Structure and Functions of a Eukaryotic Cell

Comprehensive vocabulary flashcards covering eukaryotic organelles, the endomembrane system, cytoskeleton, flagellar and ciliary locomotion, and plasma membrane dynamics for SBI4U biology.

Nucleus

The eukaryotic organelle that houses genetic information (chromatin), bounded by a double membrane known as the nuclear envelope.

Nuclear Envelope

A double membrane consisting of an inner and outer lipid bilayer that encloses the nucleus, separating genetic material from the cytoplasm, and is continuous with the endoplasmic reticulum.

Pore Complexes (Nuclear Pores)

Protein-lined openings perforating the nuclear envelope that regulate the transport of proteins, RNAs, and macromolecules between the nucleus and the cytoplasm.

Nuclear Lamina

A net-like array of protein filaments lining the inner surface of the nuclear envelope that mechanically supports the nuclear structure and shape.

Nucleolus

A prominent region within the non-dividing nucleus responsible for synthesizing ribosomal RNA (rRNA) and assembling ribosome subunits.

Chromatin

The complex of DNA and associated proteins that constitutes eukaryotic chromosomes within the nucleus.

Ribosomes

Cellular particles composed of ribosomal RNA (rRNA) and protein that carry out protein synthesis in the cytosol or attached to membranes.

Free Ribosomes

Ribosomes suspended in the cytosol that synthesize soluble proteins functioning within the cytosol.

Bound Ribosomes

Ribosomes attached to the outside of the endoplasmic reticulum or nuclear envelope that synthesize membrane-bound, organelle-targeted, or secretory proteins.

Large Ribosomal Subunit

The larger structural subunit of a ribosome that coordinates with the small subunit during translation.

Small Ribosomal Subunit

The smaller structural subunit of a ribosome that joins with the large subunit to translate messenger RNA into polypeptide chains.

Endomembrane System

A coordinated network of internal cellular membranes that regulates protein traffic and performs metabolic functions, consisting of the nuclear envelope, ER, Golgi apparatus, lysosomes, vacuoles, and plasma membrane.

Endoplasmic Reticulum (ER)

An extensive labyrinth of membranous tubules and sacs continuous with the nuclear envelope, divided into smooth and rough functional regions.

Smooth ER

The region of the endoplasmic reticulum that lacks ribosomes on its surface, specialized for lipid synthesis, carbohydrate metabolism, and detoxification.

Rough ER

The region of the endoplasmic reticulum studded with ribosomes on its outer surface, active in protein synthesis and membrane production.

Transport Vesicles

Membranous spheres that pinch off from the ER and Golgi apparatus to transport proteins and other materials throughout the cell.

Golgi Apparatus

An organelle consisting of flattened membranous sacs (cisternae) that modifies products of the ER, manufactures certain macromolecules, and sorts and packages materials into transport vesicles.

Cisternae

The flattened, membrane-bound sacs that comprise the structural stacks of the Golgi apparatus.

cis Face (Golgi Apparatus)

The receiving side of the Golgi apparatus, situated near the ER, where transport vesicles fuse to deliver cargo.

trans Face (Golgi Apparatus)

The shipping side of the Golgi apparatus where vesicles pinch off and depart to other sites, including the plasma membrane.

Lysosome

A membranous sac of hydrolytic enzymes that digests macromolecules, including proteins, fats, polysaccharides, and nucleic acids.

Hydrolytic Enzymes

Digestive enzymes packaged within lysosomes that catalyze the breakdown of macromolecules by hydrolysis.

Phagocytosis

A cellular digestion process where a cell engulfs food particles into a food vacuole, which then fuses with a lysosome to degrade the molecules.

Autophagy

The cellular process in which lysosomes use hydrolytic enzymes to recycle the cell's own damaged organelles and macromolecules.

Central Vacuole

A large membrane-bound organelle found in plant cells that stores water, nutrients, and waste, providing turgor pressure to maintain cell shape.

Tonoplast

The selective membrane enclosing the central vacuole in eukaryotic plant cells.

Mitochondria

Organelles with a smooth outer membrane and an inner membrane folded into cristae that serve as the primary site of cellular respiration and ATP synthesis.

Cristae

Infoldings of the inner mitochondrial membrane that provide a large surface area for ATP-synthesizing enzymes.

Intermembrane Space (Mitochondria)

The narrow fluid-filled compartment situated between the outer membrane and the inner membrane of a mitochondrion.

Mitochondrial Matrix

The inner compartment enclosed by the mitochondrial inner membrane containing free ribosomes, DNA, and enzymes that catalyze metabolic steps of cellular respiration.

Chloroplasts

Photosynthetic organelles found in plant cells and algae that contain chlorophyll and capture light energy to produce glucose.

Chlorophyll

The green photosynthetic pigment housed inside chloroplasts that captures light energy.

Thylakoid

A flattened, disc-shaped membranous sac inside a chloroplast where light reactions of photosynthesis occur.

Granum

A stack of interconnected thylakoid discs inside a chloroplast.

Stroma

The dense fluid-filled matrix surrounding the thylakoid membrane system inside a chloroplast.

Cell Wall

A rigid extracellular structure surrounding cells of plants, fungi, and protists that provides support and protection; composed mostly of polysaccharides and/or glycoproteins.

Plasmodesmata

Microscopic membrane-lined channels traversing plant cell walls that allow direct transport and communication between adjacent plant cells.

Cytoskeleton

An internal cellular network of protein filaments that provides structural support, anchors the plasma membrane and organelles, transports vesicles, and facilitates cell motility.

Microfilaments

Thin cytoskeletal filaments approximately $7\,\text{nm}$ in diameter composed of actin monomers, functioning in structural support and cell movement.

Intermediate Filaments

Fibrous cytoskeletal elements measuring $8\text{--}12\,\text{nm}$ in diameter that provide tensile strength and anchor the nucleus and other organelles in place.

Microtubules

Hollow cytoskeletal cylinders approximately $25\,\text{nm}$ in diameter made of tubulin dimers ($\alpha$-tubulin and $\beta$-tubulin monomers) that guide organelle transport and maintain cell shape.

Pseudopodia

Temporary cytoplasmic extensions driven by cytoskeletal rearrangement used by amoeboid cells for locomotion and engulfment.

Cilia

Hair-like cellular appendages that beat back and forth to enable organism movement or sweep debris across surfaces, such as in the respiratory tract.

Power Stroke (Cilia)

The active, force-generating phase of ciliary movement that pushes against the surrounding medium to generate propulsion or fluid movement.

Recovery Stroke (Cilia)

The return phase of ciliary movement where the cilium bends close to the cell surface to reset its position with minimal resistive drag.

Flagella

Long, whip-like appendages (typically one or two per cell) that generate undulating wave-like motion to propel a cell through a liquid medium.

Bacterial Flagellum

A specialized locomotive appendage of a bacterium that extends outward through the capsule, cell wall, and plasma membrane to drive motility.

Nucleoid

The non-membrane-enclosed region in a bacterial cell that contains its circular DNA.

Plasma Membrane

A semi-permeable bilayer of phospholipids that encloses the cell, separating the internal cytoplasm from the extracellular fluid.

Semi-Permeability

The property of the plasma membrane that selectively controls which molecules and ions can enter and exit the cell.

Fluid Mosaic Model

The membrane model proposed by Jonathan Singer and Garth Nicolson describing the cell membrane as a bilayer of phospholipids embedded with cholesterol, proteins, and glycoproteins in dynamic motion.

Phospholipid Bilayer

A two-layered sheet formed by amphipathic phospholipids with hydrophilic phosphate heads oriented toward aqueous environments and hydrophobic fatty acid tails facing inward.

Lateral Movement (Phospholipids)

The rapid side-to-side shifting of phospholipids within the same membrane monolayer, occurring at a rate of approximately $10^7$ times per second.

Flip-Flop Movement (Phospholipids)

The rare migration of a phospholipid molecule across from one leaflet of the bilayer to the opposite leaflet, occurring approximately once per month.

Integral Proteins

Membrane proteins embedded within the hydrophobic lipid core, spanning across the membrane and exposed on both the extracellular and intracellular surfaces.

Peripheral Proteins

Membrane proteins located on the exterior or interior surfaces of the phospholipid bilayer that are not embedded within the hydrophobic core.

Carrier Protein

An integral transport protein that selectively binds solutes (such as $\text{Na}^+$ and $\text{K}^+$) and changes conformation to transport them across the membrane.

Channel Protein

A transmembrane protein containing a hydrophilic pore that allows specific ions or small polar molecules to diffuse passively across the membrane.

Glycoproteins

Membrane proteins bonded to carbohydrate chains (oligosaccharides) exposed on the cell surface that function in cell-to-cell recognition.

Membrane Cholesterol

A steroid lipid embedded in animal cell membranes that buffers membrane fluidity by restraining movement at high temperatures and preventing tight packing of phospholipids at low temperatures.