Unit 2: Cell Biology, Membrane Transport, and Cell Specialization

Comprehensive practice flashcards defining core vocabulary terms covering the origins of cells, membrane structure and transport, organelle compartmentalization, and specialized cell adaptations.

Miller-Urey Experiment

An origin-of-life simulation demonstrating that inorganic atmospheric gases (ammonia, methane, hydrogen, and water vapor) subjected to electrical discharge could spontaneously generate 20 amino acids.

Primordial Soup

The accumulation of early organic carbon compounds—including carboxylic acids, aldehydes, amino acids, and nitrogenous bases—concentrated in early Earth's pools, lakes, or oceans.

RNA World Hypothesis

The proposition that RNA served as the first genetic material because it stores genetic sequence information like DNA while also acting as an enzyme (ribozyme) capable of self-replication and peptide bond catalysis.

Ribozymes

Enzymatically active RNA molecules within ribosomes that catalyze chemical reactions, notably the formation of peptide bonds between amino acids during protein synthesis.

LUCA (Last Universal Common Ancestor)

The ancestral cellular organism common to all extant life, characterized by universal use of the 64 genetic codons, ribosomal structures, and roughly 355 shared protein families adapted for anaerobic metabolism in hydrothermal vents.

Stromatolites

Fossilized microbial rock structures, such as those discovered in Western Australia, providing evidence for early cellular life and LUCA dating back to at least 3.42 billion years ago.

Fluid-Mosaic Model

A biological model describing the plasma membrane as a flexible phospholipid bilayer embedded with a mosaic of mobile proteins, cholesterol, glycoproteins, and glycolipids.

Unsaturated Hydrocarbon Tails

Fatty acid chains possessing double bonds that create kinks, lowering their melting points and preserving membrane fluidity and flexibility at cold temperatures.

Cholesterol

An amphipathic lipid interspersed among phospholipids in animal membranes that prevents excessive fluidity at high temperatures and prevents crystallization at low temperatures, stabilizing permeability.

Integral Proteins

Permanent membrane proteins that penetrate into or fully span across one or more hydrophobic layers of the lipid bilayer, often functioning in transport or signal transduction.

Peripheral Proteins

Membrane proteins that adhere non-covalently to the outer or inner surface of the lipid bilayer rather than embedding within its hydrophobic core.

Aquaporins

Specialized integral membrane channel proteins that dramatically increase membrane permeability to facilitate the rapid, passive movement of water molecules by osmosis.

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

An integral primary active transport protein that uses ATP hydrolysis to pump sodium ($\text{Na}^+$) ions out of the cell and potassium ($\text{K}^+$) ions into the cell against their electrochemical gradients.

Sodium-Dependent Glucose Cotransporter

A secondary active transport symporter that utilizes the potential energy of $\text{Na}^+$ flowing down its concentration gradient into the cell to drive the concurrent inward transport of glucose against its gradient.

Hypertonic Solution

An external solution with a higher solute concentration than the cytoplasm, causing net water movement out of the cell via osmosis and causing the cell to shrink.

Hypotonic Solution

An external solution with a lower solute concentration than the cytoplasm, causing net water influx into the cell via osmosis and resulting in cell swelling or bursting.

Isotonic Solution

An external solution possessing an equal solute concentration relative to the cytoplasm, resulting in no net movement of water and maintaining normal cell volume.

Cell Adhesion Molecules (CAMs)

Transmembrane proteins embedded in the cell surface that bind adjacent cells together, forming junctions essential for maintaining tissue and organ architecture.

Compartmentalization

The segregation of distinct cellular processes within membrane-bound organelles, allowing toxic wastes to be isolated, optimal pH to be maintained, and enzymes to concentrate with their substrates.

Endosymbiosis

The evolutionary process by which an anaerobic ancestral eukaryote engulfed aerobic and photosynthetic prokaryotes, which persisted symbiotically and evolved into mitochondria and chloroplasts.

Mitochondrial Cristae

Extensive infoldings of the inner mitochondrial membrane that expand the total surface area available for the electron transport chain and ATP synthase particles.

Thylakoids

Flattened, disc-shaped membranous sacs within chloroplasts arranged in stacks called grana, providing an expanded surface area to absorb light during photosynthesis.

Nuclear Membrane Pore

Large protein complexes spanning the double-membrane nuclear envelope that regulate the bidirectional exchange of macromolecules, including ribosomal subunits, RNA, and proteins.

Clathrin

A triskelion-shaped structural protein that polymerizes into a polygonal lattice coating budding membranes, inducing curvature to drive clathrin-coated vesicle formation.

Cell Differentiation

The developmental specialization of cells wherein specific sets of genes are selectively transcribed and expressed, producing distinct cellular structures and biochemical functions.

Stem Cell Niche

A specialized in vivo microenvironment that provides physical anchoring and chemical signals to keep adult stem cells quiescent and undifferentiated until tissue regeneration is required.

Totipotent Stem Cells

Embryonic stem cells present in early cleavage-stage embryos capable of giving rise to all embryonic and extraembryonic cell types, possessing the potential to form entire organisms or organs.

Pluripotent Stem Cells

Stem cells from later-stage blastocysts capable of differentiating into nearly any somatic cell lineage across the three germ layers, but not extraembryonic tissues.

Multipotent Stem Cells

Lineage-restricted adult stem cells, such as hematopoietic stem cells in bone marrow, that differentiate only into a closely related family of functional mature cells.

Surface Area-to-Volume Ratio

A geometric ratio that decreases as cell volume increases, constraining maximal cell dimensions due to limits on diffusion rate, nutrient absorption, waste removal, and thermal regulation.

Microvilli

Tightly packed, microscopic brush-border membrane protrusions that dramatically expand the apical surface area of proximal tubule epithelial cells to optimize tubular reabsorption.

Type I Pneumocytes

Extremely flat and attenuated squamous alveolar cells that line the pulmonary air sacs, minimizing diffusion distance to facilitate rapid gas exchange between alveolar air and capillary blood.

Type II Pneumocytes

Cuboidal alveolar epithelial cells that synthesize and secrete pulmonary surfactant, decreasing alveolar surface tension to prevent alveolar collapse during expiration.

Cardiac Muscle

Involuntary, branched, and striated muscle tissue containing intercalated discs that electrically couple adjacent cardiomyocytes to synchronize rhythmic heart contractions.

Acrosome

An anterior lysosome-like vesicle capping the sperm head that contains hydrolytic enzymes used to digest through the protective zona pellucida of the ovum during fertilization.

Zona Pellucida

A protective, thick extracellular glycoprotein coat surrounding the ovum that mediates sperm binding and undergoes enzymatic hardening after fertilization to prevent polyspermy.

Cortical Granules

Secretory vesicles positioned beneath the ovum's plasma membrane that undergo exocytosis upon sperm entry, releasing modifying enzymes that render the zona pellucida impenetrable.

Free Ribosomes

Unbound ribosomes suspended in the cytosol that synthesize water-soluble polypeptides destined to remain and function directly within the intracellular cytoplasm.

Bound Ribosomes

Ribosomes anchored to the cytosolic face of the rough endoplasmic reticulum that translate polypeptides destined for membrane insertion, lysosomal packaging, or extracellular secretion.

Plastids

A diverse class of double-membrane organelles found exclusively in plant cells, including photosynthetic chloroplasts and starch-storing amyloplasts, which are absent in animals and fungi.