Viruses, Bacteria, and Cellular Biology

Comprehensive vocabulary review flashcards covering viral biology, prokaryotic structures, cellular organelles, eukaryotic systems, and membrane transport.

Viruses

Noncellular parasitic entities that cannot be classified as living organisms.

Dmitri Ivanowksi

Scientist who in 1892 discovered that tobacco mosaic disease could be transferred from infected to healthy plants even after passing through a Chamberland-Pasteur filter that removed all bacteria.

Capsid

The outer protein coat that encloses the internal nucleic acid (DNA or RNA) of a virus.

Viral Envelope

An external outer membrane possessed by some viruses, composed of proteins and phospholipids derived from the host cell.

Baltimore Classification

A viral classification scheme that categorizes viruses into seven groups based on their genomic replication pathways and mechanism of forming mRNA.

Bacteriophage

A specialized virus that specifically infects bacterial cells.

Lytic Cycle

A viral reproductive cycle in which the viral genome replicates separately from the host genome, resulting in cell lysis (bursting) to release new progeny.

Lysogenic Cycle

A viral reproductive cycle in which the viral genome incorporates into the host genome as a prophage, which divides with the cell before potentially entering the lytic cycle.

Latency

A condition where viruses hide within host tissues and produce few viral proteins for many years.

Vaccines

Biological preparations containing weakened, dead, or molecular subunits of viruses or bacteria that stimulate the immune system to produce antibodies.

Antivirals

Medications designed to destroy or alter components of a virus directly without harming the cellular components of the host.

Prions

Pathogenic proteins lacking nucleic acids that are irregularly misfolded and induce functional native proteins to misfold into disease-causing conformations.

Viroids

Pathogenic naked RNA molecules lacking a protein coat that infect plant species and cause crop failures.

Bacteria

Unicellular prokaryotic organisms considered to be among the earliest forms of life on Earth.

Nucleoid

The non-membrane-bound cytoplasmic region of a bacterial cell where circular chromosomal DNA is located.

Glycocalyx

An outer, viscous gelatinous bacterial covering that protects the cell from desiccation; when thickened, it forms a protective capsule against the host immune system.

Pili

Hair-like bacterial surface projections that facilitate adhesion to surfaces and mediate contact between cells for horizontal gene transfer.

Bacterial Morphologies

The three primary morphological shapes of bacteria: cocci (spherical), bacilli (rod-shaped), and spiralli (spiral-shaped).

Pathogen

Any disease-causing biological agent.

Historical Bacterial Plagues

Major recorded bacterial outbreaks including the Plague of Athens ($430\,\text{BCE}$, caused by Salmonella enterica), the Bubonic Plague ($541 - 750$, caused by Yersinia pestis), and the Black Death ($1346 - 1361$).

Nitrogen Fixation

The enzymatic conversion of atmospheric nitrogen gas by certain bacteria into biologically accessible forms such as ammonia.

Bioremediation

The biological process of utilizing microorganisms, such as bacteria, to break down and remove pollutants from contaminated environments.

Cell Theory

A foundational biological concept stating: (1) all living organisms are composed of one or more cells, (2) cells are the smallest units of life, and (3) new cells arise only from pre-existing cells through cell division.

Surface-Area-to-Volume Ratio

The physical constraint that requires metabolically active cells to remain microscopic, ensuring the plasma membrane surface area is adequate to exchange nutrients and wastes for a given volume.

Prokaryotic Cells

Cells belonging to domains Bacteria and Archaea that lack a membrane-enclosed nucleus and internal membrane-bound organelles.

Eukaryotic Cells

Cells of domain Eukarya possessing a membrane-delimited nucleus and cellular compartmentalization facilitated by membrane-bound organelles.

Nucleolus

A specialized subregion of the eukaryotic nucleus responsible for synthesizing ribosomal RNA and assembling ribosomal subunits.

Chromatin

The structural complex of DNA molecules and associated proteins found within the eukaryotic nucleus.

Ribosomes

Complexes of ribosomal RNA and proteins found in prokaryotes and eukaryotes that catalyze protein and polypeptide synthesis.

Cytosol

The semi-fluid aqueous region within the plasma membrane positioned outside membrane-bound organelles; the principal site where cellular metabolism occurs.

Microtubules

The largest cytoskeletal elements composed of tubulin subunits forming hollow cylinders; synthesized from the centrosome in animal cells and the nuclear envelope in plants to direct chromosome and vesicle transport.

Intermediate Filaments

Cytoskeletal fibers made of keratin aligned in staggered, ropelike arrays that maintain cellular rigidity and tensile strength without frequent dynamic polymerization or depolymerization.

Actin Filaments (Microfilaments)

The smallest cytoskeletal filaments ($7\,\text{nm}$ diameter) formed from two helical strands of actin monomers that dynamically polymerize and depolymerize to support cell movement and plasma membrane shape.

Rough Endoplasmic Reticulum (RER)

A membranous network studded with ribosomes continuous with the outer nuclear envelope, specializing in protein sorting, initial processing, and vesicular export.

Smooth Endoplasmic Reticulum (SER)

A ribosome-free membranous network involved in lipid synthesis, toxic substance degradation, carbohydrate metabolism, and calcium ion ($Ca^{2+}$) storage and release.

Golgi Apparatus

A cellular organelle consisting of stacked, flattened cisternae with cis and trans faces that sorts, modifies, packages, and routes proteins and lipids into transport or secretory vesicles.

Lysosomes

Membrane-bound digestive vesicles formed by the Golgi apparatus containing acid hydrolases to degrade foreign matter, endocytosed materials, and cellular debris.

Peroxisomes

Membrane-bound organelles that catabolize excess fatty acids and toxins, producing $H_2O_2$ which is subsequently converted to $H_2O$ and $O_2$ by catalase.

Central Vacuole

A large prominent plant organelle that stores water, nutrients, and pigments while exerting turgor pressure against the cell wall to maintain structural integrity.

Endosymbiosis Theory

The scientific hypothesis proposing that mitochondria and chloroplasts originated as prokaryotes that entered an endosymbiotic relationship inside ancestral eukaryotic cells.

Fluid Mosaic Model

The structural framework describing biological membranes as a semifluid bilayer of amphipathic phospholipids embedded with dynamic proteins, carbohydrates, and sterols.

Aquaporins

Specialized channel proteins within biological membranes that facilitate the rapid passive diffusion of water molecules.

Transporters (Carrier Proteins)

Membrane proteins that transfer solutes across a membrane by binding them in a hydrophilic pocket and undergoing a conformational shift.

Osmosis

The passive net movement of water molecules through a selectively permeable membrane down the water concentration gradient toward regions of higher solute concentration.

Crenation

The cellular shrinkage observed when an animal cell lacking a cell wall undergoes net water loss in a hypertonic environment.

Plasmolysis

The retraction of the plant plasma membrane away from the rigid cell wall caused by significant osmotic water loss in a hypertonic solution.

Primary Active Transport

A mechanism of membrane transport that directly hydrolyzes ATP to power ion pumps (such as the $Na^+/K^+$-ATPase) moving solutes against their chemical or electrochemical gradient.

Secondary Active Transport

Membrane transport where the movement of one solute against its concentration gradient is driven by the energy of another solute moving down its electrochemical gradient.