A Tour of the Cell - Vocabulary and Concepts

Vocabulary practice flashcards generated from lecture notes on cell biology, organelle structures, microscopy, cytoskeletal components, and intercellular connections.

Magnification

The ratio of an object's image size to its real size in microscopy.

Resolution

The measure of the clarity of an image, defined as the minimum distance of two distinguishable points.

Contrast

The visible differences in brightness between different parts of a sample.

Scanning Electron Microscope (SEM)

A microscope that focuses a beam of electrons onto the surface of a specimen, providing images that look 3-D.

Transmission Electron Microscope (TEM)

A microscope that focuses a beam of electrons through a specimen, used mainly to study the internal structure of cells.

Cell Fractionation

A technique that takes cells apart and separates the major organelles from one another using centrifuges (differential centrifugation).

Prokaryotic Cell

A cell type characterized by having no nucleus, DNA in an unbound region called the nucleoid, no membrane-bound organelles, and cytoplasm bound by the plasma membrane.

Eukaryotic Cell

A cell type characterized by having DNA in a nucleus bounded by a double membrane, membrane-bound organelles, and cytoplasm between the plasma membrane and nucleus.

Nucleoid

An unbound region in a prokaryotic cell where its DNA is located.

Plasma Membrane

A selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell.

Surface Area-to-Volume Ratio

A critical dimensional ratio where as a cell increases in size, its volume grows proportionately more than its surface area, limiting cell size.

Nuclear Envelope

A double membrane enclosing the nucleus, consisting of two lipid bilayers, that separates the nuclear contents from the cytoplasm.

Nuclear Lamina

A netlike array of protein filaments lining the nuclear side of the nuclear envelope that maintains the shape of the nucleus.

Chromatin

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

Nucleolus

A specialized structure located within the nucleus where ribosomal RNA (rRNA) synthesis occurs.

Ribosomes

Complexes made of ribosomal RNA and protein that synthesize proteins, located free in the cytosol or bound to the endoplasmic reticulum or nuclear envelope.

Endomembrane System

A collection of membranes including the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and plasma membrane, connected directly or by transfer via vesicles.

Smooth ER

The region of the endoplasmic reticulum that lacks ribosomes; functions to synthesize lipids, detoxify drugs and poisons, and store calcium ions.

Rough ER

The region of the endoplasmic reticulum studded with ribosomes; secretes glycoproteins, distributes transport vesicles, and acts as a membrane factory.

Glycoproteins

Proteins that have carbohydrates covalently bonded to them.

Golgi Apparatus

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

Lysosome

A membranous sac of hydrolytic enzymes that digests macromolecules in an acidic internal environment.

Phagocytosis

A cellular process where a cell engulfs another cell or particle, forming a food vacuole.

Autophagy

A process where lysosomes use enzymes to recycle the cell's own damaged organelles and macromolecules.

Contractile Vacuole

A membrane-bound organelle found in many freshwater protists that pumps excess water out of the cell.

Central Vacuole

A large vacuole in mature plant cells containing sap, serving as the main repository of inorganic ions (such as potassium and chloride) and playing a major role in plant growth.

Mitochondria

The sites of cellular respiration, utilizing oxygen to break down molecules and generate ATP.

Cristae

Infoldings of the inner mitochondrial membrane that present a large surface area for enzymes that synthesize ATP.

Chloroplasts

Plastid organelles found in plants and algae that contain chlorophyll and serve as the sites of photosynthesis.

Thylakoids

Membranous sacs inside chloroplasts stacked to form grana.

Stroma

The internal fluid of the chloroplast surrounding the thylakoid membrane.

Endosymbiont Theory

An evolutionary theory proposing that mitochondria and chloroplasts originated when an early ancestor of eukaryotic cells engulfed oxygen-using nonphotosynthetic and photosynthetic prokaryotes.

Peroxisomes

Specialized metabolic compartments bounded by a single membrane that contain enzymes transferring hydrogen atoms to oxygen, producing hydrogen peroxide.

Cytoskeleton

A network of fibers extending through the cytoplasm that supports cell shape, anchors organelles, and interacts with motor proteins for cell motility.

Microtubules

Hollow rods about $25\,nm$ in diameter constructed from tubulin dimers that shape the cell, guide organelle movement, and separate chromosomes during cell division.

Centrosome

A region near the nucleus in animal cells from which microtubules grow, containing a pair of centrioles each with nine triplets of microtubules arranged in a ring.

Dynein

A motor protein with two feet that walk along microtubules using ATP to drive the bending movements of cilia and flagella.

Microfilaments (Actin Filaments)

Solid rods about $7\,nm$ in diameter built as a twisted double chain of actin subunits that support cell shape and function with myosin in muscle contraction and cell motility.

Pseudopodia

Cellular extensions formed by microfilament network rearrangement that allow cells to crawl along surfaces.

Cytoplasmic Streaming

A circular flow of cytoplasm within plant cells, driven by actin-protein interactions.

Intermediate Filaments

Fibrous proteins coiled into cables with diameters from $8$ to $12\,nm$ that maintain cell shape, anchor the nucleus/organelles, and form the nuclear lamina.

Middle Lamella

A thin layer rich in pectins between primary cell walls of adjacent plant cells that glues them together.

Extracellular Matrix (ECM)

An elaborate meshwork surrounding animal cells consisting of glycoproteins (such as collagen, fibronectin, and proteoglycans) that regulates cell behavior and mechanical signaling.

Integrins

Cell-surface receptor proteins in the plasma membrane that bind ECM proteins like fibronectin and attach to microfilaments inside the cytoplasm.

Plasmodesmata

Channels perforating plant cell walls that connect adjacent cell cytoplasms, allowing water and small solutes to pass from cell to cell.

Tight Junctions

Cell junctions in epithelial tissues where neighboring plasma membranes are pressed together, creating a seal to prevent fluid leakage across cell layers.

Desmosomes

Anchoring junctions that fasten animal cells together into strong sheets, anchored by intermediate filaments.

Gap Junctions

Communicating junctions in animal cells that provide cytoplasmic channels between adjacent cells for ions and small molecules.