Biology of the Cell – Core Vocabulary

Key vocabulary terms from Chapter 4 covering cell structure, membrane components, transport mechanisms, signaling, organelles, genetic control, junctions, and cell division.

Cytology

The scientific study of cells, including their structure, function, and chemistry.

Microscopy

The use of microscopes and staining to visualize small-scale cellular structures.

Light Microscope (LM)

Instrument that passes light through a specimen to create a two-dimensional image.

Transmission Electron Microscope (TEM)

Electron microscope that provides highly magnified two-dimensional images of internal cell structures.

Scanning Electron Microscope (SEM)

Electron microscope that produces detailed three-dimensional images of a specimen’s surface.

Plasma Membrane

Phospholipid bilayer with embedded proteins, cholesterol, and glycolipids that encloses the cell and regulates transport.

Phospholipid Bilayer

Amphipathic double layer of phospholipids forming the basic framework of the plasma membrane.

Cholesterol (in membranes)

Four-ring lipid that stabilizes membrane fluidity and strengthens the bilayer.

Glycolipid

Membrane lipid with attached carbohydrate; contributes to the glycocalyx for cell recognition.

Glycocalyx

Sugary coating of glycoproteins and glycolipids on the cell surface that functions as an identity marker.

Cytosol

Viscous intracellular fluid containing water, ions, and dissolved macromolecules.

Organelle

Specialized cellular structure with a specific function; may be membrane-bound or non-membrane-bound.

Membrane-Bound Organelle

Organelle surrounded by its own membrane, e.g., ER, Golgi, lysosome, mitochondrion.

Non-Membrane-Bound Organelle

Protein-based organelle lacking a surrounding membrane, e.g., ribosome, centrosome, proteasome.

Inclusion

Temporary cytoplasmic storage structure such as pigments, glycogen, or lipid droplets.

Nucleus

Largest cellular structure that houses DNA and contains the nucleolus.

Cilia

Short, hair-like plasma-membrane extensions that move substances across the cell surface.

Flagellum

Long, whip-like projection that propels an entire cell; sperm tail is an example.

Microvilli

Thin plasma-membrane folds that increase surface area for absorption.

Transport Protein

Membrane protein (channel, carrier, or pump) that regulates movement of substances across the membrane.

Cell-Surface Receptor

Membrane protein that binds specific ligands to initiate a cellular response.

Identity Marker

Glycoprotein or glycolipid that communicates a cell’s identity to the immune system.

Anchoring Site

Membrane protein that secures the cytoskeleton to the plasma membrane.

Cell-Adhesion Protein

Membrane protein that forms cell-to-cell attachments.

Passive Transport

Membrane transport that requires no ATP and moves substances down their concentration gradient.

Active Transport

ATP-dependent movement of a substance against its concentration gradient.

Simple Diffusion

Unassisted movement of small nonpolar molecules directly through the phospholipid bilayer.

Facilitated Diffusion

Passive transport of polar or charged molecules via membrane proteins (channels or carriers).

Channel-Mediated Diffusion

Ion movement through a water-filled protein channel; may be leak or gated.

Carrier-Mediated Diffusion

Transport of small polar molecules by a carrier protein that changes shape.

Osmosis

Passive movement of water across a semipermeable membrane in response to solute concentration differences.

Isotonic Solution

Extracellular fluid with the same solute concentration as cytosol; no net water movement.

Hypotonic Solution

Solution with lower solute concentration than cytosol; causes cell swelling or lysis.

Hypertonic Solution

Solution with higher solute concentration than cytosol; causes cell shrinkage (crenation).

Primary Active Transport

Pump-mediated transport that directly uses ATP hydrolysis, e.g., Na⁺/K⁺ pump.

Secondary Active Transport

Coupled transport using energy from another substance moving down its gradient; includes symporters and antiporters.

Symporter

Membrane protein that moves two substances in the same direction across the membrane.

Antiporter

Membrane protein that moves two substances in opposite directions.

Vesicular Transport

ATP-requiring bulk movement of materials via membrane-bound vesicles.

Exocytosis

Vesicular release of substances from the cell to the extracellular fluid.

Endocytosis

Vesicular uptake of substances into the cell; includes phagocytosis, pinocytosis, receptor-mediated endocytosis.

Phagocytosis

“Cell eating” – ingestion of large particles or cells by vesicle formation.

Pinocytosis

“Cell drinking” – nonspecific uptake of extracellular fluid and dissolved solutes.

Receptor-Mediated Endocytosis

Selective uptake of molecules bound to specific membrane receptors.

Resting Membrane Potential (RMP)

Electrical charge difference across the plasma membrane of a resting cell (≈ –70 mV).

Na⁺/K⁺ Pump

Primary active transport protein exporting 3 Na⁺ and importing 2 K⁺ to maintain gradients and RMP.

Ligand

Signaling molecule that binds to a receptor to initiate a response.

Channel-Linked Receptor

Ligand-gated ion channel that opens or closes upon ligand binding.

Enzymatic Receptor

Membrane receptor with intrinsic kinase activity that phosphorylates intracellular enzymes when activated.

G Protein-Coupled Receptor (GPCR)

Receptor that activates an associated G protein to trigger intracellular signaling cascades.

Endoplasmic Reticulum (ER)

Extensive membranous network; rough ER synthesizes proteins, smooth ER synthesizes lipids and detoxifies.

Golgi Apparatus

Stack of flattened sacs that modifies, sorts, and packages proteins and lipids for secretion or delivery.

Lysosome

Membrane sac containing digestive enzymes for intracellular digestion and autophagy.

Peroxisome

Organelle that carries out β-oxidation, lipid synthesis, and detoxification using oxidative enzymes.

Mitochondrion

Double-membraned “powerhouse” organelle responsible for aerobic ATP production; contains its own DNA.

Ribosome

Non-membranous organelle composed of rRNA and protein that synthesizes polypeptides; can be free or bound.

Centrosome

Microtubule-organizing region containing a pair of centrioles; essential for spindle formation in mitosis.

Cytoskeleton

Network of protein filaments (microfilaments, intermediate filaments, microtubules) providing structure and movement.

Microfilament

Actin filament that supports cell shape and aids in muscle contraction and cell motility.

Intermediate Filament

Stable cytoskeletal fiber providing tensile strength and anchoring organelles.

Microtubule

Hollow tubulin cylinder that forms spindle fibers and guides organelle movement.

Chromatin

Finely filamented DNA-protein complex present when the cell is not dividing.

Chromosome

Tightly coiled DNA visible during cell division; human somatic cells have 46.

Nucleolus

Non-membranous nuclear body that produces ribosomal subunits.

Transcription

Nuclear process where RNA polymerase synthesizes RNA from a DNA template.

Translation

Cytoplasmic process where ribosomes read mRNA codons to assemble amino acids into a protein.

Codon

Three-nucleotide mRNA sequence that specifies a particular amino acid or stop signal.

Anticodon

Three-nucleotide sequence on tRNA complementary to an mRNA codon.

Tight Junction

Row of proteins that seals neighboring cells, preventing passage of substances between them.

Desmosome

Button-like junction with protein plaques and filaments that mechanically bind adjacent cells.

Gap Junction

Connexon-formed tunnel allowing ions and small molecules to pass directly between cells.

Mitosis

Division of a somatic cell nucleus through prophase, metaphase, anaphase, and telophase.

Interphase

Cell-cycle phase (G₁, S, G₂) during which the cell grows and duplicates DNA prior to division.

Apoptosis

Programmed cell death involving orderly dismantling of cellular components without inflammation.