OnRamps Biology Unit 3-complete flashcard set

Comprehensive vocabulary flashcards covering membrane structure and dynamics, mechanisms of passive and active transport, basic prokaryotic and eukaryotic cell biology, organelle function and endosymbiosis, and cell signaling pathways.

Fluid-Mosaic Model

A biological model describing the plasma membrane as a dynamic matrix of phospholipids in which a mosaic of various proteins moves fluidly.

Phospholipid Bilayer

The structural foundation of cell membranes consisting of two parallel sheets of amphipathic phospholipids, where hydrophilic polar heads face aqueous environments and hydrophobic fatty acid tails face inward away from water.

Membrane Fluidity

The viscosity of the lipid bilayer, primarily governed by the saturation and length of fatty acid tails, cholesterol concentration, protein density, and temperature.

Frye-Edidin Experiment

A 1970 cell fusion experiment using human and mouse cells labeled with blue and red fluorescent antibodies, respectively, which completely intermixed within $40\,\text{minutes}$ following viral fusion, demonstrating lateral protein mobility in the membrane.

Cholesterol (Membrane Function)

A steroid lipid that acts as a membrane fluidity buffer by inserting between fatty acid tails to stabilize membrane fluidity, making up $25\text{--}30\%$ of lipids in animal cell membranes.

Lipid Rafts

Dense, highly organized microdomains in the membrane that contain elevated concentrations of saturated fatty acids and cholesterol, providing greater stability and lower fluidity to support specialized, heavier membrane proteins.

Membrane Carbohydrates

Short oligosaccharide chains covalently linked to membrane proteins (glycoproteins) or lipids (glycolipids) on the extracellular surface, functioning in cell-cell recognition, immunity, and cell identity (such as the $ABO$ blood groups).

Simple Diffusion

The passive, non-protein-mediated net movement of small, non-polar molecules (such as $O_2$, $CO_2$, ethanol, and steroids) down their concentration gradient until dynamic equilibrium is reached.

Osmosis

The passive net diffusion of water molecules across a selectively permeable membrane down its own concentration gradient, moving from an area of lower solute concentration to higher solute concentration.

Aquaporins

Transmembrane channel proteins that facilitate the rapid transport of water molecules into and out of cells across the hydrophobic core of the bilayer.

Tonicity

The capability of an extracellular solution to drive water movement into or out of a cell by osmosis, classified as isotonic, hypertonic, or hypotonic based on osmolarity differences.

Facilitated Diffusion

Passive transmembrane movement of polar molecules and ions down their concentration gradient with the assistance of carrier proteins or channel proteins, requiring no input of metabolic energy.

Carrier Proteins

Transmembrane transport proteins that selectively bind a specific solute and undergo conformational shape changes to shuttle that solute across the membrane.

Channel Proteins

Transmembrane proteins that form open hydrophilic pores through the membrane, allowing rapid passive diffusion of specific ions or small molecules.

Gated Ion Channels

Channel proteins that open or close their pores in response to specific stimuli—categorized as ligand-gated, voltage-gated, mechanically gated, or light-gated.

Active Transport

The cellular movement of substances across a membrane against their concentration or electrochemical gradient via transmembrane protein pumps, directly driven by the hydrolysis of $ATP$.

Sodium-Potassium Pump ($Na^+/K^+$ Pump)

An electrogenic primary active transport protein that hydrolyzes one molecule of $ATP$ to export three $Na^+$ ions and import two $K^+$ ions against their concentration gradients.

Proton Pump

An ancient electrogenic active transport protein conserved across Bacteria, Archaea, and Eukarya that hydrolyzes $ATP$ to move hydrogen ions ($H^+$) across biological membranes, creating a proton or $pH$ gradient.

Chemiosmosis

A cellular process in which the potential energy stored in an electrochemical proton ($H^+$) gradient across a membrane is harnessed to perform biological work.

Secondary Active Transport

A transport mechanism where an electrochemical gradient initially established by $ATP$-driven primary active transport (such as a proton gradient) is coupled to drive the simultaneous transport of a second solute against its concentration gradient.

Pinocytosis

A form of bulk endocytosis in which a cell invaginates its plasma membrane to engulf droplets of extracellular fluid and non-specific dissolved solutes into internal vesicles.

Endocytosis and Exocytosis

Bulk vesicular transport mechanisms: endocytosis brings extracellular materials into the cell inside membrane-bound vesicles, while exocytosis fuses intracellular vesicles with the plasma membrane to secrete substances.

Unified Cell Theory

A biological theory established in the 1830s by Schleiden and Schwann stating that all organisms are composed of cells, cells are the fundamental unit of life capable of life functions, and all cells arise from pre-existing cells.

Miller-Urey Experiment

A 1953 abiotic chemistry experiment showing that organic building blocks like amino acids and nucleic acid precursors can spontaneously form from inorganic molecules under early Earth conditions energized by electrical discharge.

Glycolysis

An ancient anaerobic catabolic pathway conserved in all three domains of life that breaks down simple sugar molecules to extract cellular energy and biogenic building blocks without requiring $O_2$.

Autotrophs

Organisms that synthesize their own organic food molecules from simple inorganic compounds (such as $CO_2$ and water), primarily utilizing light energy or inorganic chemical reactions.

Heterotrophs

Organisms that cannot fix carbon autonomously and must consume preformed organic matter generated by other organisms to acquire energy and carbon.

Prokaryotes

Single-celled organisms belonging to the domains Bacteria and Archaea that lack a nucleus and membrane-bound organelles, typically storing a single circular DNA chromosome in a nucleoid region.

Eukaryotes

Organisms containing compartmentalized cells characterized by a membrane-enclosed nucleus housing linear chromatin and complex membrane-bound organelles.

Endosymbiotic Theory

The evolutionary framework explaining that eukaryotic organelles like mitochondria and chloroplasts originated when ancestral eukaryotic cells engulfed aerobic bacteria and photosynthetic cyanobacteria, respectively.

Mitochondria

Double-membraned eukaryotic organelles with an inner folded membrane forming cristae and an internal fluid matrix; performs aerobic respiration to generate $ATP$ and contains circular $mtDNA$, $mtRNA$, and bacterial-sized ribosomes.

Chloroplasts

Double-membraned photosynthetic organelles found in plants and algae, composed of stacked thylakoid sacs called grana and a fluid stroma, housing circular $cpDNA$, $cpRNA$, and bacterial-sized ribosomes.

Cell Nucleus

The double-membraned organelle in eukaryotic cells that encloses chromatin, regulates gene transcription, mediates DNA replication during the cell cycle, and contains the nucleolus for ribosomal subunit assembly.

Ribosomes

Macromolecular complexes composed of ribosomal RNA ($rRNA$) and proteins consisting of large and small subunits that catalyze peptide bond formation during translation in both prokaryotic and eukaryotic cells.

Endomembrane System

A coordinated group of eukaryotic membranes and organelles—nuclear envelope, rough ER, smooth ER, transport vesicles, Golgi apparatus, lysosomes, and plasma membrane—that synthesize, modify, package, and transport proteins and lipids.

Rough Endoplasmic Reticulum

A region of the endomembrane system studded with ribosomes on its cytosolic surface, dedicated to the translation, folding, and initial modification of transmembrane and secretory proteins.

Smooth Endoplasmic Reticulum

A tubular membrane network lacking ribosomes that specializes in the synthesis of lipids (including phospholipids and steroid hormones), carbohydrate metabolism, and detoxification.

Golgi Apparatus

A eukaryotic organelle composed of flattened membranous cisternae that chemically modifies, sorts, tags, and packages proteins and lipids received from the ER for secretion or delivery to target organelles.

Lysosomes

Membrane-bound digestive organelles within animal cells that contain hydrolytic enzymes to break down engulfed biomolecules, cellular debris, and obsolete organelles.

Cell Signaling

The stepwise sequence of chemical interactions through which an extracellular chemical signal is detected by a cell and converted into a specific, altered cellular response through reception, transduction, and response.

Ligand

A specific chemical messenger molecule (such as a protein, peptide, or steroid) synthesized and released by a signaling cell that binds specifically to a target receptor protein.

Gap Junctions

Direct intercellular junctions in animal tissues formed by channel-like connexons (composed of connexin proteins) that allow small signaling molecules, ions, and electrical signals to flow directly between adjacent cytoplasms.

Plasmodesmata

Microscopic cytoplasmic channels traversing plant cell walls that connect the cytoplasm of neighboring plant cells, allowing direct intercellular transport and communication.

Paracrine Signaling

A mode of local cell communication where a cell secretes short-lived ligands that diffuse through the extracellular matrix to bind receptors on nearby target cells.

Synaptic Signaling

A specialized form of paracrine signaling where an electrical action potential travels down a neuron's axon, triggering the release of chemical neurotransmitters across a synapse to bind receptors on a dendrite or target cell.

Endocrine Signaling

Long-distance signaling in multicellular organisms in which specialized endocrine cells release hormones into the bloodstream, where they travel widely in low, diluted concentrations to elicit sustained target responses.

Autocrine Signaling

A mode of cell signaling in which a cell secretes chemical messengers that bind to receptors on its own surface or identical neighboring cells, regulating development, pain, inflammation, and apoptosis.

Intracellular Receptors

Receptor proteins located in the cytoplasm or nucleus that bind nonpolar, hydrophobic signaling molecules (such as steroid hormones) that diffuse across the plasma membrane, frequently functioning directly as transcription factors.

G Protein-Coupled Receptors (GPCRs)

A diverse class of transmembrane cell-surface receptors that undergo conformational change upon ligand binding, causing an associated heterotrimeric G protein's $\alpha$ subunit to exchange $GDP$ for $GTP$, dissociate, and trigger downstream signaling.

Receptor Tyrosine Kinases (RTKs)

Cell-surface enzyme-linked receptors that dimerize upon ligand binding, triggering cross-phosphorylation of tyrosine residues on their intracellular catalytic domains to activate intracellular relay proteins.

Ligand-Gated Ion Channel Receptors

Transmembrane channel receptors that undergo a structural conformational change and open a central pore in response to ligand binding, facilitating rapid ion flux across the cell membrane.

Phosphorylation Cascade

A sequential transduction chain reaction in which protein kinases iteratively transfer phosphate groups from $ATP$ to downstream enzymes, activating proteins and amplifying the original signal inside the cell.

Protein Kinase

An enzyme that catalyzes the covalent transfer of a phosphate group from an $ATP$ molecule to specific amino acid residues on a target protein, typically altering its conformation and catalytic activity.

Second Messengers

Small, non-protein intracellular signaling molecules or ions (such as $cAMP$, $Ca^{2+}$, or $IP_3$) that rapidly diffuse through the cytosol to relay and amplify signals initiated by membrane receptor activation.

Cyclic AMP ($cAMP$)

A ubiquitous second messenger synthesized from $ATP$ by adenylyl cyclase upon activation of GPCR pathways, which acts downstream to regulate specific protein kinases.