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Virus

Obligate intracellular parasite that requires a host cell to reproduce and survive; not a cell.

Obligated intracellular parasite

An organism (usually a microbe) that must live and reproduce inside a host cell.

Ubiquitous in nature

Present everywhere; widespread or constantly encountered.

Viral capsid

Protein shell that surrounds and protects the viral genome (DNA or RNA).

Capsomeres

Protein subunits that self-assemble to form the viral capsid.

Enveloped virus

Virus that has a lipid bilayer membrane (envelope) derived from the host cell; contains spikes for attachment.

Naked virus

Virus without an envelope; composed of capsid and genome only; resistant to drying and acids.

Viral envelope

Outer lipid layer derived from host membrane; contains glycoprotein spikes for host recognition.

Spikes (Viral surface proteins)

Glycoproteins that help viruses attach to and enter host cells; determine host range and tissue specificity.

Tissue tropism

The specific tissues or cells a virus can infect, determined by spike-receptor interactions.

Dermatrophic virus

Virus that infects skin tissue.

Neurotrophic virus

Virus that infects nerve tissue.

Viscerotropic virus

Virus that infects internal organs.

Pneumotropic virus

Virus that infects respiratory tissues or lungs.

Cytopathic effect (CPE)

Virus-induced damage that alters cell appearance, often causing death; includes inclusion bodies and syncytia.

Inclusion bodies

Clumps of viral particles or damaged cell organelles seen in infected cells.

Syncytia

Giant multinucleated cells formed when infected cells fuse together.

Lytic infection

Bacteriophage life cycle where the virus replicates and lyses (destroys) the host cell.

Lysogenic infection

Bacteriophage life cycle where viral DNA integrates into the host chromosome and lies dormant as a prophage.

Prophage

Dormant phage DNA integrated into the bacterial chromosome during lysogeny.

Induction (viral)

Trigger that causes a lysogenic phage to enter the lytic cycle, often due to stress (UV light, chemicals).

Adsorption (viral cycle)

Virus binds to host cell surface receptors.

Penetration

Virus enters host cell and releases genome.

Synthesis

Virus replicates its genome and produces proteins.

Assembly

New viral particles are built from synthesized components.

Release

Virus exits host cell, often killing it; occurs by lysis (naked) or budding (enveloped).

Persistent infection

Infection where virus remains in host for a long time, sometimes reactivating periodically.

Provirus

Viral DNA integrated into a host cell's DNA, remaining dormant until activated.

Viroid

Small, naked RNA molecule that infects plants; lacks a protein coat.

Prion

Infectious protein particle that causes fatal neurological diseases like mad cow disease.

Transmissible Spongiform Encephalopathy (TSE)

Group of fatal prion diseases that create sponge-like holes in the brain.

Bacteriophage

Virus that infects and replicates within bacteria.

Embryonated egg culture

Method of growing viruses in fertilized chicken eggs, used in vaccine production.

Cell culture

Laboratory growth of animal cells used to propagate viruses for research or diagnosis.

Plaque (virus culture)

Clear area in a bacterial lawn where viruses have lysed host cells.

Antiviral drugs difficulty

Hard to design because viruses use host cell machinery; drugs risk harming host cells too.

DRACO

Experimental antiviral that triggers death of infected cells by recognizing viral RNA; not approved for humans.

Oncovirus

Virus that can cause cancer by disrupting normal cell growth (e.g., HPV).

Essential nutrients

Substances a cell must take in to survive and grow.

Macronutrients

Needed in large amounts for cell structure and metabolism (C, H, O, N, P, S, K, Mg, Ca, Fe).

Micronutrients

Needed in small amounts; act as enzyme helpers (Mn, Zn, Co, Mo, Cu, Ni).

Organic compounds

Contain carbon and hydrogen; include proteins, nucleic acids, carbohydrates, and lipids.

Inorganic compounds

Do not contain carbon-hydrogen bonds; include water and minerals.

Photoautotroph

Uses sunlight for energy and CO₂ for carbon (photosynthesis).

Chemoautotroph

Uses inorganic compounds (like H₂, S, or Fe) for energy and CO₂ for carbon.

Photoheterotroph

Uses sunlight for energy but gets carbon from organic compounds.

Chemoheterotroph

Gains both carbon and energy from organic sources (protozoa, fungi, animals, many bacteria).

Saprobe

Feeds on dead or decaying organic matter. Example: Fungi.

Parasite

Lives on or in a host and harms it while gaining nutrients. Example: Helminths.

Diffusion

Movement of molecules from high to low concentration until evenly distributed.

Osmosis

Diffusion of water through a selectively permeable membrane.

Isotonic solution

Equal water concentration inside and outside the cell; no net water movement.

Hypotonic solution

Water enters the cell; may cause it to swell and burst.

Hypertonic solution

Water leaves the cell; cell shrinks and becomes distorted.

Simple diffusion

Passive movement of molecules without carrier proteins.

Facilitated diffusion

Passive movement through a protein carrier or channel.

Active transport

Movement of molecules against a gradient using energy (ATP).

Carrier-mediated active transport

Uses transport proteins and ATP to move materials into/out of the cell.

Psychrophile

Grows best at cold temperatures (-5°C to 15°C).

Psychrotolerant

Can grow at 0°C but prefers moderate temperatures (20-40°C).

Mesophile

Grows best at moderate temperatures (20°C-40°C); includes most human pathogens.

Thermophile

Grows best at high temperatures (45°C-80°C).

Extreme thermophile (hyperthermophile)

Grows at extremely high temperatures (80°C-122°C).

Aerobe

Organism that requires oxygen to survive.

Obligate aerobe

Must have oxygen to live.

Microaerophile

Requires small amounts of oxygen (around 5%).

Anaerobe

Does not use oxygen; may die in its presence.

Facultative anaerobe

Can grow with or without oxygen.

Obligate anaerobe

Cannot survive in oxygen.

Capnophile

Requires increased carbon dioxide (5-10%) for growth.

pH tolerance

Most microbes grow best between pH 6-8.

Radiation tolerance

Some microbes can resist or repair damage from UV, X-rays, or other radiation.

Osmotic pressure

Pressure caused by differences in solute concentration across a membrane.

Osmophile

Microbe adapted to high solute (hypertonic) environments.

Halophile

Requires or tolerates high salt concentrations.

Symbiosis

Close nutritional relationship between organisms; at least one depends on the other.

Mutualism

Both organisms benefit. Example: Gut microbiome.

Commensalism

One benefits, the other is unaffected. Example: Staphylococcus epidermidis on skin.

Parasitism

One benefits (parasite), the other is harmed (host). Example: Pathogens.

Synergism

Cooperative interaction where both benefit but relationship is not required. Example: Gut microbes sharing nutrients.

Antagonism

One organism inhibits or kills another. Example: Penicillin-producing molds inhibit bacteria.

Binary fission

Asexual reproduction process where one bacterial cell divides into two identical cells.

Doubling time (generation time)

Time required for a population to double in number.

Lag phase

Period of adjustment before bacteria begin rapid growth.

Log (exponential) phase

Period of maximum growth and cell division.

Stationary phase

Growth slows; cell death equals new cell formation.

Death phase

Cells die faster than new ones are produced.

Spectrophotometer

Instrument that measures cloudiness of culture to estimate cell number.

Staining techniques

Qualitative method to identify bacteria (e.g., Gram staining for cell wall type).

Metabolism

The sum of all chemical reactions that occur within a cell to maintain life.

Catabolism

Breakdown of larger molecules into smaller ones; releases energy.

Anabolism

Building of larger molecules from smaller ones; requires energy.

Enzyme

Protein that acts as a catalyst to speed up chemical reactions without being consumed.

Substrate

The specific molecule an enzyme acts upon.

Active site

Region on an enzyme where the substrate binds and the reaction occurs.

Apoenzyme

The protein portion of an enzyme without its cofactor; inactive alone.

Holoenzyme

A complete, active enzyme with its cofactor or coenzyme attached.

Cofactor

Inorganic element (like metal ions) required for enzyme function.

Coenzyme

Organic molecule (often a vitamin) that helps enzymes function.

Enzyme regulation

The control of enzyme production or activity to match cell needs.