Cell Structure, Membrane Dynamics, and Transport Mechanisms

Vocabulary flashcards covering cell structure, organelles, membrane dynamics, passive and active transport mechanisms, bulk transport, and cell junction types.

Cell Theory

The foundational biological concept stating that all organisms are composed of cells, cells are the smallest living things, and cells arise only from pre-existing cells.

Nucleoid

The region in prokaryotic cells where single circular DNA chromosome is localized without being enclosed by a membrane.

Nucleolus

A specialized region within the eukaryotic nucleus where ribosomal RNA (rRNA) synthesis takes place.

Nuclear Envelope

A double-membrane structure composed of two phospholipid bilayers enclosing the eukaryotic nucleus.

Rough Endoplasmic Reticulum

A region of the endoplasmic reticulum studded with ribosomes that serves as the site for synthesizing proteins destined for secretion, lysosomes, or the plasma membrane.

Smooth Endoplasmic Reticulum

A region of the endoplasmic reticulum lacking bound ribosomes that functions in lipid assembly, membrane synthesis, and $\text{Ca}^{2+}$ storage.

Golgi Apparatus

An organelle consisting of flattened stacks of interconnected membranes with cis and trans faces that packages and distributes molecules synthesized within the cell.

Lysosomes

Trans-Golgi-derived membrane-bound vesicles filled with digestive enzymes that catalyze the breakdown of macromolecules, old organelles, or foreign matter engulfed by phagocytosis.

Peroxisomes

Enzyme-bearing microbodies involved in fatty acid oxidation that produce hydrogen peroxide ($\text{H}_2\text{O}_2$), which is rendered harmless by catalase.

Mitochondria

Bound by two membranes, these eukaryotic organelles contain circular DNA, ribosomes, and cristae to carry out oxidative metabolism to produce ATP.

Cristae

Folds of the inner mitochondrial membrane containing embedded proteins that carry out oxidative metabolism.

Chloroplasts

Three-membrane organelles found in plants, algae, and some protists that contain chlorophyll in thylakoid membranes to convert light energy into sugar.

Stroma

The fluid-filled space within the inner membrane of a chloroplast containing enzymes that fix $\text{CO}_2$ into sugar, along with circular DNA and ribosomes.

Endosymbiosis Theory

The theory proposing that eukaryotic organelles evolved by symbiosis between free-living cells, with mitochondria originating from proteobacteria and chloroplasts from cyanobacteria.

UCYN-A

A newly discovered nitrogen-fixing endosymbiont organelle that resides permanently inside a host marine alga.

Actin Filaments

Cytoskeletal elements composed of two protein chains wound together that enable cellular movements such as contraction, crawling, and pinching.

Microtubules

The largest cytoskeletal fibers, made of \text{\tau}- and \text{\beta}-tubulin dimers, that facilitate cell movement and internal transport of cargo.

Intermediate Filaments

Rope-like cytoskeletal fibers intermediate in size between actin filaments and microtubules that function to stabilize overall cell structure.

Dynein

A motor protein that, together with a connector molecule, transports cargo along microtubules.

Extracellular Matrix

An elaborate mixture of glycoproteins like collagens and hyaluronic acid secreted by animal cells to form a protective layer over the cell surface.

Integrins

Transmembrane proteins that float in the phospholipid bilayer and link the extracellular matrix to the intracellular actin cytoskeleton.

Tenascin-C

An extracellular matrix protein expressed rapidly after muscle injury to reactivate programs needed for muscle regeneration and repair.

Fluid Mosaic Model

A model of cell membrane structure depicting a dynamic, fluid phospholipid bilayer in or on which various globular proteins float laterally.

G-Protein-Coupled Receptor

A major cell-surface receptor family featuring seven transmembrane \text{\tau}-helices that represents the target of roughly one-third of all approved drugs.

$\beta$-barrel

A transmembrane pore created by a cylinder of \text{\beta}-pleated sheets with a polar interior allowing water and small polar molecules to pass through.

Facilitated Diffusion

Passive transport of molecules across a membrane down their concentration gradient assisted by specific channel or carrier proteins.

Aquaporins

Specialized transmembrane channels in the plasma membrane that facilitate the diffusion of water.

Hypertonic Solution

A solution with a higher solute concentration than the cell interior, causing water to diffuse out and animal cells to shrivel.

Hypotonic Solution

A solution with a lower solute concentration than the cell interior, causing water to flow into the cell and create osmotic pressure or cause bursting in animal cells.

Sodium-Potassium Pump

An active transport antiporter that hydrolyzes ATP to export $3\,\text{Na}^+$ ions and import $2\,\text{K}^+$ ions against their concentration gradients.

Uniporters

Selective active transport carrier proteins that move a single molecule at a time across a membrane.

Symporters

Carrier proteins that transport two different molecules across a membrane in the same direction.

Antiporters

Carrier proteins that transport two different molecules across a membrane in opposite directions.

Coupled Transport

An active transport mechanism that uses ATP indirectly by using energy released from one molecule diffusing down its gradient to move another against its gradient.

Phagocytosis

A form of bulk endocytosis in which a cell engulfs solid particulate matter.

Pinocytosis

A form of bulk endocytosis in which a cell takes in extracellular fluid and dissolved substances.

Receptor-Mediated Endocytosis

Bulk transport in which specific target molecules bind to cell-surface receptors localized in clathrin-coated pits before being internalized in coated vesicles.

Exocytosis

Energy-requiring bulk transport process where secretory vesicles fuse with the plasma membrane to release cargo out of the cell.

Exosomes

Extracellular vesicles-in-a-vesicle secreted via exocytosis that mediate intercellular communication using small RNAs, proteins, and lipids.

Tight Junctions

Intercellular connections that link adjacent cell membranes in a tight sheet to prevent leakage between cells.

Desmosomes

Adhesive junctions that mechanically attach the cytoskeletons of neighboring cells or anchor cells to the extracellular matrix.

Gap Junctions

Communicating junctions in animal cells composed of connexons that form channels allowing chemical or electrical signals to pass directly between cells.

Plasmodesmata

Specialized channels through plant cell walls that connect the cytoplasm and smooth ER of adjoining cells.