Cell Organization, Cytoskeleton, Membranes & Cellular Processes

A comprehensive set of vocabulary flashcards covering cell architecture, microscopy, cytoskeletal elements, membranes, transport mechanisms, cell cycle, and pathology discussed in the lecture.

Cytoplasm

The portion of the cell outside the nucleus, composed of cytosol, organelles, cytoskeleton, and inclusions.

Cytosol

The aqueous fluid component of cytoplasm that contains ions, metabolites, and soluble proteins.

Cytoplasmic Matrix

The gel-like network of solutes and microtrabecular strands that suspends organelles within the cytosol.

Organelles

Specialized, membrane-bound structures that perform distinct cellular functions (e.g., ER, mitochondria).

Inclusions

Non-living cytoplasmic or nuclear deposits such as lipofuscin, glycogen, or lipid droplets.

Cytoskeleton

Dynamic network of microtubules, actin filaments, and intermediate filaments that supports cell shape and movement.

Microtubule

A 25-nm hollow tube of α- and β-tubulin dimers involved in transport, cell division, and ciliary motion.

Intermediate Filament

A 8–10 nm rope-like filament providing tensile strength; includes keratins, vimentin, neurofilaments, etc.

Actin Filament (Microfilament)

A 6–8 nm helical polymer of G-actin that supports cell cortex, motility, and muscle contraction.

Microtrabecular Network

Fine protein lattice revealed by HVEM that links cytoskeletal elements within cytoplasm.

Nucleus

Largest organelle; stores the genome and houses DNA/RNA synthesis machinery.

Nucleolus

Dense, non-membranous nuclear region where rRNA transcription and ribosome assembly occur.

Chromatin

Complex of DNA with histone and non-histone proteins, organized as heterochromatin or euchromatin.

Heterochromatin

Densely packed, transcriptionally inactive chromatin that stains dark with hematoxylin.

Euchromatin

Lightly packed, transcriptionally active chromatin appearing pale in light microscopy.

Constitutive Heterochromatin

Permanently inactive, repetitive DNA regions found in identical positions on chromosomes.

Facultative Heterochromatin

Chromatin that can switch between active and inactive states, e.g., Barr body.

Barr Body

Condensed, inactive X chromosome seen as a heterochromatic drumstick in female nuclei.

Nucleosome

Basic chromatin unit: ~147 bp DNA wrapped around an octamer of core histones.

Nuclear Envelope

Double membrane surrounding nucleus; outer layer continuous with rough ER.

Nuclear Pore Complex

Large protein channel spanning the nuclear envelope that regulates nucleocytoplasmic transport.

Perinuclear Cisternal Space

The lumen between inner and outer nuclear membranes.

Light Microscope

Instrument using visible light and glass lenses to magnify specimens up to ~1,000×.

Electron Microscope

Instrument that uses electron beams and electromagnetic lenses for nanometer-scale resolution.

High-Voltage Electron Microscopy (HVEM)

EM technique (0.25–0.5 µm sections) revealing 3-D ultrastructure such as microtrabeculae.

Plasma Membrane

Selective, 7–10 nm lipid-protein bilayer enclosing the cell.

Lipid Bilayer

Two leaflets of amphipathic lipids forming the fundamental membrane structure.

Integral Protein

Membrane protein spanning the bilayer; functions as channel, pump, receptor, etc.

Peripheral Protein

Protein loosely attached to membrane surface; often enzymatic or cytoskeletal.

Glycocalyx

Extracellular carbohydrate coat formed by glycoproteins and glycolipids; mediates protection and recognition.

Phospholipid

Major membrane lipid with hydrophilic phosphate head and hydrophobic fatty acid tails.

Sphingolipid

Membrane lipid built on a sphingosine backbone; includes sphingomyelin and glycosphingolipids.

Cholesterol

Sterol intercalated within membranes that buffers fluidity and stabilizes bilayer.

Rough Endoplasmic Reticulum (RER)

ER region studded with ribosomes; synthesizes secretory and membrane proteins.

Smooth Endoplasmic Reticulum (SER)

Ribosome-free ER involved in lipid synthesis and detoxification.

Golgi Apparatus

Stacked cisternae that modify, sort, and package proteins from the ER.

Lysosome

Acidic, enzyme-rich vesicle that degrades macromolecules and worn organelles.

Hydrolase Enzymes

Acid hydrolases within lysosomes responsible for intracellular digestion.

Mitochondrion

Double-membranous organelle that generates ATP via oxidative phosphorylation.

Cristae

Folded inner mitochondrial membrane increasing surface area for respiratory enzymes.

Peroxisome

Single-membrane organelle containing oxidases and catalase for hydrogen peroxide metabolism.

Catalase

Peroxisomal enzyme that converts H₂O₂ to water and oxygen, protecting cells from oxidative damage.

Microtubule Organizing Center (MTOC)

Cellular region (centrosome) nucleating and anchoring microtubules; contains centrioles.

Centriole

9×3 microtubule triplet cylinder that buds basal bodies and organizes spindle poles.

Basal Body

Centriole-derived structure anchoring the axoneme of a cilium or flagellum.

Kinesin

Plus-end-directed microtubule motor protein moving vesicles toward the cell periphery.

Dynein

Minus-end-directed motor that transports cargo inward and powers ciliary bending.

Tau Protein

Microtubule-stabilizing protein abundant in neurons; hyperphosphorylation linked to Alzheimer’s disease.

Singlet Microtubule

Individual 13-protofilament microtubule found in cytoplasm and mitotic spindle.

Doublet Microtubule

A- and B-tubule pair forming the axoneme of cilia and flagella.

Triplet Microtubule

A-, B-, and C-tubule set found in centrioles and basal bodies.

Keratin

Class 1-2 intermediate filament proteins of epithelial cells providing mechanical resilience.

Vimentin

Class 3 intermediate filament of mesoderm-derived cells such as fibroblasts.

Desmin

Muscle-specific intermediate filament that stabilizes sarcomere alignment.

Neurofilament

Class 4 intermediate filament heteropolymers that strengthen neuronal axons.

Lamins

Class 5 nuclear intermediate filaments forming the nuclear lamina beneath the envelope.

Beaded Filament

Class 6 intermediate filament found in eye lens fibers; composed of filensin and phakinin.

Apoptosis

Programmed cell death featuring caspase activation, DNA fragmentation, and membrane blebbing.

Necrosis

Uncontrolled cell death due to injury, leading to swelling, lysis, and inflammation.

Autophagy

Lysosome-mediated degradation of a cell’s own organelles via autophagosomes.

Diffusion

Passive movement of molecules down their concentration gradient through the lipid bilayer.

Facilitated Diffusion

Carrier- or channel-mediated passive transport of solutes down a gradient.

Uniport

Transport system that moves a single solute in either direction across a membrane.

Symport

Coupled transporter that moves two solutes in the same direction (co-transport).

Antiport

Coupled transporter exchanging two solutes in opposite directions (counter-transport).

Primary Active Transport

Pump-mediated solute movement against a gradient driven directly by ATP hydrolysis.

Secondary Active Transport

Transport that uses the energy of an ion gradient established by primary pumps.

Sodium–Potassium Pump

Na⁺/K⁺-ATPase that expels 3 Na⁺ and imports 2 K⁺ per ATP, maintaining membrane potential.

Aquaporin

Tetrameric water channel that permits rapid, selective water movement but excludes ions.

Pinocytosis

Continuous, non-specific “cell drinking” of extracellular fluid via small vesicles.

Phagocytosis

Actin-dependent engulfment of large particles into phagosomes by specialized cells.

Receptor-Mediated Endocytosis

Selective uptake of ligands via clathrin-coated pits and vesicles.

Clathrin

Triskelion protein forming coated pits/vesicles for receptor-mediated endocytosis.

Caveolae

Flask-shaped, clathrin-independent invaginations rich in caveolin; involved in lipid and signal uptake.

Dynamin

GTPase that pinches off clathrin- or caveolae-coated vesicles from the plasma membrane.

Exocytosis

Fusion of intracellular vesicles with the plasma membrane to release contents outside the cell.

Constitutive Secretory Pathway

Continuous exocytosis supplying membrane and extracellular matrix without external signal.

Regulated Secretory Pathway

Signal-triggered exocytosis from storage granules in endocrine, exocrine, or neural cells.

SNARE Proteins

v- and t-SNARE pairs that mediate vesicle docking and membrane fusion during exocytosis.

Rab GTPase

Vesicle surface GTP-binding protein that guides targeting and docking to specific membranes.

Kartagener Syndrome

Hereditary dynein defect causing immotile cilia, chronic respiratory infections, and situs inversus.

Gaucher Disease

Lysosomal storage disorder due to glucocerebrosidase deficiency leading to lipid buildup.

Lysosomal Storage Disease (LSD)

Group of disorders where absent lysosomal enzymes cause accumulation of undegraded substrates.

Cell Cycle

Ordered series of phases (G₁, S, G₂, M) culminating in cell division.

Restriction Checkpoint

G₁ control point assessing size, nutrients, and DNA integrity before S phase entry.

Mitotic Spindle

Microtubule apparatus that segregates chromosomes during mitosis.

Metaphase

Mitotic stage where chromosomes align on the equatorial plate attached to spindle fibers.

Anaphase

Stage of mitosis when sister chromatids separate and move to opposite spindle poles.

Cytokinesis

Actin-myosin ring–mediated division of cytoplasm producing two daughter cells.

Spindle-Assembly Checkpoint

M-phase control ensuring all chromosomes are attached before anaphase onset.