Chapter 3: Cells - The Living Units Flashcards

Vocabulary flashcards covering cellular structures, plasma membrane transport, intercellular junctions, organelles, cytoskeleton, cell division, and protein synthesis.

Cell Theory

The foundational biological principle stating that cells are the structural and functional units of all living things, that an organism's activity depends on cellular function, that structure and function are complementary, and that cells arise from preexisting cells.

Interstitial Fluid

The specific extracellular fluid compartment in which body cells are submersed or bathed.

Fluid Mosaic Model

The structural concept describing the plasma membrane as a double layer of phospholipids with floating proteins that form constantly changing patterns.

Glycocalyx

A cell-surface carbohydrate coating formed by membrane glycolipids and glycoproteins that functions in cell identity, recognition, and immune signaling.

Phospholipids

Membrane lipids that make up $75\times10^{-2}$ (or $75\%$) of total membrane lipids, composed of polar, hydrophilic phosphate heads and nonpolar, hydrophobic fatty acid tails.

Integral Proteins

Membrane proteins firmly embedded in the lipid bilayer (often transmembrane) that function as transport channels, enzymes, or receptors.

Peripheral Proteins

Proteins loosely attached to integral proteins or membrane surfaces that function as enzymes, motor proteins, or structural connections.

Tight Junctions

Impermeable intercellular junctions formed by interlocking junctional proteins that continuous-seal spaces between cells to prevent molecules from passing.

Desmosomes

Anchoring intercellular junctions using cadherin linker proteins and keratin intermediate filaments to bind adjacent cells together like molecular Velcro® and prevent tearing.

Gap Junctions

Communicating intercellular junctions composed of transmembrane proteins called connexons that form channels allowing ions and small molecules to pass directly from cell to cell.

Simple Diffusion

The passive transport process where nonpolar, lipid-soluble solutes move directly through the phospholipid bilayer down their concentration gradient without cellular energy.

Facilitated Diffusion

Passive membrane transport of polar or charged substances mediated by specific transmembrane carrier proteins or channel proteins.

Osmosis

The passive diffusion of solvent water through a selectively permeable membrane, either directly through the lipid bilayer or via aquaporins.

Aquaporins

Transmembrane protein channels specifically dedicated to facilitating the movement of water across the plasma membrane.

Osmolarity

The measure of total solute particle concentration in a solvent, expressed in osmoles per liter ($\text{osmol/L}$).

Hydrostatic Pressure

The outward fluid pressure exerted on the inner cell membrane caused by an increase in intracellular water volume due to osmosis.

Osmotic Pressure

The inward pressure or force reflecting the tendency of water to move into a cell with a higher solute concentration.

Tonicity

The ability of an extracellular solution to alter the shape or tone of cells by changing their internal water volume.

Isotonic Solution

A solution having the same concentration of nonpenetrating solutes as the interior of the cell, allowing cells to maintain their normal shape.

Hypertonic Solution

A solution with a higher concentration of nonpenetrating solutes than inside the cell, causing water to leave the cell and leading to cellular shrinkage (crenation).

Hypotonic Solution

A solution with a lower concentration of nonpenetrating solutes than inside the cell, causing water to enter the cell until it swells and bursts (lyses).

Primary Active Transport

An active transport process that directly consumes energy from ATP hydrolysis to pump solutes against their concentration gradient (e.g., the $\text{Na}^+\text{-K}^+$ pump).

Secondary Active Transport

An active transport mechanism driven indirectly by energy stored in ionic concentration gradients established by primary active transport.

Symporters

Cotransport carrier proteins that move two different solutes across the plasma membrane in the same direction.

Antiporters

Cotransport carrier proteins that transport two different solutes across the plasma membrane in opposite directions.

Phagocytosis

A type of endocytosis where a cell projects pseudopods ('false feet') around large particles or debris to enclose them within a membranous vesicle called a phagosome.

Pinocytosis

A non-specific form of endocytosis (fluid-phase endocytosis) where the cell membrane sinks inward to engulf droplets of extracellular fluid containing dissolved solutes.

Receptor-Mediated Endocytosis

A selective endocytosis process where extracellular substances bind to specific membrane receptors to trigger uptake in protein-coated vesicles.

Exocytosis

An active vesicular transport process where intracellular secretory vesicles fuse with the plasma membrane to release contents to the cell exterior.

v-SNARE

A transmembrane protein located on a secretory vesicle surface that binds to target t-SNARE proteins on the plasma membrane to trigger exocytosis.

t-SNARE

A plasma membrane receptor protein that pairs with v-SNARE proteins on secretory vesicles during exocytosis.

Resting Membrane Potential (RMP)

The voltage or electrical potential energy produced by separation of oppositely charged ions across the plasma membrane in resting cells, typically ranging from $-50\,\text{mV}$ to $-100\,\text{mV}$.

Cell Adhesion Molecules (CAMs)

Membrane glycoproteins that anchor cells to the extracellular matrix or to each other, facilitate cell movement, and signal intracellular cellular activities.

Ligands

Specific chemical messenger molecules (such as hormones and neurotransmitters) that bind selectively to membrane receptors to initiate cellular responses.

Mitochondria

Rodlike, double-membrane organelles with inner membrane folds called cristae that serve as the powerhouse of the cell and primary site of ATP synthesis.

Ribosomes

Dense organelles composed of ribosomal RNA and proteins with two subunits that act as the physical sites of protein synthesis.

Rough Endoplasmic Reticulum

A membranous system studded with ribosomes that attaches sugar groups to proteins, packages proteins into vesicles, and synthesizes membrane phospholipids.

Smooth Endoplasmic Reticulum

A membranous network of sacs and tubules lacking ribosomes that synthesizes lipids and steroids, metabolizes lipids, detoxifies drugs, and stores $\text{Ca}^{2+}$.

Golgi Apparatus

A stack of flattened membranes near the nucleus that modifies, packages, and segregates proteins for secretion, inclusion in lysosomes, or incorporation into the plasma membrane.

Peroxisomes

Membranous sacs containing oxidase and catalase enzymes that detoxify harmful substances and break down hydrogen peroxide.

Lysosomes

Membranous sacs containing acid hydrolases that serve as the main sites of intracellular digestion.

Microtubules

Cylindrical cytoskeletal structures ($25\,\text{nm}$ diameter) made of tubulin proteins that give the cell shape, support intracellular movement, and form centrioles, cilia, and flagella.

Microfilaments

Fine cytoskeletal filaments ($7\,\text{nm}$ diameter) composed of the protein actin involved in muscle contraction and intracellular movement.

Intermediate Filaments

Tough, insoluble protein fibers ($10\,\text{nm}$ diameter) constructed like woven ropes from tetramer fibrils that resist mechanical forces acting on the cell.

Centrioles

Paired cylindrical bodies in the centrosome, composed of nine triplets of microtubules, that organize the mitotic spindle during cell division and form basal bodies.

Microvilli

Tubular extensions of the plasma membrane containing a bundle of actin filaments that function to increase cell surface area for absorption.

Transcription

The synthesis stage in which RNA polymerase unwinds DNA and transfers genetic information from a gene template into a complementary mRNA strand.

Translation

The protein synthesis process where ribosomes decode messenger RNA sequences using tRNA anticodons to assemble amino acids into a polypeptide chain.

messenger RNA (mRNA)

The nucleic acid molecule that carries coded genetic instructions from nuclear DNA into the cytoplasm for protein assembly.

transfer RNA (tRNA)

The RNA molecule that carries specific amino acids to ribosomes and uses its anticodon sequence to decode complementary mRNA codons.