Eukaryotic and Prokaryotic Cell Biology, Cytoskeleton, and Microscopy

Comprehensive vocabulary flashcards covering eukaryotic and prokaryotic cell structures, organelle functions, protein trafficking, cytoskeletal elements, microscopy, and endosymbiosis.

Organelle

A cellular structure that performs a specific function inside a cell; organelles can be membrane-bound or non-membrane-bound, while structures such as the cytoplasm, cell wall, and cell surface membrane are not considered organelles.

Animal Cell Ultrastructure

The internal architecture of an animal cell containing membrane-bound organelles (such as the nucleus, mitochondria, rough and smooth endoplasmic reticulum, Golgi body, and lysosomes) and non-membrane-bound structures (such as ribosomes and a centrosome with two centrioles at right angles).

Plasmodesma

A microscopic channel traversing the cell wall of plant cells that enables transport and communication between individual plant cells.

Tonoplast

The partially permeable membrane that encloses the large permanent vacuole in plant cells, separating the cell sap from the cytoplasm.

Peptidoglycan

A cross-linked polymer that forms the cell wall of prokaryotic cells.

Pili

Hair-like surface appendages found on prokaryotic cells that allow them to attach to other cells and transfer plasmid or chromosomal DNA.

Capsule

An outer layer made of polysaccharide in prokaryotic cells that provides additional protection against attacks by white blood cells.

Bacterial Flagellum

A helical prokaryotic motility structure composed of the protein flagellin that rotates in a propeller-like manner to drive cellular propulsion.

Eukaryotic Flagellum

A motility organelle constructed from tubulin microtubules arranged in a $9+2$ pattern (nine pairs surrounding a central pair) that generates propulsion using a whipping motion.

Ribosome

A non-membrane-bound complex of rRNA and proteins that serves as the site of translation during protein synthesis, measuring $70\text{S}$ in prokaryotes, chloroplasts, and mitochondria, and $80\text{S}$ in eukaryotic cytoplasm.

Protein Secretion Pathway

The intracellular route where a gene is transcribed into mRNA in the nucleus, exits through nuclear pores, is translated at the rough ER ribosomes, packaged into transport vesicles to the Golgi apparatus cis face for modification, and exported from the trans face via secretory vesicles for exocytosis.

Exocytosis

The process where a secretory vesicle fuses with the cell surface membrane to release its protein contents outside the cell.

Cytoskeleton

A cellular network of protein fibres that provides mechanical stability, maintains cell shape, holds organelles in place, and controls the internal and external movement of the cell.

Microfilaments

Contractile protein fibres with a diameter of $7\,\text{nm}$ composed of polymerised actin that thicken the cell cortex to resist tension, form the contractile ring during cell division, work with myosin, and rapidly assemble and disassemble to allow cell movement.

Microtubules

Small hollow protein tubes with a diameter of $25\,\text{nm}$ composed of polymerised dimers of $\alpha\text{-tubulin}$ and $\beta\text{-tubulin}$ that act as tracks for organelle movement, pull chromosomes during division, and form cilia, flagella, and centrioles.

Intermediate Filaments

Stable cytoskeletal fibres with a diameter of $8-10\,\text{nm}$ made from strands of fibrous proteins (such as keratin) wound together, functioning to provide mechanical strength and anchor organelles throughout the cell.

Endosymbiotic Theory

The theory that chloroplasts and mitochondria originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells billions of years ago, supported by their circular DNA, $70\text{S}$ ribosomes, and prokaryotic-like biochemistry.

Magnification

The number of times a specimen has been enlarged to yield a larger image.

Resolution

The shortest distance between points on an object that can still be distinguished as two separate entities.

Axoneme

The central microtubule core of cilia and flagella, exhibiting a $9+2$ arrangement in motile cilia and a $9+0$ arrangement in primary cilia.

Plasma Membrane

A partially permeable phospholipid bilayer (approximately $7\,\text{nm}$ wide) with hydrophilic heads facing outward and hydrophobic tails inward that controls the exchange of materials between internal and external environments.

Nuclear Envelope and Nuclear Pores

A double membrane enclosing the nucleus containing small perforations that regulate cellular communication by allowing hormones and enzymes to enter and mRNA to exit.

Nucleolus

A dense non-membrane-bound structure inside the nucleus where ribosomal RNA (rRNA) is produced.

Cristae

Highly folded extensions of the inner mitochondrial membrane that provide a large surface area for cellular respiration and ATP synthesis.

Mitochondrial Matrix

The fluid-filled interior space of a mitochondrion containing respiration enzymes, circular mitochondrial DNA, and $70\text{S}$ ribosomes.

Rough Endoplasmic Reticulum (RER)

A series of flattened membrane-bound sacs (cisternae) continuous with the nuclear envelope and coated with ribosomes, responsible for the synthesis, modification into tertiary structure, and packaging of proteins.

Smooth Endoplasmic Reticulum (SER)

A series of flattened membrane sacs lacking surface ribosomes that synthesizes, stores, and transports lipids, carbohydrates, and steroid hormones such as oestrogen and testosterone.

Golgi Apparatus

An organelle consisting of flattened membrane cisternae that receives transport vesicles at its cis face, modifies proteins, and repackages them into secretory vesicles that exit at its trans face.

Centrioles

Paired organelles composed of parallel microtubules surrounding a central cavity that form the centrosome to organize spindle fibres during cell division, and are also found in isolation at the basal regions of cilia and flagella.

Lysosome

A specialized membrane-bound vesicle containing hydrolytic enzymes designed to break down biological waste material, cellular debris, and engulfed pathogens.

Microvilli

Projections of the cell surface membrane that increase surface area for absorption in specialized epithelial cells.

Thylakoids and Grana

Interconnected, fluid-filled, flattened membrane discs inside a chloroplast that form stacks termed grana (singular: granum), linked by lamellae to carry out photosynthesis.

Stroma

The fluid enclosed by the inner membrane of the chloroplast surrounding the grana, containing chloroplast circular DNA, $70\text{S}$ ribosomes, and photosynthetic enzymes.

Starch Grain

An intracellular plant structure that stores glucose in the form of insoluble starch within the cytoplasm or chloroplasts.