Review Seminar 1: Cell Biology, Membranes, Viruses, and Bioenergetics

Vocabulary practice flashcards covering cell structure, viral biology, membrane composition and dynamics, transport mechanisms, signal transduction, the extracellular matrix, bioenergetics, and apoptosis.

Prokaryotic Cell

A single-celled organism typically $1\text{--}10\,\mu\text{m}$ in size that lacks a nucleus or membrane-bound organelles, possesses small ribosomes, reproduces asexually, and contains circular DNA (plasmid) located in a nucleoid.

Eukaryotic Cell

A cell type typically $10\text{--}100\,\mu\text{m}$ in size found in multicellular organisms or unicellular protozoa, characterized by membrane-bound organelles, a defined nucleus, large ribosomes, and genetic material organized into linear chromosomes.

Virion

An inanimate viral particle existing outside host cells, consisting of a protein capsule called a capsid surrounding a small amount of DNA or RNA encoding a few hundred genes.

Bacteriophage

A virus that infects bacterial cells, typically composed of a capsid head containing nucleic acid (DNA), collar, sheath, baseplate, spikes, and tail fibers.

Viral Host Range

The specific group of host species or cell types a virus can infect based on surface protein binding, classified as narrow (e.g., cold and influenza viruses infecting human respiratory epithelial cells) or wide (e.g., rabies infecting dogs, foxes, bats, raccoons, and humans).

Lytic Infection

A viral infection pathway in which the virus hijacks host cellular machinery to assemble new viral particles, culminating in host cell rupture and death (e.g., influenza, T4 bacteriophage).

Non-Lytic (Integrative/Lysogenic) Infection

A viral infection mode where viral DNA integrates directly into the host genome as a provirus, allowing the host cell to survive, often with impaired function (e.g., HIV, chickenpox).

Provirus

Viral DNA that has integrated into the genome of a host cell during a non-lytic (integrative or lysogenic) infection.

Plasma Membrane

A trilaminar phospholipid bilayer approximately $6\,\text{nm}$ thick that encloses cell compartments, regulates selective transport, mediates responses to stimuli, and provides a scaffold for biochemical activities.

Phospholipid

An amphipathic molecule composed of two hydrophobic fatty acid chains and a glycerol backbone attached to a hydrophilic polar head group linked by a phosphate residue.

Fluid Mosaic Model

A model of biological membranes describing a dynamic phospholipid bilayer wherein lipids move easily laterally within leaflets, embedded with diverse mosaic components including proteins, carbohydrates, and cholesterol.

Membrane Asymmetry

The distinct and unequal lipid and protein compositions of the inner and outer leaflets of the plasma membrane, such as the preferential presentation of glycolipids and glycoproteins on the outer leaflet.

Transition Temperature (Membrane)

The specific temperature at which a biological membrane shifts between a rigid crystalline gel state and a fluid-like liquid crystal state.

Membrane Fluidity Modulators

Lipid characteristics that regulate membrane viscosity: unsaturated fatty acids increase fluidity due to double-bond kinks, saturated fatty acids decrease fluidity by packing tightly, and cholesterol buffers fluidity across different temperature regimes.

Integral Membrane Protein

A transmembrane protein that spans the hydrophobic core of the lipid bilayer, functioning in nutrient/ion transport, attachment, and cell-cell communication.

Peripheral Membrane Protein

A protein associated non-covalently with the hydrophilic surfaces of the lipid bilayer rather than embedding within the hydrophobic interior.

Lipid-Anchored Protein

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

Simple Diffusion

A non-mediated passive transport mechanism in which small, uncharged molecules (such as $\text{O}_2$, $\text{CO}_2$, and $\text{NO}$) diffuse downhill along their concentration gradient directly through the lipid bilayer without energy.

Ion Channel

A selective, gated integral membrane protein complex forming an aqueous pore that permits small charged ions (such as $\text{Na}^+$, $\text{K}^+$, $\text{Ca}^{2+}$, and $\text{Cl}^-$) to diffuse downhill passively along their electrochemical gradients.

Voltage-Gated Ion Channel

An ion channel (such as a $\text{Na}^+$ or $\text{K}^+$ channel) that opens or closes in response to alterations in electrical charge across the plasma membrane.

Ligand-Gated Ion Channel

An ion channel (such as the acetylcholine receptor) that opens or closes upon the conformational change caused by the specific binding of a ligand molecule to its surface.

Facilitated Diffusion

A passive, carrier-mediated transport mechanism wherein a solute binds specifically to an integral facilitative transporter, inducing a conformational change that moves the compound across without requiring energy.

Carrier Protein Types (Uniporter, Symporter, Antiporter)

Transporters classified by movement mechanics: uniporters move a single molecule; symporters cotransport two molecules in the same direction; antiporters move two molecules in opposite directions using one gradient to drive the other.

Active Transport

Transporter-mediated translocation that moves compounds against a concentration gradient via conformational changes powered by the hydrolysis of $\text{ATP}$.

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

An active transporter that consumes $\text{ATP}$ to pump $3\,\text{Na}^+$ ions out of the cell and $2\,\text{K}^+$ ions into the cell against their concentration gradients.

Ligand (Signal Transduction)

A small signaling molecule that binds to a specific receptor on the cell exterior without entering the cell, triggering conformational changes that activate downstream intracellular responses.

Second Messenger

An intracellular relay molecule (such as $\text{cAMP}$, calcium, or G-proteins) that propagates and amplifies signals within the cytoplasm following receptor activation.

Extracellular Matrix (ECM)

A dynamic extracellular meshwork of secreted glycoproteins, collagens, glycosaminoglycans, and proteoglycans that gives tissues bulk, shape, and mechanical support.

Integrin

An integral membrane anchor protein at the cell surface that acts as a receptor for extracellular matrix components, transmitting signals that coordinate cell attachment and behavior.

Plant Cell Wall

A rigid extracellular matrix surrounding plant cells composed of cellulose, hemicellulose, pectin, and proteins that provides organismal structural support and protects against mechanical damage and pathogens.

Aerobic Respiration

A catabolic pathway occurring in the presence of oxygen that converts chemical energy in food molecules into $\text{ATP}$, represented by $(\text{CH}_2\text{O}) + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{ATP}$.

Substrate-Level Phosphorylation

A process where a phosphate group is transferred directly from a substrate to $\text{ADP}$ to form $\text{ATP}$ during exergonic hydrolysis (e.g., in glycolysis and the Krebs cycle), generating about $12\%$ of animal cell ATP.

Oxidative Phosphorylation

A process wherein electron carriers transfer energy from organic molecules through the electron transport chain to generate a proton gradient powering $\text{ATP}$ synthase, producing approximately $88\%$ of ATP in animal cells.

Mitochondrion

A double-membrane organelle containing an outer membrane, an intermembrane space, inner membrane cristae, and a protein-dense matrix housing mitochondrial DNA and ribosomes, functioning in cellular respiration and apoptosis.

Electron Transport Chain (ETC)

A series of multiprotein complexes (Complexes I–IV) in the inner mitochondrial membrane that shuttle electrons to the terminal electron acceptor ($\text{O}_2$) while pumping protons into the intermembrane space.

Apoptosis

Programmed cell death characterized morphologically by cell shrinkage, plasma membrane blebbing, DNA and nuclear fragmentation, detachment from neighboring cells, and engulfment by phagocytic cells.

Intrinsic Pathway of Apoptosis

A mitochondria-driven cell death pathway triggered by intracellular damage, where pro-apoptotic proteins BAX and BAK permeabilize the outer mitochondrial membrane to release Cytochrome c, driving apoptosome formation and caspase activation.

Cytochrome c

A mitochondrial protein that, upon leakage into the cytoplasm through BAX/BAK pores, complexes with Apaf-1 and procaspase-9 to form an apoptosome that initiates caspase executioner cascades.