Cell and Molecular Biology – Modules 1 & 2 Vocabulary

Comprehensive vocabulary covering cell structure, classification, membrane composition, transport mechanisms, and related pathologies from Modules 1 and 2.

Cell Theory

Biological principle stating that the cell is the basic unit of life, all organisms are composed of cells, and cells arise only from pre-existing cells.

Protoplasm

The collective living contents of a cell (nucleoplasm + cytoplasm), excluding the plasma membrane.

Information (Life Criterion)

Genetic coding capacity that enables a cell to synthesize needed molecules and transmit traits to offspring.

Metabolism (Life Criterion)

Totality of chemical reactions occurring in a living cell.

Membrane (Life Criterion)

Selectively permeable barrier that encloses and defines a living cell.

Whittaker’s Five-Kingdom System

1969 classification based on phenotypic complexity and nutrition: Monera, Protista, Plantae, Fungi, Animalia.

Monera

Obsolete kingdom of unicellular prokaryotes (bacteria and cyanobacteria).

Protista

Kingdom of mainly unicellular eukaryotes such as protozoa and algae.

Plantae

Eukaryotic kingdom of multicellular, primarily photosynthetic organisms.

Animalia

Eukaryotic kingdom of multicellular heterotrophs that ingest food.

Fungi

Eukaryotic kingdom of heterotrophs that absorb nutrients; cell walls contain chitin.

Carl Woese

Microbiologist who proposed the three-domain system using rRNA sequences.

Three-Domain System

Molecular classification dividing life into Bacteria, Archaea, and Eukarya.

LUCA

Last Universal Common Ancestor of all current life forms.

rRNA

Ribosomal RNA; universally distributed, functionally constant molecule used in phylogenetic studies.

Molecular Phylogeny

Evolutionary analysis based on molecular data such as DNA or RNA sequences.

Ribosome

Ribonucleoprotein complex (70S in prokaryotes, 80S in eukaryotes) that synthesizes proteins.

Svedberg Unit (S)

Non-additive measure of sedimentation rate (10⁻¹³ s) for particles in centrifugation.

Endosymbiotic Hypothesis

Theory that mitochondria and chloroplasts originated from engulfed prokaryotes.

Eukaryote

Cell type with membrane-bound nucleus and organelles; linear chromosomes and histones.

Prokaryote

Unicellular organism lacking nucleus and organelles; circular, supercoiled DNA.

Histone

Basic protein that packages and organizes eukaryotic chromosomal DNA.

Central Dogma

Flow of genetic information: DNA → RNA → protein.

Intron

Non-coding sequence in eukaryotic genes removed during RNA processing.

Exon

Coding sequence in a gene that remains in mature mRNA.

Poly(A) Tail

50-250 adenine nucleotides added to 3′ end of eukaryotic mRNA for stability and export.

Thiomargarita magnifica

Giant filamentous bacterium up to 9.66 mm long, containing genome copies in membrane-bound pepins.

Virion

Complete virus particle consisting of nucleic acid and protective coat, with or without envelope.

Capsid

Protein coat of a virus, composed of capsomeres.

Viral Envelope

Host-derived lipid bilayer surrounding some viruses, containing viral proteins (e.g., spikes).

Naked Virus

Virus lacking an envelope; generally more resistant to inactivation.

Extremophile

Organism (often Archaea) that thrives in extreme environmental conditions.

Methanogen

Anaerobic archaeon that produces methane as metabolic by-product.

Viroid

Infectious, circular ssRNA lacking protein coat; causes plant diseases.

Prion

Infectious misfolded protein (PrP Sc) lacking nucleic acid.

PrPc

Normal cellular prion protein rich in α-helices.

PrPSc

Pathogenic prion conformation enriched in β-sheets; induces misfolding of PrPc.

Transmissible Spongiform Encephalopathy (TSE)

Group of fatal neurodegenerative diseases caused by prions (e.g., CJD, scrapie).

Surface-to-Volume Ratio

Measure inversely related to size; high ratio in small cells permits efficient exchange.

Plasma Membrane

Selective boundary (phospholipid bilayer + proteins) separating cell from environment.

Fluid Mosaic Model

Singer & Nicolson conception of membranes as dynamic lipid bilayers with mobile proteins.

Phospholipid

Amphipathic lipid with glycerol or sphingosine backbone, two fatty acids, and phosphate group.

Glycerophospholipid

Phospholipid with glycerol backbone (e.g., phosphatidylcholine).

Sphingophospholipid

Phospholipid with sphingosine backbone (e.g., sphingomyelin).

Glycolipid

Lipid containing one or more sugars attached to glycerol or sphingosine backbone.

Sterol

Rigid, ring-structured lipid (e.g., cholesterol) modulating membrane fluidity in eukaryotes.

Hopanoid

Sterol-like pentacyclic lipid in many bacterial membranes.

Cardiolipin

Diphosphatidylglycerol found mainly in inner mitochondrial and bacterial membranes.

Saturated Fatty Acid

Hydrocarbon chain lacking double bonds; packs tightly, decreasing membrane fluidity.

Unsaturated Fatty Acid

Fatty acid with cis double bonds causing kinks that increase membrane fluidity.

Transition Temperature (Tm)

Temperature at which a membrane shifts from gel to fluid state.

Cholesterol (Membrane Role)

Sterol that buffers membrane fluidity—restrains movement at high T, prevents tight packing at low T.

Lipid Raft

Cholesterol- and sphingolipid-rich microdomain in membranes involved in signaling and trafficking.

Caveola

Flask-shaped lipid raft invagination coated with caveolin; functions in endocytosis and signaling.

Liposome

Artificial phospholipid vesicle used to deliver drugs or other molecules to cells.

Stealth Liposome

PEGylated liposome designed to evade immune detection for targeted therapy.

Integral (Intrinsic) Protein

Protein embedded in or spanning the lipid bilayer; often transmembrane.

Peripheral (Extrinsic) Protein

Protein loosely bound to membrane surface or another protein; easily extracted.

Lipid-Anchored Protein

Protein covalently attached to lipids (e.g., GPI-anchored prion).

Glycoprotein

Membrane protein with covalently attached carbohydrate; functions in recognition and signaling.

Aquaporin

Channel protein facilitating rapid water transport across membranes.

Simple Diffusion

Passive movement of molecules directly through lipid bilayer down concentration gradient.

Facilitated Diffusion

Passive transport requiring channel or carrier proteins but no energy input.

Active Transport

Energy-dependent movement of substances against electrochemical gradient via pumps.

Carrier Protein

Transport protein that undergoes conformational change to move solute across membrane.

Channel Protein

Protein forming hydrophilic pore allowing specific molecules or ions to cross; may be gated.

P-type ATPase

Pump that phosphorylates itself during transport cycle (e.g., Na⁺/K⁺ ATPase, Ca²⁺ ATPase).

Proton Pump

P-type ATPase exporting H⁺ to generate electrochemical gradient used for secondary transport.

Calcium Pump

P-type ATPase that maintains low cytosolic Ca²⁺ by pumping it out or into ER.

Sodium–Potassium ATPase

Electrogenic pump exporting 3 Na⁺ and importing 2 K⁺ per ATP hydrolyzed.

Membrane Potential

Voltage difference across a membrane, often generated by ion pumps and leak channels.

Symport

Coupled transport in which two solutes move in the same direction across a membrane.

Antiport

Coupled transport exchanging two solutes in opposite directions across a membrane.

FRAP (Fluorescence Recovery After Photobleaching)

Technique measuring lateral mobility of membrane components by observing fluorescence return after localized bleaching.

Spherocytosis

Hereditary disorder causing spherical RBCs due to membrane protein defects.

Dystrophin

Cytoskeletal protein linking muscle cell membrane to extracellular matrix; absence leads to muscular dystrophy.

Muscular Dystrophy

Group of genetic diseases characterized by progressive muscle weakness from defective dystrophin.

Selective Permeability

Property of membranes that allows some substances to cross more easily than others.

Differential Scanning Calorimetry

Technique determining membrane transition temperature by measuring heat flow.

Caveolin

Membrane protein that binds cholesterol and forms the coat of caveolae.

Lipid Solubility

Measure of a molecule’s partitioning into lipid versus water; higher solubility increases membrane permeability.