Comprehensive Biology: Cellular Structure, Membranes, Macromolecules, Tissues, and Microbiology

Flashcards reviewing biology lectures on cell theory, viral structure, prokaryotic genetics, membrane transport, resting and action potentials, extracellular matrix, cell junctions, and biological macromolecules.

Cell Theory

• Cells are the fundamental units of life

• All organisms are comprised of cells and cell products

• All cells originate from pre-existing cells

How do we know cells are alive?

• homeostatic

• reproducing themselves

• growing and developing

• demonstrating metabolism

• responding to stimuli

Relative Sizes of Biological Entities

A size hierarchy where a virus is approximately $20\times$ smaller than a prokaryote, which is in turn approximately $10\times$ smaller than a eukaryote.

Virus

A non-cellular, metabolically inert, subcellular, and immobile package consisting of a genome ($DNA$ or $RNA$) surrounded by a protective protein capsid.

Viral Envelope

A membrane of similar composition to cell membranes that surrounds certain viruses, bearing glycoproteins that bind to and fuse with host membranes to deceive the cell and gain entry.

Prokaryotic Cell

A small, simple, unicellular organism lacking most membrane-bound organelles (such as mitochondria and cytoskeleton) and containing a nucleoid, circular chromosome, ribosomes, and typically a peptidoglycan cell wall.

What are the 3 types of recombination in genetic variation?

• transformation

• Conjugation

• Transduction

Transformation

A mechanism of horizontal genetic recombination where a prokaryotic cell picks up naked foreign genes directly from the surrounding environment.

Conjugation

A form of genetic recombination in prokaryotes involving the direct transfer of genes from one bacterial cell to another.

Transduction

The viral transfer of bacterial genes between cells mediated by viruses (bacteriophages).

F-Plasmid

A small, self-replicating extrachromosomal $DNA$ molecule carrying the fertility factor ($F$ factor) that allows a donor ($F^+$) cell to initiate conjugation and convert an $F^-$ recipient cell into an $F^+$ cell.

R-Plasmid

A plasmid carrying antibiotic resistance genes encoding proteins that neutralize antibiotics; can carry more than $10$ resistance genes simultaneously alongside transfer factors.

Virulence Factors

Inheritable bacterial traits that assist in disease production by helping bacteria adhere to surfaces, invade host tissues, evade immune defenses, and damage host structures.

Exotoxins

Soluble toxic protein secretions produced by bacteria that can elicit pathological symptoms in a host even in the absence of the bacterial cells themselves (e.g., botulism and cholera toxins).

Endotoxins

Lipid/toxin components residing in the outer membrane of Gram-negative bacteria (such as Salmonella) that trigger host disease responses.

Endomembrane System

An interconnected internal membrane network in eukaryotic cells comprising the nuclear envelope, endoplasmic reticulum ($ER$), Golgi apparatus, lysosomes, and the plasma membrane.

Rough Endoplasmic Reticulum (Rough ER)

Membranous tubules (cisternae) studded with ribosomes that synthesize secretory proteins for export into cisternal spaces and vesicles, as well as manufacture new cellular membrane.

Smooth Endoplasmic Reticulum (Smooth ER)

Regions of the endoplasmic reticulum with few to no ribosomes that catalyze lipid synthesis (e.g., vertebrate sex hormones), carbohydrate metabolism (e.g., glycogen conversion to glucose in liver cells), detoxification, and calcium pumping for muscle contraction.

Golgi Apparatus

An organelle composed of flattened membranous stacks (Golgi bodies) that receives transport vesicles from the $ER$ at its cis face, tags, sorts, and concentrates products, and pinches off targeted vesicles at its trans face.

Mitochondria

Semi-autonomous, double-membraned cellular powerhouses responsible for cellular respiration ($\text{sugar/fats} + O_2 \rightarrow CO_2 + H_2O + \text{energy (ATP)}$), possessing an infolded inner membrane (cristae) and a matrix containing proteins, $DNA$, and ribosomes.

Phospholipid

An amphipathic molecule composed of a polar glycerol and phosphate 'head' attached to two non-polar fatty acid chain 'tails'.

Fluid Mosaic Model

A model of membrane structure describing a fluid lipid bilayer interspersed with integral transmembrane proteins, peripheral proteins attached to supporting fibers, and exterior glycoproteins and glycolipids.

Electrochemical Gradient

The dual driving force acting on ion movement across a membrane, determined jointly by the chemical concentration gradient and the electrical potential difference across the bilayer.

Facilitated Diffusion

Passive, protein-mediated transport that accelerates the movement of specific solutes down a favorable electrochemical gradient without consuming metabolic energy.

Osmosis

The net movement of water across a selectively permeable membrane from a region of higher water free energy (lower solute concentration) to lower free energy (higher solute concentration).

Hypertonic Solution

A comparative solution containing a higher solute concentration (lower water concentration) relative to another solution separated by a membrane.

Hypotonic Solution

A comparative solution containing a lower solute concentration (higher water concentration) relative to another solution separated by a membrane.

Primary Active Transport

The physiological pumping of solutes across a membrane against their electrochemical gradient directly powered by cellular energy input (such as $ATP$ hydrolysis).

Sodium-Potassium ($Na^+/K^+$) Pump

An electrogenic primary active transport carrier protein that expels $3\,Na^+$ ions and imports $2\,K^+$ ions per cycle, yielding a net loss of one positive charge and polarizing the membrane.

Resting Membrane Potential

The steady electrical voltage across an unstimulated cell membrane (approximately $-70\,mV$ in neurons), sustained by $Na^+/K^+$ pumps, impermeable intracellular anions, and high $K^+$ leak permeability.

Cotransport (Secondary Active Transport)

A mechanism where the passive downhill flow of an ion ($Na^+$ or $H^+$) provides the energy to drive the simultaneous uphill accumulation of another solute (such as amino acids or glucose) against its concentration gradient.

Symport

A transport protein that carries two distinct chemical species across the membrane simultaneously in the same physical direction.

Antiport

A counter-transport carrier protein that moves two different solutes across the membrane in opposite directions (e.g., $Na^+$ moving in while another solute moves out).

Hyperkalemic Periodic Paralysis (HYPP)

An inherited defect in American Quarter Horses resulting from abnormal voltage-gated $Na^+$ channels, where elevated blood $K^+$ provokes slight depolarisation, runaway $Na^+$ influx, and failure to respond to nervous stimulation.

Cystic Fibrosis

A disease caused by absent or defective $Cl^-$ channels that results in abnormally thick and sticky mucus secretions in the respiratory and digestive systems.

Phagocytosis

A form of endocytosis ('cell eating') involving the uptake of large particulate matter into intracellular vesicles.

Pinocytosis

A type of endocytosis ('cell drinking') by which fluid droplets containing solutes are nonspecifically brought into the cell.

Transcytosis

A cellular transport route combining endocytosis at one plasma membrane surface followed by intracellular transport and exocytosis at the opposite surface.

Action Potential

An 'all-or-nothing' electrical nerve impulse generated via voltage-gated channels ($Na^+$ and $K^+$) that self-propagates along an axon without losing amplitude despite membrane resistance.

Depolarisation

The initial phase of an action potential wherein stimulus-gated or voltage-gated $Na^+$ channels open, allowing rapid inward influx of $Na^+$ down its electrochemical gradient.

Undershoot (Hyperpolarisation)

The terminal phase of an action potential where voltage-gated $K^+$ outflow channels remain open while $Na^+$ channels close, temporarily driving the membrane potential below its resting state.

Synapse

The functional contact junction where an axon terminal communicates chemically or electrically with an adjacent cell (another neuron or an effector cell).

Tight (Occluding) Junctions

Intercellular connections in epithelial sheets where adjacent cell membranes are fused by protein bands, forming an impermeable barrier to leakage of extracellular fluids.

Anchoring Junctions

Mechanical protein junctions (e.g., desmosomes, hemidesmosomes, and adherens junctions) that link cytoskeletons of neighbouring cells or bind cells to the ECM in tissues subjected to mechanical stress.

Communicating (Gap) Junctions

Junctions composed of transmembrane protein complexes (connexons) that align to form regulated cytoplasmic channels for direct ion and small molecule exchange between cells.

Extracellular Matrix (ECM)

A loose lattice matrix of protein fibres (such as collagen) and adhesive glycoproteins (such as fibronectin) embedded in highly hydrated, negatively charged polysaccharides that provides structure, support, and cellular regulation.

Basal Lamina

A specialised layer of extracellular matrix that directly underlies and anchors epithelial tissues.

Collagen Fibres

Abundant fibrous connective tissue proteins constructed from three polypeptides wound into a triple helix, which assemble sequentially into collagen fibrils and robust collagen fibres.

Functional Groups

Specific chemical configurations attached to carbon skeletons that retain distinct chemical properties, such as the carboxyl group ($-COOH$) which dissociates into $-COO^- + H^+$ to confer acidic properties.

Condensation (Dehydration) Reaction

An enzymatic, energy-consuming synthesis reaction that joins monomeric subunits into macromolecules with the simultaneous removal and release of a water molecule.

Hydrolysis Reaction

An enzymatic, energy-releasing cleavage reaction that breaks covalent bonds in polymers by adding a molecule of water.

Amino Acid

The monomeric building block of proteins, consisting of a central carbon atom bonded to an amino group ($-NH_2$), a carboxyl group ($-COOH$), a hydrogen atom, and a variable chemical side chain (R-group).

Primary Structure of Proteins

The unique, linear sequence of amino acids joined together by covalent peptide bonds in a polypeptide chain.

Tertiary Structure of Proteins

The final folded 3D conformation of a protein, driven by tucking non-polar R-groups into the hydrophobic interior and exposing polar groups to the exterior, stabilized by hydrogen bonds, ionic bonds, van der Waals forces, and covalent disulphide bonds.

Denaturation

The loss of a protein's folded native three-dimensional conformation and biological function triggered by adverse changes in temperature, pH, ionic concentration, or exposure to organic solvents.

Glycosidic Linkage

A covalent bond formed between two monosaccharides through a dehydration reaction to create a disaccharide or polysaccharide.

Glycogen

A compact, finely branched glucose storage polysaccharide in animal liver and muscle cells that is hydrolysed into glucose units when cellular demand for energy increases.

Lipids

The only class of major biological macromolecules that does not consist of repeating polymers; characterised by highly diverse structures, insolubility in water (little or no affinity for water), and assembly via dehydration into ester linkages.

Waxes

Lipids formed by joining a long-chain fatty acid to a long-chain fatty alcohol, providing protective waterproof coatings on biological surfaces (e.g., sebum and cerumen).