carbohydrate residues that predominantly face the extracellular leaflet to facilitate recognition and cell protection.

Glycoproteins

Cell-surface proteins covalently linked to oligosaccharide chains that project outward into the extracellular space to facilitate cell-cell recognition.

Membrane Asymmetry

The unequal, non-random distribution of distinct lipids, carbohydrates, and protein orientations between the inner and outer monolayers of a lipid bilayer.

Transverse Diffusion (Flip-Flop)

The rare, uncatalyzed movement of a lipid molecule from one membrane leaflet to the opposite one, hindered by the thermodynamic penalty of dragging a polar head group through the hydrophobic core.

Integral Membrane Proteins

Polypeptides embedded directly within the lipid bilayer, typically spanning the membrane via hydrophobic $\alpha$-helices and requiring detergent treatment for extraction.

Peripheral Membrane Proteins

Polypeptides non-covalently associated with the membrane surface via electrostatic interactions and hydrogen bonding with lipid head groups or transmembrane proteins, removable by high salt or $pH$ shifts.

Lipid-Anchored Proteins

Surface polypeptides that do not enter the hydrophobic bilayer directly but are tethered through covalent bonds to embedded fatty acids, prenyl groups, or GPI anchors.

Simple Diffusion

The direct, unaided passive movement of small or nonpolar solutes across the lipid bilayer down a concentration gradient without transport proteins or energy input.

Facilitated Diffusion

Passive transport of polar or charged solutes down an electrochemical gradient using transmembrane channel or carrier proteins without expending cellular energy.

Active Transport

The movement of solutes across a biological membrane against an electrochemical gradient, mediated by transport carriers that expend cellular energy such as $ATP$.

Concentration Gradient

A difference in the concentration of a chemical solute between two distinct regions or across a membrane, establishing potential chemical energy.

Osmosis

The net movement of water solvent molecules across a semipermeable membrane from an area of lower solute concentration toward an area of higher solute concentration.

Catabolic Pathway

An exergonic, oxidative sequence of metabolic reactions that breaks down complex organic fuels into simpler end products, generating free energy and reducing equivalents.

Anabolic Pathway

An endergonic, reductive sequence of biosynthetic reactions that constructs complex cellular macromolecules from simpler precursor molecules, consuming chemical energy.

ATP/ADP Cycle

The cellular cycle of spending energy by removing an inorganic phosphate from a nucleotide triphosphate to yield a diphosphate, and capturing energy by re-phosphorylating it.

Nicotinamide Adenine Dinucleotide ($NAD^+/NADH$)

A soluble dinucleotide coenzyme that accepts two electrons and one proton to shuttle reducing potential from catabolic reactions to the electron transport chain.

Glycolysis Phase 1 (Energy Investment Phase)

The initial stage of carbohydrate breakdown where two molecules of $ATP$ are consumed to phosphorylate glucose into fructose-1,6-bisphosphate before cleavage into two three-carbon trioses.

Glycolysis Phase 2 (Oxidation and First Payoff)

The stage of carbohydrate breakdown where glyceraldehyde-3-phosphate is oxidized to generate two molecules of $NADH$ and two molecules of $ATP$ via substrate-level phosphorylation.

Glycolysis Phase 3 (Pyruvate Formation and Second Payoff)

The terminal stage of glucose catabolism where phosphoenolpyruvate transfers high-energy phosphate groups to $ADP$, generating two molecules of $ATP$ and yielding two pyruvate molecules.

Fermentation

An anaerobic metabolic process that transfers electrons from $NADH$ onto pyruvate or its derivatives to regenerate oxidized $NAD^+$, maintaining glycolysis with a net yield of $2\text{ ATP}$.

Gluconeogenesis

The anabolic synthesis of glucose from non-carbohydrate precursors, utilizing distinct bypass enzymes to overcome the three irreversible thermodynamic bottlenecks of glycolysis.

Allosteric Activation of Gluconeogenesis

The stimulation of glucose synthesis by high concentrations of acetyl CoA, which turns on pyruvate carboxylase while inhibiting pyruvate dehydrogenase.

Acetyl CoA

A two-carbon acetyl group coupled to a coenzyme carrier, synthesized from pyruvate decarboxylation or fatty acid breakdown, that acts as the primary starting fuel for the citric acid cycle.

Oxaloacetate

A four-carbon metabolic intermediate that condenses with an incoming two-carbon acetyl group to initiate the citric acid cycle and is regenerated at each turn's completion.

Citric Acid Cycle

A mitochondrial circular metabolic pathway that completely oxidizes two-carbon acetyl units into $CO<em>2$, generating $1\text{ ATP}$, $3\text{ NADH}$, and $1\text{ FADH}</em>2$ per turn.

ATP Synthase

A membrane-bound rotary nanomachine that couples the spontaneous flow of protons ($H^+$) down their electrochemical gradient to the condensation of $ADP$ and inorganic phosphate, yielding $1\text{ ATP}$ per three protons.

Iron-Sulfur Proteins

Electron transport carriers containing non-heme iron coordinated with inorganic sulfur atoms that alternate between reduced and oxidized oxidation states to transfer electrons.

Cytochromes

Electron transport chain hemoproteins containing an iron porphyrin prosthetic ring held by nitrogen atoms that cycles between ferric and ferrous states to pass electrons.

Coenzyme Q

A non-protein, lipid-soluble electron shuttle within the inner mitochondrial membrane that undergoes stepwise reduction through uncharged, semiquinone, and fully reduced ubiquinol states.

Aquaporins

Tetrameric channel proteins embedded in biological membranes that facilitate the rapid, bidirectional passive flux of water molecules across lipid bilayers.

Uniport

A carrier transport protein that moves a single solute species across a biological membrane down its electrochemical gradient in one direction.

Symport

A coupled secondary active transporter that moves two distinct solute species simultaneously across a membrane in the same direction.

Antiport

A coupled secondary active transporter that moves two distinct solute species across a membrane in opposite directions.

Sodium-Potassium Pump

A primary active antiport ATPase that hydrolyzes one molecule of $ATP$ to export three sodium ions ($3\,Na^+$) and import two potassium ions ($2\,K^+$) against their concentration gradients.

Equilibrium Constant ($K_{eq}$)

The mathematical ratio of product concentrations to reactant concentrations at equilibrium; values greater than 1 correspond to a reaction with a negative standard free energy change ($\Delta G^\circ$).

Activation Energy

The initial kinetic energy barrier that reactants must overcome to reach the transition state, which biocatalysts accelerate by lowering.

Meiosis

A specialized reductional cell division program that produces genetically distinct haploid gametes containing a single chromosomal set for sexual reproduction.

Protein Domain

A distinct, compact, modular region of a polypeptide chain that folds independently and carries out a specific biochemical or structural task.

Golgi Apparatus

A eukaryotic membrane-bound organelle consisting of flattened cisternae that receives, chemically modifies, sorts, and packages macromolecules for secretion or organellar delivery.

Endosymbiont Theory

The evolutionary explanation stating that mitochondria and chloroplasts arose from free-living prokaryotes that were engulfed by ancestral host cells and established mutualistic relationships.

Phototrophs

Organisms capable of transforming electromagnetic radiant energy from sunlight into chemical energy to sustain cellular metabolism.

Chemotrophs

Organisms that derive metabolic energy solely by the oxidative catabolism of preformed environmental organic or inorganic chemical compounds.

Open System

A thermodynamic framework, exemplified by a living cell, that continuously exchanges matter and energy with its surrounding environment to maintain non-equilibrium steady states.

Closed System

A sealed thermodynamic framework that permits energy transfer with the surroundings but completely prevents the exchange of physical matter.

Axon

A slender, elongated cylindrical projection of a neuron that propagates action potentials away from the soma toward target effector cells or synapses.

Proteolysis

The enzymatic hydrolysis of peptide bonds in proteins, releasing carbon skeletons that can enter central catabolism via conversion into citric acid cycle intermediates.