Virology, Prokaryotic & Eukaryotic Cell Biology – Key Vocabulary

Comprehensive vocabulary cards covering fundamental virology, bacteriology, cell structure, and microbial genetics concepts from the lecture notes.

Virus

Obligate intracellular infectious particle composed of nucleic acid (DNA or RNA) surrounded by a protein coat; inert outside host cells.

Virion

A complete, fully assembled viral particle able to infect a host cell.

Host Range

The spectrum of host species or cell types a virus can infect; determined by specific receptor interactions and cellular factors.

Bacteriophage (Phage)

A virus that specifically infects bacteria.

Nucleic Acid (viral)

Either DNA or RNA, single- or double-stranded, never both in the same virion.

Capsid

Protein coat surrounding viral nucleic acid; protects genome and aids attachment/penetration.

Capsomere

Protein subunit that assembles to form the viral capsid.

Envelope (virus)

Lipid-protein-carbohydrate layer derived from host membrane that surrounds some viruses.

Spikes

Glycoprotein projections on viral envelopes used for attachment; antigenic determinants.

Antigenic Drift

Minor, gradual mutations in viral surface antigens that alter antibody recognition.

Antigenic Shift

Major, abrupt change in surface antigens, producing novel viral strains (e.g., influenza).

Helical Virus

Virus whose capsid proteins wind around nucleic acid to form a hollow rod; e.g., rabies, Ebola.

Icosahedral Virus

Virus with symmetrical capsid of 20 triangular faces and 12 corners; e.g., poliovirus.

Complex Virus

Virus with complicated structures beyond simple capsid, such as tails and baseplates; e.g., bacteriophage.

Retrovirus

RNA virus that carries reverse transcriptase to synthesize DNA from RNA; includes HIV.

Reverse Transcriptase

Viral enzyme that converts RNA into complementary DNA (cDNA).

Provirus

Viral DNA integrated into host genome; may remain latent or direct active infection.

Attachment (viral)

First step of viral replication: specific binding of virion proteins to host cell receptors.

Penetration (viral)

Entry of virion or genome into host cell via endocytosis or membrane fusion.

Uncoating

Separation of viral nucleic acid from capsid within host cell.

Assembly (viral)

Stage where viral genomes and proteins self-assemble into new virions.

Release (viral)

Exit of mature virions by budding (enveloped) or lysis (non-enveloped).

Cytopathic Effect (CPE)

Visible cellular damage caused by viral infection (e.g., inclusion bodies, syncytia).

Inclusion Body

Aggregates of viral particles or altered organelles seen in infected cells.

Syncytium

Multinucleated giant cell formed by fusion of infected cells; characteristic of RSV, HIV.

Persistent Infection

Slow, continuous production of virus over long periods without rapid cell death.

Chronic Latent Infection

Virus remains dormant for years with periodic reactivation; e.g., HSV, Varicella-Zoster.

Oncogenic Virus

Virus capable of transforming host cells and inducing tumors.

Oncogene

Normal cellular gene that can be activated to promote uncontrolled growth.

Temperate Phage

Bacteriophage able to choose between lytic and lysogenic cycles.

Prophage

Phage genome integrated into bacterial chromosome during lysogeny.

Lysogenic Conversion

Acquisition of new bacterial traits (e.g., toxin production) due to prophage genes.

Plaque Assay

Method to quantify viruses by counting clear zones (plaques) on a lawn of host cells.

Prion

Infectious protein lacking nucleic acid; causes transmissible spongiform encephalopathies.

Viroid

Small, circular piece of naked RNA that infects plants; no protein coat.

Flagellum (bacterial)

Long, helical appendage providing motility; built of flagellin protein.

Monotrichous

Single flagellum at one pole of bacterium.

Lophotrichous

Cluster of flagella at one pole.

Amphitrichous

Single flagellum (or tuft) at both poles.

Peritrichous

Flagella distributed over entire cell surface.

Periplasmic Flagella

Internal flagella wrapped around spirochetes, producing corkscrew motility.

Chemotaxis

Directed bacterial movement toward attractants or away from repellents.

Run-and-Tumble

Pattern of straight swimming (run) interrupted by random reorientation (tumble).

Fimbriae

Short, numerous protein appendages for adhesion to surfaces and cells.

Pilus (Pili)

Longer protein appendage; includes sex pilus used for conjugative DNA transfer.

Glycocalyx

External polysaccharide/protein coating of bacteria; includes capsules and slime layers.

Capsule

Organized, firmly attached glycocalyx enhancing virulence and resisting phagocytosis.

Slime Layer

Loose, unorganized glycocalyx aiding surface attachment and biofilm formation.

Biofilm

Complex microbial community embedded in self-produced matrix adhering to surfaces.

Peptidoglycan

Mesh-like polymer of NAG-NAM sugars cross-linked by peptides; main component of bacterial cell walls.

Teichoic Acid

Acidic polysaccharide embedded in Gram-positive cell walls; aids ion transport and serotyping.

Lipopolysaccharide (LPS)

Outer membrane molecule of Gram-negative bacteria composed of Lipid A, core, and O antigen.

Lipid A

Toxic endotoxin component of LPS responsible for fever and shock.

O Antigen

Polysaccharide portion of LPS used to serotype Gram-negative bacteria.

Outer Membrane

Additional lipid bilayer outside peptidoglycan of Gram-negative bacteria; contains LPS and porins.

Porin

Protein channel in Gram-negative outer membrane that permits small molecules to pass.

Mycolic Acid

Waxy, long-chain fatty acid in cell walls of Mycobacterium; basis of acid-fast staining.

Mycoplasma

Bacteria lacking a cell wall; membrane contains sterols for stability.

L-Form

Cell-wall-deficient variant of bacteria produced by mutation or antibiotic exposure.

Gram Stain

Differential stain separating bacteria into Gram-positive (purple) and Gram-negative (pink) based on cell wall structure.

Plasma Membrane (bacterial)

Phospholipid bilayer lacking sterols; site of ATP production and transport.

Nucleoid

Region of prokaryotic cytoplasm containing circular chromosome without nuclear membrane.

Plasmid

Small, extrachromosomal circular DNA carrying non-essential but advantageous genes.

Ribosome 70S

Prokaryotic ribosome (50S + 30S) where protein synthesis occurs; target of many antibiotics.

Inclusion Body (Bacterial)

Reserve deposit of nutrients such as glycogen, poly-β-hydroxybutyrate, or volutin.

Endospore

Highly resistant, dormant structure formed by Bacillus, Clostridium, and Sporosarcina under stress.

Sporulation

Process of endospore formation inside vegetative bacterial cell.

Germination (spore)

Return of a dormant endospore to active vegetative growth under favorable conditions.

Actin Cytoskeleton (bacterial)

Network of actin-like proteins that helps maintain rod and spiral bacterial shapes.

Binary Fission

Asexual reproduction method by which one prokaryotic cell divides into two daughter cells.

Coccus

Spherical bacterial shape.

Bacillus (shape)

Rod-shaped bacterium.

Vibrio

Comma-shaped curved rod bacterium.

Spirillum

Rigid, helical bacterium with external flagella.

Spirochete

Flexible, corkscrew bacterium with periplasmic flagella.

Strepto-

Prefix denoting chain arrangement of bacterial cells (e.g., streptococci).

Staphylo-

Prefix denoting grape-like cluster arrangement (e.g., staphylococci).

Palisade

Side-by-side arrangement of bacilli resembling a picket fence.

Endosymbiont Theory

Idea that mitochondria and chloroplasts originated from engulfed prokaryotes living symbiotically inside early eukaryotic cells.

70S Ribosome (organelle)

Prokaryote-type ribosome found inside mitochondria and chloroplasts of eukaryotes.

Eukaryote

Cell type with membrane-bound nucleus and organelles; includes fungi, protists, plants, animals.

Prokaryote

Cell type lacking membrane-bound nucleus and organelles; includes Bacteria and Archaea.

Mitosis

Eukaryotic process of nuclear division producing genetically identical daughter cells.

Binary Fission

Primary prokaryotic cell division process producing two identical cells.

Smooth Endoplasmic Reticulum

Eukaryotic organelle involved in lipid synthesis and detoxification.

Rough Endoplasmic Reticulum

ER studded with ribosomes where secretory and membrane proteins are synthesized.

Golgi Apparatus

Eukaryotic organelle that modifies, packages, and ships proteins and lipids.

Lysosome

Eukaryotic vesicle containing hydrolytic enzymes for intracellular digestion.

Mitochondrion

Organelle where aerobic respiration produces most cellular ATP.

Chloroplast

Photosynthetic organelle in plants and algae that converts light energy to chemical energy.

Cilia

Short, numerous eukaryotic appendages with 9 + 2 microtubule pattern; used for motility and feeding.

Eukaryotic Flagellum

Long motility appendage with 9 + 2 microtubule arrangement; moves by undulation.

Chitin

Polysaccharide forming fungal cell walls and arthropod exoskeletons.

Teichoic Acid

Negatively charged polymer in Gram-positive walls aiding ion passage and identification.

Lipoteichoic Acid

Teichoic acid linked to plasma membrane lipids in Gram-positive bacteria.

Acid-Fast Bacterium

Bacterium with waxy mycolic acids in wall that resists decolorization by acid alcohol; e.g., Mycobacterium.

Prion Diseases

Neurodegenerative disorders like Creutzfeldt-Jakob disease, kuru, scrapie, caused by misfolded prion protein.

Endotoxic Shock

Severe inflammatory response and vascular collapse due to release of Gram-negative Lipid A.

Group Translocation

Type of active transport in bacteria where substance is chemically modified during uptake (e.g., PTS for glucose).

Conjugation

Bacterial DNA transfer mediated by sex pilus between donor and recipient cells.