MCDB6: A Tour of the Cell and Cellular Transport

Vocabulary practice flashcards covering cell structure, organelles, membranes, and cellular transport mechanisms based on the MCDB6 Week 4-5 study guide.

Light microscope (LM)

A microscope where visible light is passed through a specimen and through glass lenses, which refract the light to magnify the image up to approximately $1000\times$ the size of the actual specimen.

Magnification

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

Resolution

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

Contrast

The difference in brightness between the light and dark areas of an image, which can be enhanced by staining or labeling cell components.

Scanning electron microscopes (SEMs)

Microscopes that focus a beam of electrons onto the surface of a specimen to produce images that appear three-dimensional.

Transmission electron microscopes (TEMs)

Microscopes that focus a beam of electrons through a specimen to study the internal structure of cells.

Cell fractionation

A technique that breaks up cells (such as by sonication) and separates their components based on size using centrifugation.

Nucleoid

The unbound physical region in a prokaryotic cell where the single circular duplex of DNA is located.

Plasma membrane (PM)

A selective barrier consisting of a double layer of phospholipids with embedded proteins that allows the passage of oxygen, nutrients, and waste.

Nuclear envelope

A double membrane enclosing the nucleus, each layer consisting of a lipid bilayer, which separates the nucleus from the cytoplasm and contains nuclear pores that regulate entry and exit.

Chromatin

The complex of DNA and protein that makes up eukaryotic chromosomes and condenses into discrete chromosomes as a cell prepares to divide.

Nucleolus

A structure located inside the nucleus that serves as the site of ribosomal RNA ($\text{rRNA}$) synthesis.

Ribosomes

Protein factories composed of complexes of $\text{rRNA}$ that carry out protein synthesis either freely in the cytosol or bound to the endoplasmic reticulum or nuclear envelope.

Endomembrane system

A cellular system that regulates protein traffic and performs metabolic functions, consisting of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and the plasma membrane.

Smooth ER

A region of the endoplasmic reticulum lacking ribosomes that synthesizes lipids, metabolizes carbohydrates, detoxifies drugs and poisons, and stores calcium ions.

Rough ER

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

Golgi apparatus

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

Lysosomes

Membranous sacs containing hydrolytic enzymes that work best in an acidic environment to digest macromolecules.

Phagocytosis

A process where a cell engulfs another cell or food particle, forming a food vacuole that fuses with a lysosome to digest the contents.

Autophagy

A recycling mechanism used by lysosomes to digest and recycle the cell's own dead or damaged organelles and macromolecules.

Tay-Sachs Disease

An inherited lysosomal storage disease caused by a defect in an enzyme needed to degrade membrane glycolipids, causing abnormal accumulation in brain cells, leading to blindness, dementia, and death by $3\text{--}4$ years of age.

Contractile vacuoles

Vacuoles found in freshwater protists (such as Paramecium caudatum) that pump excess water out of the cell to maintain water balance.

Central vacuoles

Large vesicles found in mature plant cells that hold organic compounds and water.

Cristae

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

Mitochondrial matrix

The compartment enclosed by the inner membrane of the mitochondrion where some of the metabolic steps of cellular respiration are catalyzed.

Chloroplasts

Photosynthetic organelles found in plants and algae that capture light energy and contain the green pigment chlorophyll and enzymes for photosynthesis.

Peroxisomes

Specialized single-membrane metabolic compartments that carry out oxidative reactions, producing hydrogen peroxide and converting it to water.

Endosymbiont theory

The theory that an early ancestor of eukaryotic cells engulfed an oxygen-using, non-photosynthetic prokaryote, forming an endosymbiotic relationship that evolved into mitochondria, with some cells later engulfing photosynthetic prokaryotes to yield chloroplasts.

Cytoskeleton

A dynamic network of fibers extending throughout the cytoplasm that organizes structures and activities, anchors organelles, and produces motility via motor proteins.

Microtubules

Hollow rods constructed from globular protein dimers called tubulin that function in maintaining cell shape, support, cellular motility, and separation of chromosomes during cell division.

Microfilaments (actin filaments)

Thin, solid rods built from globular actin subunits that bear tension to resist pulling forces and interact with myosin to produce cellular motility.

Intermediate filaments

Permanent cytoskeletal fibers found only in some animals (vertebrates) that reinforce cell shape and fix organelles into place.

Centrosome

A region near the nucleus in animal cells that acts as a microtubule-organizing center, containing a pair of centrioles each made of nine triplets of microtubules arranged in a ring.

Dynein

A motor protein with arms that alternately contact, move, and release outer microtubules to generate the bending movement of cilia and flagella.

Nexin

A flexible cross-linking protein that holds outer doublets together in cilia and flagella so that the movement of dynein produces bending.

Extracellular matrix (ECM)

An external meshwork covering animal cells composed of glycoproteins such as collagen, proteoglycans, and fibronectin.

Integrins

Cell-surface receptor proteins embedded in the plasma membrane that bind to extracellular matrix (ECM) proteins.

Plasmodesmata

Channels perforating plant cell walls that allow water, small solutes, and some proteins and RNA to pass from cell to cell.

Tight junctions

Cell junctions that form a watertight seal between animal cells to prevent leakage of extracellular fluid.

Desmosomes

Anchoring junctions that fasten animal cells together into strong sheets.

Gap junctions

Junctions that provide cytoplasmic channels between adjacent animal cells, allowing materials to pass between them.

Fluid Mosaic Model

A model describing the cell membrane as a mosaic of proteins wedged into a fluid bilayer of phospholipids that can shift and move.

Integral proteins

Membrane proteins that penetrate and reside within the hydrophobic interior of the lipid bilayer.

Peripheral proteins

Membrane proteins that are not embedded in the lipid bilayer but are loosely bound to the surface of the membrane.

Aquaporins

Channel proteins containing hydrophilic channels that specifically facilitate the rapid movement of water molecules across the cell membrane.

Diffusion

The tendency of molecules to spread out evenly into the available space, moving randomly down their concentration gradient from high concentration to low concentration without requiring ATP.

Osmosis

The diffusion of free water across a selectively permeable membrane from a region of lower solute concentration to higher solute concentration.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water.

Isotonic

A solution whose solute concentration is equal to that inside the cell, resulting in no net movement of water across the plasma membrane.

Hypertonic

A solution whose solute concentration is greater than that inside the cell, causing the cell to lose water.

Hypotonic

A solution whose solute concentration is lower than that inside the cell, causing the cell to take up water.

Sodium-potassium pump

An active transport protein in animal cells that uses ATP to pump $3$ sodium ions out of the cell for every $2$ potassium ions imported into the cell against their concentration gradients.

Membrane potential

The voltage difference across a cell's plasma membrane created by the unequal distribution of positive and negative ions.

Electrogenic pump

A transport protein that generates a voltage across a membrane, such as the sodium-potassium pump in animals or the proton pump in plants, fungi, and bacteria.

Cotransport

A mechanism in which a single transport protein couples the downhill diffusion of one solute to the uphill transport of a second substance against its concentration gradient.

Pinocytosis

A type of endocytosis ('cell drinking') where the cell forms vesicles from the plasma membrane to ingest extracellular fluid and its dissolved solutes.

Receptor-mediated endocytosis

A specialized bulk transport mechanism where specific extracellular molecules bind to receptor proteins, triggering vesicle formation to import those substances into the cell.

Familial Hypercholesterolemia

A genetic condition characterized by a lack of functional LDL receptor proteins, hindering cholesterol intake from the bloodstream and contributing to atherosclerosis.