Cell Biology, Membrane Transport, and Cell Communication

Vocabulary flashcards covering cell structure, organelles, plasma membrane properties, passive and active transport mechanisms, and cellular communication signaling pathways.

Cell Theory

The fundamental biological principle stating that all living organisms are composed of cells and that all cells arise from pre-existing cells.

Prokaryotic Cell

A cell category characterized by the absence of a membrane-bound nucleus and membrane-bound organelles, containing a nucleoid region where its DNA is located.

Eukaryotic Cell

A cell category characterized by containing a membrane-bound nucleus and membrane-bound organelles, typically larger in size than prokaryotes.

Nucleoid

The non-membrane-enclosed region in a prokaryotic cell where the cellular DNA is located.

Plasma Membrane

A semi-permeable phospholipid bilayer that bounds the cell, acting as a selective barrier for oxygen, nutrients, and waste.

Nucleus

The largest organelle in a eukaryotic cell that contains genetic material (DNA) bound in bundles called chromosomes.

Nuclear Envelope

A phospholipid bilayer membrane with nuclear pores that encloses the nucleus, separating it from the cytoplasm and selectively transporting molecules.

Nucleolus

A structure located within the nucleus responsible for manufacturing ribosomes.

Ribosome

A cellular organelle, found free-floating or attached to the endoplasmic reticulum, that serves as the site of protein synthesis by linking amino acids into polypeptide chains.

Mitochondrion

A double-membrane organelle that acts as the site of cellular respiration and $\text{ATP}$ production.

Rough Endoplasmic Reticulum

A portion of the endoplasmic reticulum studded with ribosomes that produces proteins for secretion, membrane insertion, and glycoprotein synthesis.

Smooth Endoplasmic Reticulum

A portion of the endoplasmic reticulum lacking ribosomes that functions in lipid synthesis, carbohydrate metabolism, drug detoxification, and calcium storage.

Golgi Apparatus

An organelle consisting of flattened membranous sacs (cisternae) that modifies, sorts, and repackages cellular products into transport vesicles.

Lysosome

A membrane-bound sac containing hydrolytic enzymes that hydrolyzes proteins, fats, polysaccharides, and nucleic acids.

Peroxisome

An organelle responsible for the catabolism of fatty acids and the breakdown of unwanted metabolic byproducts.

Cytoskeleton

A network of fibers—microtubules, microfilaments, and intermediate filaments—that maintains cell shape, anchors organelles, and enables cellular motility.

Microtubules

The thickest fibers of the cytoskeleton, involved in maintaining cell shape, forming cilia and flagella for motility, and organizing spindle poles during division.

Intermediate Filaments

Cytoskeletal fibers of intermediate thickness that provide permanent structural framework to support cell shape and fix organelles in position.

Extracellular Matrix (ECM)

An external meshwork of animal cells composed of glycoproteins like collagen and proteoglycans that plays key roles in support, adhesion, movement, and cell communication.

Central Vacuole

A prominent plant cell organelle bounded by the tonoplast that stores water and cell sap, isolates waste products, and maintains turgor pressure against the cell wall.

Chloroplast

A double-membrane plant organelle containing chlorophyll, thylakoids, grana, and stroma, which utilizes light energy, carbon dioxide, and water to perform photosynthesis.

Plasmodesmata

Membrane-lined channels perforating plant cell walls that connect the cytoplasm of adjacent cells to allow molecule transport and communication.

Cell Wall

A rigid layer outside the plasma membrane composed primarily of cellulose in plants that protects the cell, maintains its shape, and prevents excessive water uptake.

Phospholipid Bilayer

The structural foundation of the cell membrane, consisting of two layers of phospholipids with hydrophilic phosphate heads facing outward and hydrophobic fatty acid tails facing inward.

Cholesterol (in cell membrane)

A lipid embedded within the core of the plasma membrane that provides structural support and modulates membrane stability.

Diffusion

The passive transport process where molecules move down their concentration gradient from an area of higher concentration to lower concentration until equilibrium is reached.

Osmosis

The passive diffusion of free water molecules across a selectively permeable membrane toward a region of higher solute concentration.

Isotonic Solution

A solution in which the solute concentration outside the cell is equal to the solute concentration inside the cell, resulting in no net movement of water.

Hypotonic Solution

A solution with a lower solute concentration than the inside of the cell, causing water to enter the cell and leading to lysis in animal cells or turgidity in plant cells.

Hypertonic Solution

A solution with a higher solute concentration than the inside of the cell, causing water to leave the cell and leading to shriveling in animal cells or plasmolysis in plant cells.

Facilitated Diffusion

A passive transport process that speeds up the movement of specific solutes across the cell membrane down their concentration gradient using channel or carrier proteins without using energy.

Active Transport

The energy-requiring movement of a substance across a cell membrane against its concentration gradient using specific carrier proteins.

Sodium-Potassium Pump

A primary active transport carrier protein that expends $\text{ATP}$ to maintain low internal $\text{Na}^+$ and high internal $\text{K}^+$ concentrations against their electrochemical gradients.

Endocytosis

An active bulk transport mechanism where a cell takes in extracellular substances by engulfing them in vesicles derived from the plasma membrane.

Exocytosis

An active bulk transport mechanism where intracellular secretory vesicles fuse with the plasma membrane to discharge their contents outside the cell.

Autocrine Signaling

A chemical signaling mechanism where a cell secretes signaling molecules that bind to receptors on its own surface, targeting itself.

Paracrine Signaling

A chemical signaling mechanism where a cell secretes signals that diffuse locally through extracellular space to act on nearby target cells.

Endocrine Signaling

A long-distance chemical signaling mechanism where specialized cells secrete hormones into the bloodstream to reach distant target cells.

G-Protein-Coupled Receptor (GPCR)

A cell-surface receptor that, upon binding a signaling molecule, interacts with a heterotrimeric G protein, causing its $\text{α}$ subunit to exchange $\text{GDP}$ for $\text{GTP}$.

Receptor Tyrosine Kinase

An enzyme-linked transmembrane receptor that dimerizes and phosphorylates tyrosine residues upon ligand binding, triggering downstream cellular responses.

Protein Kinase

An enzyme that transfers a phosphate group from $\text{ATP}$ to a protein, regulating protein activity in signal transduction cascades.

Protein Phosphatase

An enzyme that detaches phosphate groups from proteins, inactivating protein kinases and terminating signal transduction cascades.

Quorum Sensing

A population-density-dependent bacterial communication system that uses signaling molecules called autoinducers to regulate gene expression and coordinate group behaviors like biofilm formation.