BIOL 1090 Comprehensive Cell Biology Review

Vocabulary practice flashcards covering cell structure, viral biology, membrane transport, the endomembrane system, cytoskeleton, cellular energetics, and nuclear import from the BIOL 1090 review materials.

Virion

An inanimate virus particle existing outside of a host cell, consisting of a protein capsid enclosing a small genetic payload of DNA or RNA.

Capsid

The outer protein shell or capsule that packages and protects the viral nucleic acid genome.

Bacteriophage

A virus that infects bacterial cells, structurally composed of a DNA-containing capsid head, collar, sheath, baseplate, spikes, and tail fibers.

Provirus

Viral DNA that is stably inserted into the host cell's genome during a non-lytic (integrative or lysogenic) infection, allowing the host cell to survive, often with impaired function.

Lytic Infection

A viral infection pathway in which the virus hijacks cellular machinery to produce new virions until the host cell ruptures and dies.

Fluid Mosaic Model

The membrane model describing a fluid phospholipid bilayer wherein individual lipid molecules diffuse laterally while diverse proteins, carbohydrates, and cholesterol penetrate or associate with the layer.

Transition Temperature

The distinct temperature at which a biological membrane converts between a rigid crystalline gel state and a fluid liquid-crystal state.

Integral Membrane Protein

A transmembrane protein that permanently spans the hydrophobic core of the lipid bilayer, functioning in transport, attachment, or cell-cell signaling.

Peripheral Membrane Protein

A protein that temporarily associates with the hydrophilic polar head groups or surface of integral membrane proteins without entering the hydrophobic core of the lipid bilayer.

Lipid-Anchored Protein

A protein located on the membrane surface that is covalently attached to a lipid molecule embedded within the bilayer.

Voltage-Gated Ion Channel

An ion channel whose opening and closing conformational transitions are regulated by changes in electrical potential across the plasma membrane.

Ligand-Gated Ion Channel

An ion channel whose opening is triggered by the specific binding of a chemical messenger (ligand) to its receptor site.

Facilitated Diffusion

Passive, carrier-mediated transport that relies on a specific integral membrane protein undergoing a conformational change to transfer a solute down its concentration gradient without energy consumption.

Antiporter

A carrier protein that harnesses the concentration gradient of one solute moving down its electrochemical gradient to drive the transport of a second solute in the opposite direction across the membrane.

Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ Pump)

An active transport pump that hydrolyzes ATP to export $3\,\text{Na}^+$ ions from the cell while importing $2\,\text{K}^+$ ions into the cell against their respective concentration gradients.

Extracellular Matrix (ECM)

A dynamic macromolecular network of secreted glycoproteins, collagens, glycosaminoglycans, and proteoglycans that provides bulk, shape, and mechanical support to animal tissues.

Integrin

An integral membrane anchor protein that attaches cells to extracellular matrix components and transduces external mechanical or chemical cues into intracellular signaling events.

Substrate-Level Phosphorylation

The direct transfer of a phosphate group to ADP from a phosphorylated metabolic intermediate via a hydrolysis reaction, accounting for approximately $12\%$ of ATP produced in aerobic respiration.

Oxidative Phosphorylation

The metabolic process wherein electrons derived from organic molecules pass through Complexes I–IV of the electron transport chain to generate a proton gradient that drives ATP synthesis, yielding approximately $88\%$ of cellular ATP.

Intrinsic Pathway of Apoptosis

A mitochondria-driven programmed cell death cascade initiated by intracellular damage, where activated BAX or BAK proteins permeabilize the outer mitochondrial membrane to release Cytochrome c into the cytosol.

Axonemal Microtubules

Highly organized, stable microtubule arrays found in cilia and flagella that facilitate structural support and motile bending.

Tau

A non-motor microtubule-associated protein (MAP) that stabilizes and organizes parallel arrays of neuronal microtubules.

Porin

A transmembrane protein forming large, open, water-filled channels in the outer mitochondrial membrane that allow the passive diffusion of small molecules.

Rough Endoplasmic Reticulum (RER)

The ribosome-studded subdomain of the endoplasmic reticulum responsible for the synthesis of membrane and secretory proteins, initial glycosylation, and chaperone-assisted protein folding.

Smooth Endoplasmic Reticulum (SER)

The agranular subdomain of the endoplasmic reticulum that lacks ribosomes and specializes in lipid synthesis, steroid hormone production, detoxification, and $\text{Ca}^{2+}$ sequestration.

ER Signal Sequence

A peptide sequence situated at the amino-terminus (N-terminus) of a nascent protein consisting of consecutive hydrophobic amino acids that targets the translation complex to the rough ER membrane.

Signal Recognition Particle (SRP)

A cytosolic ribonucleoprotein complex that recognizes the ER signal sequence on a nascent polypeptide, halts elongation, and docks the ribosome onto the ER SRP receptor.

Translocon

An aqueous protein conduction channel embedded within the rough ER membrane that allows nascent polypeptides to enter the ER lumen cotranslationally.

Signal Peptidase

An ER luminal enzyme that cleaves the N-terminal signal peptide from a translocating polypeptide once inside the lumen.

BiP

An ER lumen-resident molecular chaperone that binds newly translocated polypeptides to assist in proper protein folding and quality control.

Signal-Anchor Sequence

An internal hydrophobic peptide sequence within a nascent polypeptide that halts translocation and discharges laterally into the bilayer to become a transmembrane domain.

TOM Complex

The Translocase of the Outer Membrane; a multisubunit outer mitochondrial membrane complex responsible for recognizing and importing nuclear-encoded proteins from the cytosol into the mitochondrion.

Anterograde Transport

Directional membrane trafficking that moves cargo forward from proximal to distal compartments: from the ER to the cis-Golgi network, through the cisternae to the trans-Golgi network, and out toward the plasma membrane.

Retrograde Transport

Directional membrane trafficking that moves vesicles backward from distal to proximal compartments, such as from the Golgi back to the ER or from later to earlier Golgi cisternae.

Cisternal Maturation

The dynamic progression model of Golgi transport where cis-cisternae physically mature into medial- and trans-cisternae as retrograde vesicles retrieve processing enzymes back to earlier compartments.

Constitutive Secretion

An unprompted, continuous secretory pathway operating in all eukaryotic cells that continually delivers newly synthesized lipids and proteins to the cell surface and extracellular space.

Regulated Secretion

A specialized secretory pathway where concentrated cargo is packaged in dense-core granules and stored until a specific external signal, such as an influx of $\text{Ca}^{2+}$, triggers exocytosis.

Vesicle Coat Proteins (COPI, COPII, Clathrin)

Protein complexes that assemble on donor membranes to drive membrane curvature and cargo selection: COPII mediates ER-to-Golgi transport, COPI mediates retrograde transport, and Clathrin functions at the TGN, plasma membrane, and endosomes.

Sar1

A regulatory GTPase that recruits coat protein subunits to the endoplasmic reticulum membrane to initiate the assembly of the COPII coat.

SNARE Complex

A four-helix bundle formed by the pairing of vesicle v-SNARE proteins with target membrane t-SNARE proteins, bringing the lipid bilayers into close apposition to drive membrane fusion.

Acid Hydrolases

A diverse class of digestive enzymes residing within the lysosome whose optimal catalytic activity is confined to an acidic environment around $\text{pH } 4.6$.

Autophagy

A regulated cellular recycling pathway where an ER-derived isolation membrane (phagophore) encloses damaged organelles or cytosolic proteins into an autophagosome, which subsequently fuses with a lysosome for degradation.

Microtubules

Hollow, rigid cytoskeletal cylinders measuring approximately $25\,\text{nm}$ in outer diameter, built from 13 parallel protofilaments of $\alpha$- and $\beta$-tubulin heterodimers that possess distinct plus (+$) and minus (-$$) polar ends.

Intermediate Filaments

Non-polar, unbranched rope-like cytoskeletal fibers roughly $10\,\text{nm}$ in diameter formed from antiparallel tetramers of coiled-coil dimers that provide high tensile mechanical strength without supporting motor proteins.

Microfilaments (Actin Filaments)

Thin, polarized cytoskeletal polymers measuring roughly $7\,\text{nm}$ in diameter formed by two helical strands of globular actin (G-actin) polymerized head-to-tail into filamentous actin (F-actin).

Treadmilling

A dynamic steady-state behavior of microfilaments in which ATP-actin monomers associate continuously at the plus (+$) end while ADP-actin monomers dissociate at the minus (-$$) end at an equivalent rate.

Microtubule-Organizing Centre (MTOC)

The eukaryotic nucleating structure (such as the centrosome or basal body) that controls the assembly, polarity, and orientation of microtubules, anchoring their minus ($-$) ends.

Kinesin

An ATP-driven motor protein family that moves processively along microtubules toward the plus ($$+$) end, directing anterograde outward transport of vesicles and organelles.

Dynein

A minus-end-directed microtubule motor protein that utilizes ATP hydrolysis to power retrograde inward transport toward the MTOC near the cell center.

Conventional Myosin (Type II)

A two-headed actin-associated motor protein that pulls actin filaments past one another to generate contractile force in muscle and non-muscle cells.

Nuclear Lamina

A fibrous protein meshwork of intermediate filaments (lamins) lining the inner nuclear membrane that provides mechanical scaffolding and chromatin anchoring sites.

Nuclear Pore Complex (NPC)

A large, octagonal basket-like supramolecular structure composed of nucleoporins that spans the inner and outer nuclear membranes to regulate nucleocytoplasmic traffic.

Nuclear Localization Signal (NLS)

A specific targeting sequence enriched in basic, positively charged amino acids on a folded protein that allows its recognition by transport receptors for regulated entry through the nuclear pore complex.

Nucleolus

The prominent, non-membrane-bound subnuclear compartment dedicated to transcribing ribosomal RNA (rRNA), processing transcripts, and assembling 40S and 60S ribosomal subunits.