Biology 1003 - Unit 3: Biology of the Cell

Comprehensive vocabulary flashcards covering cell theory, prokaryotic and eukaryotic organelles, cytoskeleton dynamics, extracellular matrix, cell junctions, and membrane transport mechanisms from Biology 1003 - Unit 3.

Cell Theory

A foundational biological framework stating three core principles: 1) all living organisms are composed of one or more cells enclosed by a membrane; 2) cells are the fundamental structural and functional units of life; and 3) all cells arise from the division of pre-existing cells.

Surface Area to Volume (SA:V) Ratio

The geometric ratio that constrains cell size ($< \backsim 100\,\mu\text{m}$); as cell diameter increases, cellular volume and metabolic requirements expand much faster than surface area, reducing the efficiency of passive diffusion.

Enterocyte

A columnar epithelial cell of the intestinal lining characterized by apical, finger-like projections called microvilli that substantially increase surface area for rapid nutrient absorption and barrier formation.

Nucleus

A membrane-bound eukaryotic organelle enclosed by a double-layered nuclear envelope with nuclear pores that houses genomic DNA and controls all cellular functions.

Nucleolus

A dense region within the eukaryotic nucleus where ribosomal RNA ($\text{rRNA}$) is transcribed and assembled with proteins into small and large ribosomal subunits.

Chromatin

The complex of genomic DNA wrapped around histone proteins to form nucleosomes and solenoid fibers, existing in an amorphous state until condensing into distinct chromosomes during cell division.

Ribosome

A non-membrane-bound ribonucleoprotein complex responsible for translation (protein synthesis); free ribosomes assemble proteins for intracellular use, whereas rough ER-bound ribosomes produce membrane or secreted proteins.

Rough Endoplasmic Reticulum

A continuous membrane-bound network connected directly to the nuclear envelope and studded with ribosomes on its cytosolic surface, primarily responsible for synthesizing and folding proteins.

Smooth Endoplasmic Reticulum

A continuous, ribosome-free membrane-bound organelle network connected to the nucleus that functions in synthesizing carbohydrates and lipids.

Golgi Apparatus

A continuous membrane-bound organelle that modifies, sorts, and packages proteins, carbohydrates, and lipids into secretory vesicles for exocytosis or delivery to lysosomes.

Lysosome

A membrane-bound vesicle containing acid hydrolases and digestive enzymes that conducts phagocytosis, autophagy of damaged cellular organelles, and degradation of endocytosed macromolecules.

Chloroplast

A double-membrane-bound photosynthetic organelle found in plants and algae that performs oxygenic photosynthesis and contains its own autonomous circular DNA and 70S ribosomes.

Mitochondrion

A double-membrane-bound eukaryotic organelle that carries out oxidative phosphorylation to generate ATP via ATP synthase; contains its own circular DNA genome and 70S ribosomes.

Centrosome

A non-membrane-bound organelle in animal cells containing a pair of microtubule-based centrioles that organizes the mitotic spindle during mitosis and meiosis.

Prokaryote

A unicellular organism ($0.1\text{--}5\,\mu\text{m}$ in diameter) lacking a membrane-enclosed nucleus or membrane-bound organelles, typically possessing a single circular haploid chromosome in a nucleoid region, 70S ribosomes, and a peptidoglycan cell wall.

Eukaryote

A unicellular or multicellular organism ($10\text{--}100\,\mu\text{m}$ in diameter) defined by a membrane-enclosed nucleus, multiple linear chromosomes associated with histones, membrane-bound organelles, and 80S cytosolic ribosomes.

Binary Fission

An asexual reproductive process in prokaryotes involving DNA replication, chromosome segregation, and cytokinesis to produce two genetically identical daughter cells.

Plasmid

A small, circular, extrachromosomal DNA molecule found in prokaryotes and select eukaryotes that replicates independently and often encodes adaptive advantages such as antibiotic or heavy-metal resistance.

Bacterial Capsule

An organized outer polysaccharide or slime layer exterior to the bacterial cell wall that promotes surface adherence, biofilm formation, antibiotic resistance, and evasion of the host immune system.

Pili

Hair-like bacterial surface appendages that mediate host cell attachment, invasion, horizontal gene transfer via conjugation, transformation, and Type IV twitching motility.

Cytoskeleton

A dynamic intracellular protein network composed of actin microfilaments ($7\,\text{nm}$), intermediate filaments ($10\,\text{nm}$), and microtubules ($25\,\text{nm}$) that maintains cell morphology, affords structural stability, and enables intracellular transport and motility.

Actin Filaments (Microfilaments)

Thin ($7\,\text{nm}$) cytoskeletal protein fibers that mediate cell shape changes, cytokinesis, motility, cytoplasmic streaming, muscle contraction alongside myosin, and peripheral transport.

Microtubules

Tubular ($25\,\text{nm}$) cytoskeletal polymers of tubulin that form the structural scaffolding of the cell, construct the mitotic spindle to separate chromosomes, power cilia and flagella, and act as intracellular highways.

Kinesin and Dynein

ATP-dependent motor proteins that transport vesicles and organelles along microtubules; dynein walks toward the minus end and kinesin walks toward the plus end.

Intermediate Filaments

Tough, ropelike ($10\,\text{nm}$) cytoskeletal fibers that provide tensile strength, anchor organelles, distribute mechanical stress, and anchor cells to each other and to the extracellular matrix.

Tight Junction

A cell junction that forms a continuous, watertight seal between adjacent epithelial cell membranes to prevent paracellular fluid and solute passage.

Anchoring Junctions

Mechanical junctions (such as desmosomes, adherens junctions, and integrin-mediated junctions) that link adjacent cells or attach cells to the extracellular matrix to withstand mechanical shear stress.

Gap Junction

An intercellular junction consisting of membrane protein channels that directly connect the cytoplasm of adjacent cells, permitting rapid transport of ions and signaling molecules.

Extracellular Matrix (ECM)

A non-cellular three-dimensional macromolecular network composed of ground substance and protein fibers (collagen, elastin) that provides essential structural support, biochemical signals, and tensile strength to tissues.

Ground Substance

The hydrated, gel-like component of the extracellular matrix made of water-binding proteoglycans that cushions tissues, resists compressive forces, and embeds fibrous proteins.

Integrin

A transmembrane anchoring receptor protein that connects the extracellular matrix (via fibronectin or laminin) to the cell cytoskeleton (actin or intermediate filaments).

Passive Transport

The spontaneous movement of chemical substances across a biological membrane down their concentration gradient without the expenditure of cellular metabolic energy.

Simple Diffusion

The unassisted passive movement of small, non-polar molecules (such as $\text{O}_2$, $\text{CO}_2$, and small lipids) directly through the hydrophobic core of the lipid bilayer down their concentration gradient.

Facilitated Diffusion

The passive transport of polar, charged, or large substances across a cell membrane down their concentration gradient mediated by transmembrane protein channels or carrier proteins without ATP consumption.

Osmosis

The passive net diffusion of water molecules across a semipermeable membrane from a region of lower solute concentration (hypotonic) to a region of higher solute concentration (hypertonic) until dynamic equilibrium is established.

Osmolarity

The physical measurement expressing the total concentration of dissolved solute particles per unit volume of solution.

Hypertonic Solution

A solution possessing a higher solute concentration (lower water concentration) than the intracellular fluid, driving net osmotic water movement out of the cell and causing cellular crenation.

Hypotonic Solution

A solution possessing a lower solute concentration (higher water concentration) than the cytoplasm of a cell, inducing osmotic influx of water that swells the cell and can cause osmotic lysis.

Isotonic Solution

A solution with an identical effective solute concentration to the interior of a cell, producing zero net movement of water across the membrane and maintaining normal cellular volume (e.g., $0.9\%\,\text{NaCl}$).

Aquaporin

A specialized transmembrane channel protein that selectively facilitates the rapid passive diffusion of water molecules across the cell membrane.

Active Transport

The energy-dependent translocation of solute molecules across a biological membrane against their chemical or electrochemical gradient.

Primary Active Transport

A transport mechanism in which carrier proteins hydrolyze ATP directly or utilize electron transfer energy to drive solutes uphill against their electrochemical gradients.

Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ ATPase)

A primary active antiport carrier protein that hydrolyzes $1\,\text{ATP}$ to export $3\,\text{Na}^+$ ions out of the cell while importing $2\,\text{K}^+$ ions into the cell, sustaining critical physiological ion gradients.

Secondary Active Transport

A membrane transport process that moves a solute against its concentration gradient powered by the simultaneous downhill diffusion of another ion (often $\text{Na}^+$) along its electrochemical gradient.

Symport

A coupled secondary active transport process that co-transports two distinct molecules or ions across the membrane simultaneously in the same direction (e.g., Sodium-Glucose Cotransporter, SGLT).

Antiport

A coupled membrane transport mechanism that moves two different molecules or ions across the lipid bilayer in opposite directions simultaneously (e.g., $\text{Na}^+/\text{H}^+$ exchanger).

Chemiosmosis

The passive facilitated diffusion of protons ($\text{H}^+$) down an electrochemical gradient across the inner mitochondrial membrane through ATP synthase to drive ATP synthesis.