Cell Structure – Vocabulary Flashcards

A comprehensive set of vocabulary flashcards covering major terms and concepts from the Cell Structure lecture notes.

Organelle

Metabolically active, membrane-bound (or specialized) structure that carries out a specific function inside a cell.

Nucleus

Largest organelle; centrally located, double-membrane bound structure that stores almost all DNA and conducts RNA synthesis and ribosome assembly.

Chromatin

DNA double helix wrapped around histone nucleosomes; exists as euchromatin (loose, active) or heterochromatin (condensed, inactive).

Nucleosome

‘Bead’ of chromatin composed of DNA wound around a core of histone proteins, stabilizing DNA packaging.

Euchromatin

Light-staining, loosely packed, transcriptionally active chromatin found toward the nuclear interior.

Heterochromatin

Dark-staining, densely packed, transcriptionally inactive chromatin typically located near the nuclear periphery.

Nucleolus

Non-membrane bound, dark region in the nucleus where rRNA synthesis and assembly of ribosomal subunits occur.

Nuclear Envelope

Double membrane surrounding the nucleus; perforated by nuclear pores that regulate traffic between nucleus and cytoplasm.

Nuclear Pore

Large protein channel in the nuclear envelope that permits passage of RNA, ribosomal subunits, and proteins.

Importin

Transport protein that carries cargo from the cytoplasm into the nucleus through nuclear pores.

Exportin

Transport protein that mediates movement of RNA or proteins from the nucleus to the cytoplasm.

Ribosome

Complex of rRNA and proteins composed of large and small subunits that translates mRNA into polypeptides.

Polysome

Cluster of multiple ribosomes simultaneously translating the same mRNA strand.

Rough Endoplasmic Reticulum (RER)

Membrane network studded with ribosomes; synthesizes proteins destined for secretion or insertion into membranes.

Signal Recognition Particle (SRP)

Ribonucleoprotein that binds N-terminal signal sequences and directs translating ribosomes to the RER surface.

Golgi Apparatus

Stack of flattened cisternae (cis, medial, trans) that modifies, sorts, packages, and dispatches RER-derived proteins.

Cis-Golgi Face

Golgi cisterna closest to the ER that receives COPII vesicles from ERGIC.

Trans-Golgi Face

Golgi cisterna closest to the plasma membrane; generates vesicles for final protein destinations.

ER-Golgi Intermediate Complex (ERGIC)

Transitional compartment between ER and cis-Golgi where COPII vesicles first fuse.

COPII Coat Protein

Protein coat on vesicles budding from ER to ERGIC, aiding vesicle formation and targeting.

COPI Coat Protein

Protein coat on vesicles moving retrograde or between Golgi cisternae (cis → medial → trans).

Clathrin

Triskelion protein forming polyhedral coats on vesicles leaving trans-Golgi or involved in endocytosis at the plasma membrane.

Clathrin-Coated Pit

Invagination of the plasma membrane lined intracellularly with Clathrin that buds to form endocytic vesicles.

Exocytosis

Vesicle-mediated fusion with the plasma membrane to release or insert proteins outside the cell.

Endocytosis

Uptake of extracellular molecules via vesicle formation; includes receptor-mediated pinocytosis leading to endosomes and lysosomes.

Pinocytotic Vesicle

Small vesicle created during receptor-mediated endocytosis that internalizes extracellular fluid and ligands.

Early Endosome (CURL)

Acidic (pH 6) compartment near plasma membrane where receptors and ligands uncouple and receptors recycle.

Late Endosome

Endocytic compartment deeper in cytoplasm (near Golgi) that transfers cargo to lysosomes for degradation.

Lysosome

Acidic (pH 5) digestive organelle containing hydrolytic enzymes (proteases, lipases, sulfatases) that break down endocytosed material.

Proton Pump

Membrane protein that uses ATP to transport H⁺ into lysosomes or other organelles, lowering internal pH.

Mitochondrion

Rod-shaped, double-membrane organelle that generates ATP via oxidative phosphorylation; contains its own DNA.

Crista

Fold of the inner mitochondrial membrane that increases surface area for oxidative phosphorylation complexes.

Porin

Large channel protein in the outer mitochondrial membrane allowing passage of most small molecules.

Cardiolipin

Four-tailed phospholipid unique to the inner mitochondrial membrane, making it highly impermeable to ions.

ATP Synthase

Large inner-membrane enzyme that synthesizes ATP as H⁺ flows back into the mitochondrial matrix.

Respiratory Complex (Electron Transport Chain)

Series of inner-membrane protein complexes that pump protons into the intermembrane space, generating the proton gradient.

Matrix Space

Large interior compartment of mitochondria containing enzymes of the Krebs cycle and mitochondrial DNA.

Intermembrane Space

Region between outer and inner mitochondrial membranes; accumulates protons during electron transport.

Cytoskeleton

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

Microtubule

Hollow, polarized cylinder of 13 protofilaments (α-β tubulin dimers) providing tracks for organelle and vesicle trafficking.

Microtubule Organizing Center (MTOC) / Centrosome

Region near the nucleus containing a pair of centrioles that nucleates and anchors microtubule minus ends.

Centriole

Short cylinder of modified microtubules arranged at right angles within the centrosome; duplicates before mitosis.

Actin Filament (F-Actin)

Helical polymer of G-actin subunits forming a cortical network under the plasma membrane, generating tension and cell movement.

G-Actin

Globular actin monomer that polymerizes (ATP-dependent) to form F-actin filaments.

Myosin

Motor protein family that binds actin; powers contraction and vesicle transport by sliding actin filaments.

Intermediate Filament

Rope-like cytoskeletal fibers that provide tensile strength and mechanical stability to cells and tissues.

Cellular Tensegrity

Model describing how cytoskeletal elements balance compressive (microtubules) and tensile (actin) forces to stabilize cell shape.