PB001 Prokaryotic and Eukaryotic Cells

Comprehensive vocabulary flashcards covering cell theory, microscopy types, prokaryotic versus eukaryotic structures, bacterial wall composition, horizontal gene transfer, growth kinetics, endomembrane systems, and organelle functions based on PB001 lecture notes.

Cell Theory

The foundational biological theory comprising three tenets: (1) Cells are the fundamental units of life, (2) All living things are made of cells, and (3) All cells arise only by division from pre-existing cells.

Robert Hooke

The English scientist who in 1665 first described and coined the term 'cells' after observing the microscopic structure of cork.

Antonie van Leeuwenhoek

The Dutch microscopist who in the 1670s first observed and described living cells in pond water (termed 'animalcules') and the first bacterial forms.

HeLa Cells

The first immortalised human cell line and the first cells to grow in culture, isolated without consent in 1951 from a cervical cancer biopsy taken from Henrietta Lacks (1920-1951).

Resolution

The minimum distance by which two distinct points or objects can be separated and still be distinguished as separate entities under a microscope.

Light Microscope

An optical instrument using visible light that achieves a maximum magnification of $1000\times$ and a resolution limit of approximately $200\,\text{nm}$.

Fluorescence Microscope

An optical microscope that uses fluorescence to generate images, achieving a maximum magnification of $2000\times$ and a resolution limit of approximately $200\,\text{nm}$.

Electron Microscope

An instrument using an accelerated electron beam as a radiation source, achieving a maximum magnification of $10{,}000{,}000\times$ and a resolution of $0.5\,\text{nm}$.

Scanning Electron Microscopy (SEM)

An electron microscopy technique that scans the surface of a specimen with a focused electron beam to produce a three-dimensional image of external surface topography via electron deflection.

Transmission Electron Microscopy (TEM)

An electron microscopy technique that passes an electron beam through ultrathin tissue sections to yield high-resolution images of internal cellular ultrastructure.

Prokaryote

A single-celled organism (such as bacteria and archaea) characterised by a small, simple cellular structure lacking a membrane-bound nucleus and membrane-bound organelles.

Eukaryote

An organism (including animals, plants, fungi, and protists) whose cells contain a distinct membrane-bound nucleus and specialized membrane-enclosed organelles.

Peptidoglycan (Murein)

A mesh-like polymer forming the bacterial cell wall consisting of alternating sugar units of $N\text{-acetylglucosamine (NAG)}$ and $N\text{-acetylmuramic acid (NAM)}$ cross-linked by short peptide chains.

Gram-Positive Bacteria

Bacteria featuring a thick, multilayered peptidoglycan layer ($20\text{ to }80\,\text{nm}$ thick) containing teichoic and lipoteichoic acids, lacking an outer membrane, and possessing a narrow or absent periplasmic space (e.g., Staphylococcus, Streptococcus, Bacillus, Clostridium).

Gram-Negative Bacteria

Bacteria possessing a thin peptidoglycan layer ($1.5\text{ to }10\,\text{nm}$ thick), a wide periplasmic space, and an outer lipid bilayer membrane containing lipopolysaccharides (LPS), lipoproteins, and porins, but lacking teichoic acids (e.g., Escherichia coli, Salmonella, Pseudomonas, Vibrio).

Gram Staining

A four-step differential staining procedure: (1) Crystal violet (primary stain, $1\,\text{min}$), (2) Iodine (mordant, $1\,\text{min}$), (3) Alcohol (decoloriser that removes dye from Gram-negative walls, $10\,\text{sec}$), and (4) Safranin (counterstain adhering to Gram-negative walls, $1\,\text{min}$).

Binary Fission

The primary asexual reproductive process in bacteria involving copying of the single circular chromosome, cell elongation, formation of an inward partitioning wall (septum), and cellular cleavage into two identical daughter cells.

Bacterial Conjugation

A horizontal gene transfer mechanism where plasmid DNA (such as the $\text{F-plasmid}$) is directly transferred from a donor ($\text{F}^+$ cell) to a recipient ($\text{F}^-$ cell) via a specialised sex pilus.

Bacterial Transformation

A horizontal gene transfer process in which a competent recipient bacterium takes up naked, free environmental DNA fragments released from a dead bacterial cell and integrates them into its genome.

Bacterial Transduction

The bacteriophage-mediated transfer of bacterial DNA fragments from an infected donor bacterium into a new recipient bacterium during viral replication and infection.

Endospore Sporulation

An adaptive survival mechanism triggered by carbon or nitrogen starvation, in which a vegetative bacterium produces a metabolically dormant, highly resistant endospore capable of surviving extreme heat, radiation, desiccation, and toxic chemicals.

Bacterial Growth Phases

The four population growth stages in a closed culture: Lag phase (adaptation, high metabolism, no division), Log/exponential phase (rapid, constant cell division), Stationary phase (nutrient depletion and toxic waste equalising division and death rates), and Death phase (population decline due to toxic accumulation).

Appendage-Dependent Motility

Bacterial movement mediated by surface structures, comprising Swarming (multicellular coordinated migration across surfaces powered by hyperflagellation), Swimming (individual liquid movement driven by rotating flagella), and Twitching (jerky surface movements mediated by Type IV pili extension and retraction).

Appendage-Independent Motility

Bacterial movement that does not utilize flagella or pili, comprising Gliding (smooth active surface translocation driven by focal adhesion complexes and motor proteins) and Sliding (passive expansion propelled by colony growth pressure and cell division).

Bacterial Flagellar Motor

A complex transmembrane rotary nanomachine composed of approximately $30$ distinct protein components spanning the inner and outer membranes to generate torque for swimming motility.

Phospholipid Bilayer

An amphipathic semi-permeable lipid membrane where hydrophilic phosphate-containing heads face the external aqueous environments and hydrophobic fatty acid tails pack together facing inward; proteins contribute roughly $50\%$ of total plasma membrane mass in animal cells.

Membrane Permeability

The property of the lipid bilayer permitting passive diffusion of small uncharged molecules ($\text{O}_2, \text{CO}_2, \text{H}_2\text{O}, \text{NH}_3$) and lipid-soluble steroids/hydrocarbons, while being impermeable to large polar molecules ($\text{glucose}$) and ions ($\text{Na}^+, \text{K}^+, \text{H}^+, \text{Cl}^-, \text{Ca}^{2+}$).

Nucleolus

A dense, non-membrane-bound subnuclear compartment composed of RNA, DNA, and proteins where ribosomal RNA (rRNA) is transcribed and assembled into ribosomes; prominent in high-protein-producing cells such as hepatocytes.

Nuclear Envelope

A double-membrane lipid bilayer perforating with nuclear pores that encloses genetic material, separating the nucleoplasm from the cytoplasm; its outer membrane is continuous with the rough endoplasmic reticulum.

Nucleosome

The fundamental structural repeating unit of chromatin consisting of a section of double-stranded DNA wound around an octamer core of histone proteins in a 'beads on a string' organization.

Rough Endoplasmic Reticulum (RER)

An interconnected network of flattened membrane sheets studded with ribosomes on its cytosolic surface; specialised for protein synthesis, folding, glycosylation, quality control, and membrane generation.

Smooth Endoplasmic Reticulum (SER)

A ribosome-free tubular membrane network responsible for lipid and steroid hormone synthesis, detoxification of drugs and alcohol, glucose release from glycogen, and intracellular $\text{Ca}^{2+}$ storage and release.

Golgi Apparatus

A stacked membrane-bound organelle discovered by Camillo Golgi (1843-1926) that receives, chemically modifies (e.g., carbohydrate labelling), sorts, and packages ER-derived proteins and lipids for dispatch via vesicles.

Lysosome

A membrane-enclosed catabolic organelle containing acid hydrolases active at $\text{pH } 5$; responsible for intracellular digestion through endocytosis, autophagy of worn-out organelles, and phagocytosis (macrophages possess up to $1000$ lysosomes).

Peroxisome

A self-replicating, membrane-enclosed eukaryotic vesicle containing oxidative enzymes that oxidize organic compounds and break down toxic hydrogen peroxide ($\text{H}_2\text{O}_2$); also involved in lipid biosynthesis and photorespiration.

Mitochondrion

A double-membrane organelle containing its own circular DNA (mtDNA) and ribosomes; generates cellular ATP via the citric acid cycle and oxidative phosphorylation, regulates calcium homeostasis, mediates beta-oxidation, and triggers apoptosis through cytochrome C release.

Cristae

The deep finger-like inward folds of the mitochondrial inner membrane that substantially amplify the surface area available to house the electron transport chain complexes and ATP synthase.

Cytoskeleton Filaments

The dynamic protein network maintaining eukaryotic cell shape, organelle anchorage, and intracellular transport, composed of Microfilaments ($8\,\text{nm}$, actin), Intermediate filaments ($10\,\text{nm}$, keratin, vimentin, laminin, desmin), and Microtubules ($25\,\text{nm}$, tubulin).

Axoneme (9+2 Structure)

The core microtubular arrangement found in eukaryotic cilia and flagella consisting of nine outer doublet microtubules encircling two central singlet microtubules, enclosed by the plasma membrane and anchored to a basal body.

Centriole

A cylindrical organelle composed of nine sets of microtubule triplets ($9 \times 3$ array) situated within the centrosome that organizes microtubule growth and assembly of the mitotic spindle during cell division.

Central Vacuole

A prominent, membrane-enclosed fluid storage compartment in plant cells that maintains hydrostatic turgor pressure and stores water, nutrients, and waste products.

Chloroplast

A double-membrane photosynthetic plastid in plants containing circular DNA, ribosomes, a fluid stroma for the Calvin cycle, and stacks of chlorophyll-containing thylakoid membranes (grana) for capturing light energy.